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linux/drivers/gpu/drm/i915/intel_breadcrumbs.c

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drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
/*
* Copyright © 2015 Intel Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*
*/
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
#include <linux/kthread.h>
sched/headers: Prepare for new header dependencies before moving code to <uapi/linux/sched/types.h> We are going to move scheduler ABI details to <uapi/linux/sched/types.h>, which will be used from a number of .c files. Create empty placeholder header that maps to <linux/types.h>. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-02-02 01:07:51 +08:00
#include <uapi/linux/sched/types.h>
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
#include "i915_drv.h"
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
static unsigned int __intel_breadcrumbs_wakeup(struct intel_breadcrumbs *b)
drm/i915: Report both waiters and success from intel_engine_wakeup() The two users of the return value from intel_engine_wakeup() are expecting different results. In the breadcrumbs hangcheck, we are using it to determine whether wake_up_process() detected the waiter was currently running (and if so we presume that it hasn't yet missed the interrupt). However, in the fake_irq path, we are using the return value as a check as to whether there are any waiters, and so we may incorrectly stop the fake-irq if that waiter was currently running. To handle the two different needs, return both bits of information! We uninline it from the irq path in preparation for the next patch which makes the irq hotpath special and relegates intel_engine_wakeup() to the slow fixup paths. v2: s/ret/result/ Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-1-chris@chris-wilson.co.uk
2017-02-28 04:58:47 +08:00
{
drm/i915: Signal first fence from irq handler if complete As execlists and other non-semaphore multi-engine devices coordinate between engines using interrupts, we can shave off a few 10s of microsecond of scheduling latency by doing the fence signaling from the interrupt as opposed to a RT kthread. (Realistically the delay adds about 1% to an individual cross-engine workload.) We only signal the first fence in order to limit the amount of work we move into the interrupt handler. We also have to remember that our breadcrumbs may be unordered with respect to the interrupt and so we still require the waiter process to perform some heavyweight coherency fixups, as well as traversing the tree of waiters. v2: No need for early exit in irq handler - it breaks the flow between patches and prevents the tracepoint v3: Restore rcu hold across irq signaling of request Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-2-chris@chris-wilson.co.uk
2017-02-28 04:58:48 +08:00
struct intel_wait *wait;
drm/i915: Report both waiters and success from intel_engine_wakeup() The two users of the return value from intel_engine_wakeup() are expecting different results. In the breadcrumbs hangcheck, we are using it to determine whether wake_up_process() detected the waiter was currently running (and if so we presume that it hasn't yet missed the interrupt). However, in the fake_irq path, we are using the return value as a check as to whether there are any waiters, and so we may incorrectly stop the fake-irq if that waiter was currently running. To handle the two different needs, return both bits of information! We uninline it from the irq path in preparation for the next patch which makes the irq hotpath special and relegates intel_engine_wakeup() to the slow fixup paths. v2: s/ret/result/ Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-1-chris@chris-wilson.co.uk
2017-02-28 04:58:47 +08:00
unsigned int result = 0;
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
lockdep_assert_held(&b->irq_lock);
wait = b->irq_wait;
drm/i915: Signal first fence from irq handler if complete As execlists and other non-semaphore multi-engine devices coordinate between engines using interrupts, we can shave off a few 10s of microsecond of scheduling latency by doing the fence signaling from the interrupt as opposed to a RT kthread. (Realistically the delay adds about 1% to an individual cross-engine workload.) We only signal the first fence in order to limit the amount of work we move into the interrupt handler. We also have to remember that our breadcrumbs may be unordered with respect to the interrupt and so we still require the waiter process to perform some heavyweight coherency fixups, as well as traversing the tree of waiters. v2: No need for early exit in irq handler - it breaks the flow between patches and prevents the tracepoint v3: Restore rcu hold across irq signaling of request Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-2-chris@chris-wilson.co.uk
2017-02-28 04:58:48 +08:00
if (wait) {
drm/i915: Report both waiters and success from intel_engine_wakeup() The two users of the return value from intel_engine_wakeup() are expecting different results. In the breadcrumbs hangcheck, we are using it to determine whether wake_up_process() detected the waiter was currently running (and if so we presume that it hasn't yet missed the interrupt). However, in the fake_irq path, we are using the return value as a check as to whether there are any waiters, and so we may incorrectly stop the fake-irq if that waiter was currently running. To handle the two different needs, return both bits of information! We uninline it from the irq path in preparation for the next patch which makes the irq hotpath special and relegates intel_engine_wakeup() to the slow fixup paths. v2: s/ret/result/ Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-1-chris@chris-wilson.co.uk
2017-02-28 04:58:47 +08:00
result = ENGINE_WAKEUP_WAITER;
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
if (wake_up_process(wait->tsk))
result |= ENGINE_WAKEUP_ASLEEP;
drm/i915: Report both waiters and success from intel_engine_wakeup() The two users of the return value from intel_engine_wakeup() are expecting different results. In the breadcrumbs hangcheck, we are using it to determine whether wake_up_process() detected the waiter was currently running (and if so we presume that it hasn't yet missed the interrupt). However, in the fake_irq path, we are using the return value as a check as to whether there are any waiters, and so we may incorrectly stop the fake-irq if that waiter was currently running. To handle the two different needs, return both bits of information! We uninline it from the irq path in preparation for the next patch which makes the irq hotpath special and relegates intel_engine_wakeup() to the slow fixup paths. v2: s/ret/result/ Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-1-chris@chris-wilson.co.uk
2017-02-28 04:58:47 +08:00
}
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
return result;
}
unsigned int intel_engine_wakeup(struct intel_engine_cs *engine)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Protect intel_engine_wakeup() for call from irq context intel_engine_wakeup() is called by nop_request_submit() which is installed to handle third party fences completed from within irq context. As such, it needs the full irqsave/irqrestore and not the partial spin_irq_lock handling. [18942.714467] ================================= [18942.719076] [ INFO: inconsistent lock state ] [18942.723522] 4.11.0-rc2-CI-CI_DRM_2368+ #1 Tainted: G U W [18942.729970] --------------------------------- [18942.734466] inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage. [18942.740594] gem_eio/1275 [HC0[0]:SC0[0]:HE1:SE1] takes: [18942.745932] (&(&fence->lock)->rlock){+.?...}, at: [<ffffffff815ec100>] dma_fence_signal+0x100/0x 230 [18942.755331] {IN-SOFTIRQ-W} state was registered at: [18942.760356] __lock_acquire+0x5d0/0x1bb0 [18942.764444] lock_acquire+0xc9/0x220 [18942.768196] _raw_spin_lock_irqsave+0x41/0x60 [18942.772747] dma_fence_signal+0x100/0x230 [18942.776927] vgem_fence_timeout+0x9/0x10 [vgem] [18942.781701] call_timer_fn+0x92/0x380 [18942.785557] expire_timers+0x150/0x1f0 [18942.789491] run_timer_softirq+0x7c/0x160 [18942.793705] __do_softirq+0x116/0x4c0 [18942.797560] irq_exit+0xa9/0xc0 [18942.800873] smp_apic_timer_interrupt+0x38/0x50 [18942.805611] apic_timer_interrupt+0x90/0xa0 [18942.810008] cpuidle_enter_state+0x135/0x380 [18942.814503] cpuidle_enter+0x12/0x20 [18942.818250] call_cpuidle+0x1e/0x40 [18942.821906] do_idle+0x17e/0x1f0 [18942.825333] cpu_startup_entry+0x18/0x20 [18942.829463] rest_init+0x127/0x130 [18942.833025] start_kernel+0x3f1/0x3fe [18942.836908] x86_64_start_reservations+0x2a/0x2c [18942.841733] x86_64_start_kernel+0x173/0x186 [18942.846234] verify_cpu+0x0/0xfc [18942.849604] irq event stamp: 30568 [18942.853140] hardirqs last enabled at (30567): [<ffffffff8110b81f>] ktime_get+0xef/0x120 [18942.861468] hardirqs last disabled at (30568): [<ffffffff81876377>] _raw_spin_lock_irqsave+0x17/0 x60 [18942.870812] softirqs last enabled at (30462): [<ffffffff81085cd9>] __do_softirq+0x1d9/0x4c0 [18942.879443] softirqs last disabled at (30439): [<ffffffff81086139>] irq_exit+0xa9/0xc0 [18942.887616] [18942.887616] other info that might help us debug this: [18942.894279] Possible unsafe locking scenario: [18942.894279] [18942.900336] CPU0 [18942.902851] ---- [18942.905362] lock(&(&fence->lock)->rlock); [18942.909647] <Interrupt> [18942.912330] lock(&(&fence->lock)->rlock); [18942.916821] [18942.916821] *** DEADLOCK *** [18942.916821] [18942.922862] 1 lock held by gem_eio/1275: [18942.926859] #0: (&(&fence->lock)->rlock){+.?...}, at: [<ffffffff815ec100>] dma_fence_signal+0x1 00/0x230 [18942.936651] [18942.936651] stack backtrace: [18942.941142] CPU: 3 PID: 1275 Comm: gem_eio Tainted: G U W 4.11.0-rc2-CI-CI_DRM_2368+ # 1 [18942.950367] Hardware name: Gigabyte Technology Co., Ltd. Z170X-UD5/Z170X-UD5-CF, BIOS F21 01/06/2 017 [18942.959756] Call Trace: [18942.962244] dump_stack+0x67/0x92 [18942.965626] print_usage_bug.part.23+0x259/0x268 [18942.970362] mark_lock+0x12c/0x6f0 [18942.973851] ? check_usage_forwards+0x130/0x130 [18942.978487] mark_held_locks+0x6f/0xa0 [18942.982329] ? _raw_spin_unlock_irq+0x27/0x50 [18942.986797] trace_hardirqs_on_caller+0x150/0x200 [18942.991599] trace_hardirqs_on+0xd/0x10 [18942.995515] _raw_spin_unlock_irq+0x27/0x50 [18942.999796] intel_engine_wakeup+0x26/0x30 [i915] [18943.004670] intel_engine_init_global_seqno+0x131/0x1a0 [i915] [18943.010745] nop_submit_request+0x2e/0x40 [i915] [18943.015476] submit_notify+0x3f/0x5c [i915] [18943.019763] __i915_sw_fence_complete+0x176/0x220 [i915] [18943.025234] ? try_to_del_timer_sync+0x4d/0x60 [18943.029825] i915_sw_fence_complete+0x25/0x40 [i915] [18943.034887] dma_i915_sw_fence_wake+0x26/0x60 [i915] [18943.039959] dma_fence_signal+0x146/0x230 [18943.044109] vgem_fence_signal_ioctl+0x6c/0xc0 [vgem] [18943.049275] drm_ioctl+0x200/0x450 [18943.052758] ? vgem_fence_attach_ioctl+0x270/0x270 [vgem] [18943.058334] do_vfs_ioctl+0x90/0x6e0 [18943.061991] ? entry_SYSCALL_64_fastpath+0x5/0xb1 [18943.066843] ? __this_cpu_preempt_check+0x13/0x20 [18943.071643] ? trace_hardirqs_on_caller+0xe7/0x200 [18943.076532] SyS_ioctl+0x3c/0x70 [18943.079842] entry_SYSCALL_64_fastpath+0x1c/0xb1 [18943.084558] RIP: 0033:0x7f0dfcc14357 [18943.088240] RSP: 002b:00007ffeb4628da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [18943.095996] RAX: ffffffffffffffda RBX: ffffffff8147eb93 RCX: 00007f0dfcc14357 [18943.103311] RDX: 00007ffeb4628de0 RSI: 0000000040086442 RDI: 0000000000000005 [18943.110574] RBP: ffffc9000176ff88 R08: 0000000000000004 R09: 0000000000000000 [18943.117845] R10: 0000000000000029 R11: 0000000000000246 R12: 0000000000000001 [18943.125168] R13: 0000000000000005 R14: 0000000040086442 R15: 0000000000000000 [18943.132520] ? __this_cpu_preempt_check+0x13/0x20 Fixes: cdc3a4539034 ("drm/i915: No need to save/restore irq status in intel_engine_wakeup") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170320143133.1507-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-03-20 22:31:33 +08:00
unsigned long flags;
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
unsigned int result;
drm/i915: Protect intel_engine_wakeup() for call from irq context intel_engine_wakeup() is called by nop_request_submit() which is installed to handle third party fences completed from within irq context. As such, it needs the full irqsave/irqrestore and not the partial spin_irq_lock handling. [18942.714467] ================================= [18942.719076] [ INFO: inconsistent lock state ] [18942.723522] 4.11.0-rc2-CI-CI_DRM_2368+ #1 Tainted: G U W [18942.729970] --------------------------------- [18942.734466] inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage. [18942.740594] gem_eio/1275 [HC0[0]:SC0[0]:HE1:SE1] takes: [18942.745932] (&(&fence->lock)->rlock){+.?...}, at: [<ffffffff815ec100>] dma_fence_signal+0x100/0x 230 [18942.755331] {IN-SOFTIRQ-W} state was registered at: [18942.760356] __lock_acquire+0x5d0/0x1bb0 [18942.764444] lock_acquire+0xc9/0x220 [18942.768196] _raw_spin_lock_irqsave+0x41/0x60 [18942.772747] dma_fence_signal+0x100/0x230 [18942.776927] vgem_fence_timeout+0x9/0x10 [vgem] [18942.781701] call_timer_fn+0x92/0x380 [18942.785557] expire_timers+0x150/0x1f0 [18942.789491] run_timer_softirq+0x7c/0x160 [18942.793705] __do_softirq+0x116/0x4c0 [18942.797560] irq_exit+0xa9/0xc0 [18942.800873] smp_apic_timer_interrupt+0x38/0x50 [18942.805611] apic_timer_interrupt+0x90/0xa0 [18942.810008] cpuidle_enter_state+0x135/0x380 [18942.814503] cpuidle_enter+0x12/0x20 [18942.818250] call_cpuidle+0x1e/0x40 [18942.821906] do_idle+0x17e/0x1f0 [18942.825333] cpu_startup_entry+0x18/0x20 [18942.829463] rest_init+0x127/0x130 [18942.833025] start_kernel+0x3f1/0x3fe [18942.836908] x86_64_start_reservations+0x2a/0x2c [18942.841733] x86_64_start_kernel+0x173/0x186 [18942.846234] verify_cpu+0x0/0xfc [18942.849604] irq event stamp: 30568 [18942.853140] hardirqs last enabled at (30567): [<ffffffff8110b81f>] ktime_get+0xef/0x120 [18942.861468] hardirqs last disabled at (30568): [<ffffffff81876377>] _raw_spin_lock_irqsave+0x17/0 x60 [18942.870812] softirqs last enabled at (30462): [<ffffffff81085cd9>] __do_softirq+0x1d9/0x4c0 [18942.879443] softirqs last disabled at (30439): [<ffffffff81086139>] irq_exit+0xa9/0xc0 [18942.887616] [18942.887616] other info that might help us debug this: [18942.894279] Possible unsafe locking scenario: [18942.894279] [18942.900336] CPU0 [18942.902851] ---- [18942.905362] lock(&(&fence->lock)->rlock); [18942.909647] <Interrupt> [18942.912330] lock(&(&fence->lock)->rlock); [18942.916821] [18942.916821] *** DEADLOCK *** [18942.916821] [18942.922862] 1 lock held by gem_eio/1275: [18942.926859] #0: (&(&fence->lock)->rlock){+.?...}, at: [<ffffffff815ec100>] dma_fence_signal+0x1 00/0x230 [18942.936651] [18942.936651] stack backtrace: [18942.941142] CPU: 3 PID: 1275 Comm: gem_eio Tainted: G U W 4.11.0-rc2-CI-CI_DRM_2368+ # 1 [18942.950367] Hardware name: Gigabyte Technology Co., Ltd. Z170X-UD5/Z170X-UD5-CF, BIOS F21 01/06/2 017 [18942.959756] Call Trace: [18942.962244] dump_stack+0x67/0x92 [18942.965626] print_usage_bug.part.23+0x259/0x268 [18942.970362] mark_lock+0x12c/0x6f0 [18942.973851] ? check_usage_forwards+0x130/0x130 [18942.978487] mark_held_locks+0x6f/0xa0 [18942.982329] ? _raw_spin_unlock_irq+0x27/0x50 [18942.986797] trace_hardirqs_on_caller+0x150/0x200 [18942.991599] trace_hardirqs_on+0xd/0x10 [18942.995515] _raw_spin_unlock_irq+0x27/0x50 [18942.999796] intel_engine_wakeup+0x26/0x30 [i915] [18943.004670] intel_engine_init_global_seqno+0x131/0x1a0 [i915] [18943.010745] nop_submit_request+0x2e/0x40 [i915] [18943.015476] submit_notify+0x3f/0x5c [i915] [18943.019763] __i915_sw_fence_complete+0x176/0x220 [i915] [18943.025234] ? try_to_del_timer_sync+0x4d/0x60 [18943.029825] i915_sw_fence_complete+0x25/0x40 [i915] [18943.034887] dma_i915_sw_fence_wake+0x26/0x60 [i915] [18943.039959] dma_fence_signal+0x146/0x230 [18943.044109] vgem_fence_signal_ioctl+0x6c/0xc0 [vgem] [18943.049275] drm_ioctl+0x200/0x450 [18943.052758] ? vgem_fence_attach_ioctl+0x270/0x270 [vgem] [18943.058334] do_vfs_ioctl+0x90/0x6e0 [18943.061991] ? entry_SYSCALL_64_fastpath+0x5/0xb1 [18943.066843] ? __this_cpu_preempt_check+0x13/0x20 [18943.071643] ? trace_hardirqs_on_caller+0xe7/0x200 [18943.076532] SyS_ioctl+0x3c/0x70 [18943.079842] entry_SYSCALL_64_fastpath+0x1c/0xb1 [18943.084558] RIP: 0033:0x7f0dfcc14357 [18943.088240] RSP: 002b:00007ffeb4628da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [18943.095996] RAX: ffffffffffffffda RBX: ffffffff8147eb93 RCX: 00007f0dfcc14357 [18943.103311] RDX: 00007ffeb4628de0 RSI: 0000000040086442 RDI: 0000000000000005 [18943.110574] RBP: ffffc9000176ff88 R08: 0000000000000004 R09: 0000000000000000 [18943.117845] R10: 0000000000000029 R11: 0000000000000246 R12: 0000000000000001 [18943.125168] R13: 0000000000000005 R14: 0000000040086442 R15: 0000000000000000 [18943.132520] ? __this_cpu_preempt_check+0x13/0x20 Fixes: cdc3a4539034 ("drm/i915: No need to save/restore irq status in intel_engine_wakeup") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170320143133.1507-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-03-20 22:31:33 +08:00
spin_lock_irqsave(&b->irq_lock, flags);
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
result = __intel_breadcrumbs_wakeup(b);
drm/i915: Protect intel_engine_wakeup() for call from irq context intel_engine_wakeup() is called by nop_request_submit() which is installed to handle third party fences completed from within irq context. As such, it needs the full irqsave/irqrestore and not the partial spin_irq_lock handling. [18942.714467] ================================= [18942.719076] [ INFO: inconsistent lock state ] [18942.723522] 4.11.0-rc2-CI-CI_DRM_2368+ #1 Tainted: G U W [18942.729970] --------------------------------- [18942.734466] inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage. [18942.740594] gem_eio/1275 [HC0[0]:SC0[0]:HE1:SE1] takes: [18942.745932] (&(&fence->lock)->rlock){+.?...}, at: [<ffffffff815ec100>] dma_fence_signal+0x100/0x 230 [18942.755331] {IN-SOFTIRQ-W} state was registered at: [18942.760356] __lock_acquire+0x5d0/0x1bb0 [18942.764444] lock_acquire+0xc9/0x220 [18942.768196] _raw_spin_lock_irqsave+0x41/0x60 [18942.772747] dma_fence_signal+0x100/0x230 [18942.776927] vgem_fence_timeout+0x9/0x10 [vgem] [18942.781701] call_timer_fn+0x92/0x380 [18942.785557] expire_timers+0x150/0x1f0 [18942.789491] run_timer_softirq+0x7c/0x160 [18942.793705] __do_softirq+0x116/0x4c0 [18942.797560] irq_exit+0xa9/0xc0 [18942.800873] smp_apic_timer_interrupt+0x38/0x50 [18942.805611] apic_timer_interrupt+0x90/0xa0 [18942.810008] cpuidle_enter_state+0x135/0x380 [18942.814503] cpuidle_enter+0x12/0x20 [18942.818250] call_cpuidle+0x1e/0x40 [18942.821906] do_idle+0x17e/0x1f0 [18942.825333] cpu_startup_entry+0x18/0x20 [18942.829463] rest_init+0x127/0x130 [18942.833025] start_kernel+0x3f1/0x3fe [18942.836908] x86_64_start_reservations+0x2a/0x2c [18942.841733] x86_64_start_kernel+0x173/0x186 [18942.846234] verify_cpu+0x0/0xfc [18942.849604] irq event stamp: 30568 [18942.853140] hardirqs last enabled at (30567): [<ffffffff8110b81f>] ktime_get+0xef/0x120 [18942.861468] hardirqs last disabled at (30568): [<ffffffff81876377>] _raw_spin_lock_irqsave+0x17/0 x60 [18942.870812] softirqs last enabled at (30462): [<ffffffff81085cd9>] __do_softirq+0x1d9/0x4c0 [18942.879443] softirqs last disabled at (30439): [<ffffffff81086139>] irq_exit+0xa9/0xc0 [18942.887616] [18942.887616] other info that might help us debug this: [18942.894279] Possible unsafe locking scenario: [18942.894279] [18942.900336] CPU0 [18942.902851] ---- [18942.905362] lock(&(&fence->lock)->rlock); [18942.909647] <Interrupt> [18942.912330] lock(&(&fence->lock)->rlock); [18942.916821] [18942.916821] *** DEADLOCK *** [18942.916821] [18942.922862] 1 lock held by gem_eio/1275: [18942.926859] #0: (&(&fence->lock)->rlock){+.?...}, at: [<ffffffff815ec100>] dma_fence_signal+0x1 00/0x230 [18942.936651] [18942.936651] stack backtrace: [18942.941142] CPU: 3 PID: 1275 Comm: gem_eio Tainted: G U W 4.11.0-rc2-CI-CI_DRM_2368+ # 1 [18942.950367] Hardware name: Gigabyte Technology Co., Ltd. Z170X-UD5/Z170X-UD5-CF, BIOS F21 01/06/2 017 [18942.959756] Call Trace: [18942.962244] dump_stack+0x67/0x92 [18942.965626] print_usage_bug.part.23+0x259/0x268 [18942.970362] mark_lock+0x12c/0x6f0 [18942.973851] ? check_usage_forwards+0x130/0x130 [18942.978487] mark_held_locks+0x6f/0xa0 [18942.982329] ? _raw_spin_unlock_irq+0x27/0x50 [18942.986797] trace_hardirqs_on_caller+0x150/0x200 [18942.991599] trace_hardirqs_on+0xd/0x10 [18942.995515] _raw_spin_unlock_irq+0x27/0x50 [18942.999796] intel_engine_wakeup+0x26/0x30 [i915] [18943.004670] intel_engine_init_global_seqno+0x131/0x1a0 [i915] [18943.010745] nop_submit_request+0x2e/0x40 [i915] [18943.015476] submit_notify+0x3f/0x5c [i915] [18943.019763] __i915_sw_fence_complete+0x176/0x220 [i915] [18943.025234] ? try_to_del_timer_sync+0x4d/0x60 [18943.029825] i915_sw_fence_complete+0x25/0x40 [i915] [18943.034887] dma_i915_sw_fence_wake+0x26/0x60 [i915] [18943.039959] dma_fence_signal+0x146/0x230 [18943.044109] vgem_fence_signal_ioctl+0x6c/0xc0 [vgem] [18943.049275] drm_ioctl+0x200/0x450 [18943.052758] ? vgem_fence_attach_ioctl+0x270/0x270 [vgem] [18943.058334] do_vfs_ioctl+0x90/0x6e0 [18943.061991] ? entry_SYSCALL_64_fastpath+0x5/0xb1 [18943.066843] ? __this_cpu_preempt_check+0x13/0x20 [18943.071643] ? trace_hardirqs_on_caller+0xe7/0x200 [18943.076532] SyS_ioctl+0x3c/0x70 [18943.079842] entry_SYSCALL_64_fastpath+0x1c/0xb1 [18943.084558] RIP: 0033:0x7f0dfcc14357 [18943.088240] RSP: 002b:00007ffeb4628da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [18943.095996] RAX: ffffffffffffffda RBX: ffffffff8147eb93 RCX: 00007f0dfcc14357 [18943.103311] RDX: 00007ffeb4628de0 RSI: 0000000040086442 RDI: 0000000000000005 [18943.110574] RBP: ffffc9000176ff88 R08: 0000000000000004 R09: 0000000000000000 [18943.117845] R10: 0000000000000029 R11: 0000000000000246 R12: 0000000000000001 [18943.125168] R13: 0000000000000005 R14: 0000000040086442 R15: 0000000000000000 [18943.132520] ? __this_cpu_preempt_check+0x13/0x20 Fixes: cdc3a4539034 ("drm/i915: No need to save/restore irq status in intel_engine_wakeup") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170320143133.1507-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-03-20 22:31:33 +08:00
spin_unlock_irqrestore(&b->irq_lock, flags);
drm/i915: Report both waiters and success from intel_engine_wakeup() The two users of the return value from intel_engine_wakeup() are expecting different results. In the breadcrumbs hangcheck, we are using it to determine whether wake_up_process() detected the waiter was currently running (and if so we presume that it hasn't yet missed the interrupt). However, in the fake_irq path, we are using the return value as a check as to whether there are any waiters, and so we may incorrectly stop the fake-irq if that waiter was currently running. To handle the two different needs, return both bits of information! We uninline it from the irq path in preparation for the next patch which makes the irq hotpath special and relegates intel_engine_wakeup() to the slow fixup paths. v2: s/ret/result/ Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-1-chris@chris-wilson.co.uk
2017-02-28 04:58:47 +08:00
return result;
}
drm/i915: Postpone fake breadcrumb interrupt until real interrupts cease When the timer expires for checking on interrupt processing, check to see if any interrupts arrived within the last time period. If real interrupts are still being delivered, we can be reassured that we haven't missed the final interrupt as the waiter will still be woken. Only once all activity ceases, do we have to worry about the waiter never being woken and so need to install a timer to kick the waiter for a slow arrival of a seqno. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170217151304.16665-2-chris@chris-wilson.co.uk
2017-02-17 23:13:00 +08:00
static unsigned long wait_timeout(void)
{
return round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES);
}
drm/i915: Consolidate reporting of "missed breadcrumbs" Move the setting of gpu_error->missed_irq_ring bit to a common function so that we can get the debug logging for either path. v2: Add %pF caller Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170228085018.3225-1-chris@chris-wilson.co.uk
2017-02-28 16:50:18 +08:00
static noinline void missed_breadcrumb(struct intel_engine_cs *engine)
{
drm/i915: Include interesting seqno in the missed breadcrumb debug Knowing the neighbouring seqno (current on hw, last submitted to hw) provide some useful breadcrumbs to the debug log. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/20170423170619.7156-4-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
2017-04-24 01:06:19 +08:00
DRM_DEBUG_DRIVER("%s missed breadcrumb at %pF, irq posted? %s, current seqno=%x, last=%x\n",
drm/i915: Consolidate reporting of "missed breadcrumbs" Move the setting of gpu_error->missed_irq_ring bit to a common function so that we can get the debug logging for either path. v2: Add %pF caller Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170228085018.3225-1-chris@chris-wilson.co.uk
2017-02-28 16:50:18 +08:00
engine->name, __builtin_return_address(0),
yesno(test_bit(ENGINE_IRQ_BREADCRUMB,
drm/i915: Include interesting seqno in the missed breadcrumb debug Knowing the neighbouring seqno (current on hw, last submitted to hw) provide some useful breadcrumbs to the debug log. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/20170423170619.7156-4-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
2017-04-24 01:06:19 +08:00
&engine->irq_posted)),
intel_engine_get_seqno(engine),
intel_engine_last_submit(engine));
drm/i915: Consolidate reporting of "missed breadcrumbs" Move the setting of gpu_error->missed_irq_ring bit to a common function so that we can get the debug logging for either path. v2: Add %pF caller Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170228085018.3225-1-chris@chris-wilson.co.uk
2017-02-28 16:50:18 +08:00
set_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
}
drm/i915: Move missed interrupt detection from hangcheck to breadcrumbs In commit 2529d57050af ("drm/i915: Drop racy markup of missed-irqs from idle-worker") the racy detection of missed interrupts was removed when we went idle. This however opened up the issue that the stuck waiters were not being reported, causing a test case failure. If we move the stuck waiter detection out of hangcheck and into the breadcrumb mechanims (i.e. the waiter) itself, we can avoid this issue entirely. This leaves hangcheck looking for a stuck GPU (inspecting for request advancement and HEAD motion), and breadcrumbs looking for a stuck waiter - hopefully make both easier to understand by their segregation. v2: Reduce the error message as we now run independently of hangcheck, and the hanging batch used by igt also counts as a stuck waiter causing extra warnings in dmesg. v3: Move the breadcrumb's hangcheck kickstart to the first missed wait. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97104 Fixes: 2529d57050af (waiter"drm/i915: Drop racy markup of missed-irqs...") Testcase: igt/drv_missed_irq Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1470761272-1245-2-git-send-email-chris@chris-wilson.co.uk
2016-08-10 00:47:51 +08:00
static void intel_breadcrumbs_hangcheck(unsigned long data)
{
struct intel_engine_cs *engine = (struct intel_engine_cs *)data;
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
if (!b->irq_armed)
drm/i915: Move missed interrupt detection from hangcheck to breadcrumbs In commit 2529d57050af ("drm/i915: Drop racy markup of missed-irqs from idle-worker") the racy detection of missed interrupts was removed when we went idle. This however opened up the issue that the stuck waiters were not being reported, causing a test case failure. If we move the stuck waiter detection out of hangcheck and into the breadcrumb mechanims (i.e. the waiter) itself, we can avoid this issue entirely. This leaves hangcheck looking for a stuck GPU (inspecting for request advancement and HEAD motion), and breadcrumbs looking for a stuck waiter - hopefully make both easier to understand by their segregation. v2: Reduce the error message as we now run independently of hangcheck, and the hanging batch used by igt also counts as a stuck waiter causing extra warnings in dmesg. v3: Move the breadcrumb's hangcheck kickstart to the first missed wait. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97104 Fixes: 2529d57050af (waiter"drm/i915: Drop racy markup of missed-irqs...") Testcase: igt/drv_missed_irq Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1470761272-1245-2-git-send-email-chris@chris-wilson.co.uk
2016-08-10 00:47:51 +08:00
return;
drm/i915: Postpone fake breadcrumb interrupt until real interrupts cease When the timer expires for checking on interrupt processing, check to see if any interrupts arrived within the last time period. If real interrupts are still being delivered, we can be reassured that we haven't missed the final interrupt as the waiter will still be woken. Only once all activity ceases, do we have to worry about the waiter never being woken and so need to install a timer to kick the waiter for a slow arrival of a seqno. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170217151304.16665-2-chris@chris-wilson.co.uk
2017-02-17 23:13:00 +08:00
if (b->hangcheck_interrupts != atomic_read(&engine->irq_count)) {
b->hangcheck_interrupts = atomic_read(&engine->irq_count);
mod_timer(&b->hangcheck, wait_timeout());
drm/i915: Move missed interrupt detection from hangcheck to breadcrumbs In commit 2529d57050af ("drm/i915: Drop racy markup of missed-irqs from idle-worker") the racy detection of missed interrupts was removed when we went idle. This however opened up the issue that the stuck waiters were not being reported, causing a test case failure. If we move the stuck waiter detection out of hangcheck and into the breadcrumb mechanims (i.e. the waiter) itself, we can avoid this issue entirely. This leaves hangcheck looking for a stuck GPU (inspecting for request advancement and HEAD motion), and breadcrumbs looking for a stuck waiter - hopefully make both easier to understand by their segregation. v2: Reduce the error message as we now run independently of hangcheck, and the hanging batch used by igt also counts as a stuck waiter causing extra warnings in dmesg. v3: Move the breadcrumb's hangcheck kickstart to the first missed wait. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97104 Fixes: 2529d57050af (waiter"drm/i915: Drop racy markup of missed-irqs...") Testcase: igt/drv_missed_irq Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1470761272-1245-2-git-send-email-chris@chris-wilson.co.uk
2016-08-10 00:47:51 +08:00
return;
}
drm/i915/breadcrumbs: Tweak commentary Tvrtko spotted a stale reference to b->lock (now b->rb_lock) so review the comments and try to improve them in passing. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315222259.1469-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-03-16 06:22:59 +08:00
/* We keep the hangcheck timer alive until we disarm the irq, even
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
* if there are no waiters at present.
*
* If the waiter was currently running, assume it hasn't had a chance
drm/i915: Defer declaration of missed-interrupt until the waiter is asleep If the waiter was currently running, assume it hasn't had a chance to process the pending interrupt (e.g, low priority task on a loaded system) and wait until it sleeps before declaring a missed interrupt. References: https://bugs.freedesktop.org/show_bug.cgi?id=99816 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170217151304.16665-4-chris@chris-wilson.co.uk
2017-02-17 23:13:02 +08:00
* to process the pending interrupt (e.g, low priority task on a loaded
* system) and wait until it sleeps before declaring a missed interrupt.
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
*
* If the waiter was asleep (and not even pending a wakeup), then we
* must have missed an interrupt as the GPU has stopped advancing
* but we still have a waiter. Assuming all batches complete within
* DRM_I915_HANGCHECK_JIFFIES [1.5s]!
drm/i915: Defer declaration of missed-interrupt until the waiter is asleep If the waiter was currently running, assume it hasn't had a chance to process the pending interrupt (e.g, low priority task on a loaded system) and wait until it sleeps before declaring a missed interrupt. References: https://bugs.freedesktop.org/show_bug.cgi?id=99816 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170217151304.16665-4-chris@chris-wilson.co.uk
2017-02-17 23:13:02 +08:00
*/
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
if (intel_engine_wakeup(engine) & ENGINE_WAKEUP_ASLEEP) {
drm/i915: Consolidate reporting of "missed breadcrumbs" Move the setting of gpu_error->missed_irq_ring bit to a common function so that we can get the debug logging for either path. v2: Add %pF caller Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170228085018.3225-1-chris@chris-wilson.co.uk
2017-02-28 16:50:18 +08:00
missed_breadcrumb(engine);
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
} else {
drm/i915: Defer declaration of missed-interrupt until the waiter is asleep If the waiter was currently running, assume it hasn't had a chance to process the pending interrupt (e.g, low priority task on a loaded system) and wait until it sleeps before declaring a missed interrupt. References: https://bugs.freedesktop.org/show_bug.cgi?id=99816 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170217151304.16665-4-chris@chris-wilson.co.uk
2017-02-17 23:13:02 +08:00
mod_timer(&b->hangcheck, wait_timeout());
}
drm/i915: Move missed interrupt detection from hangcheck to breadcrumbs In commit 2529d57050af ("drm/i915: Drop racy markup of missed-irqs from idle-worker") the racy detection of missed interrupts was removed when we went idle. This however opened up the issue that the stuck waiters were not being reported, causing a test case failure. If we move the stuck waiter detection out of hangcheck and into the breadcrumb mechanims (i.e. the waiter) itself, we can avoid this issue entirely. This leaves hangcheck looking for a stuck GPU (inspecting for request advancement and HEAD motion), and breadcrumbs looking for a stuck waiter - hopefully make both easier to understand by their segregation. v2: Reduce the error message as we now run independently of hangcheck, and the hanging batch used by igt also counts as a stuck waiter causing extra warnings in dmesg. v3: Move the breadcrumb's hangcheck kickstart to the first missed wait. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97104 Fixes: 2529d57050af (waiter"drm/i915: Drop racy markup of missed-irqs...") Testcase: igt/drv_missed_irq Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1470761272-1245-2-git-send-email-chris@chris-wilson.co.uk
2016-08-10 00:47:51 +08:00
}
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
static void intel_breadcrumbs_fake_irq(unsigned long data)
{
struct intel_engine_cs *engine = (struct intel_engine_cs *)data;
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
drm/i915/breadcrumbs: Tweak commentary Tvrtko spotted a stale reference to b->lock (now b->rb_lock) so review the comments and try to improve them in passing. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315222259.1469-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-03-16 06:22:59 +08:00
/* The timer persists in case we cannot enable interrupts,
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
* or if we have previously seen seqno/interrupt incoherency
drm/i915/breadcrumbs: Tweak commentary Tvrtko spotted a stale reference to b->lock (now b->rb_lock) so review the comments and try to improve them in passing. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315222259.1469-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-03-16 06:22:59 +08:00
* ("missed interrupt" syndrome, better known as a "missed breadcrumb").
* Here the worker will wake up every jiffie in order to kick the
* oldest waiter to do the coherent seqno check.
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
*/
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
drm/i915: No need to save/restore irq status in intel_breadcrumbs_fake_irq Timer callback is a known context so it is correct to always disable interrupts. Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
2017-03-06 23:03:20 +08:00
spin_lock_irq(&b->irq_lock);
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
if (!__intel_breadcrumbs_wakeup(b))
__intel_engine_disarm_breadcrumbs(engine);
drm/i915: No need to save/restore irq status in intel_breadcrumbs_fake_irq Timer callback is a known context so it is correct to always disable interrupts. Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
2017-03-06 23:03:20 +08:00
spin_unlock_irq(&b->irq_lock);
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
if (!b->irq_armed)
drm/i915: Defer enabling hangcheck to the first fake breadcrumb interrupt By deferring hangcheck to the fake breadcrumb interrupt, we can simply the enabling procedure slightly - as by enabling the fake, we then enable the hangcheck. By always enabling the hangcheck from each fake interrupt (it will be a no-op for an already queued hangcheck), it will make restoring the breadcrumbs after a reset simpler in the next patch. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-3-chris@chris-wilson.co.uk
2017-02-28 04:58:49 +08:00
return;
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
mod_timer(&b->fake_irq, jiffies + 1);
drm/i915: Defer enabling hangcheck to the first fake breadcrumb interrupt By deferring hangcheck to the fake breadcrumb interrupt, we can simply the enabling procedure slightly - as by enabling the fake, we then enable the hangcheck. By always enabling the hangcheck from each fake interrupt (it will be a no-op for an already queued hangcheck), it will make restoring the breadcrumbs after a reset simpler in the next patch. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-3-chris@chris-wilson.co.uk
2017-02-28 04:58:49 +08:00
/* Ensure that even if the GPU hangs, we get woken up.
*
* However, note that if no one is waiting, we never notice
* a gpu hang. Eventually, we will have to wait for a resource
* held by the GPU and so trigger a hangcheck. In the most
* pathological case, this will be upon memory starvation! To
* prevent this, we also queue the hangcheck from the retire
* worker.
*/
i915_queue_hangcheck(engine->i915);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
}
static void irq_enable(struct intel_engine_cs *engine)
{
drm/i915: Only apply one barrier after a breadcrumb interrupt is posted If we flag the seqno as potentially stale upon receiving an interrupt, we can use that information to reduce the frequency that we apply the heavyweight coherent seqno read (i.e. if we wake up a chain of waiters). v2: Use cmpxchg to replace READ_ONCE/WRITE_ONCE for more explicit control of the ordering wrt to interrupt generation and interrupt checking in the bottom-half. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-14-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:23 +08:00
/* Enabling the IRQ may miss the generation of the interrupt, but
* we still need to force the barrier before reading the seqno,
* just in case.
*/
drm/i915: Move breadcrumbs irq_posted up a level to engine In the next patch, we will use the irq_posted technique for another engine interrupt, rather than use two members for the atomic updates, we can use two bits of one instead. First, we need to update the breadcrumbs to use the new common engine->irq_posted. v2: Use set_bit() rather than __set_bit() to ensure atomicity with respect to other bits in the mask Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170124151805.26146-1-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
2017-01-24 23:18:05 +08:00
set_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
drm/i915: Move the get/put irq locking into the caller With only a single callsite for intel_engine_cs->irq_get and ->irq_put, we can reduce the code size by moving the common preamble into the caller, and we can also eliminate the reference counting. For completeness, as we are no longer doing reference counting on irq, rename the get/put vfunctions to enable/disable respectively and are able to review the use of posting reads. We only require the serialisation with hardware when enabling the interrupt (i.e. so we cannot miss an interrupt by going to sleep before the hardware truly enables it). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-18-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:27 +08:00
drm/i915: Convert breadcrumbs spinlock to be irqsafe The breadcrumbs are about to be used from within IRQ context sections (e.g. nouveau signals a fence from an interrupt handler causing us to submit a new request) and/or from bottom-half tasklets (i.e. intel_lrc_irq_handler), therefore we need to employ the irqsafe spinlock variants. For example, deferring the request submission to the intel_lrc_irq_handler generates this trace: [ 66.388639] ================================= [ 66.388650] [ INFO: inconsistent lock state ] [ 66.388663] 4.9.0-rc2+ #56 Not tainted [ 66.388672] --------------------------------- [ 66.388682] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. [ 66.388695] swapper/1/0 [HC0[0]:SC1[1]:HE0:SE0] takes: [ 66.388706] (&(&b->lock)->rlock){+.?...} , at: [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.388761] {SOFTIRQ-ON-W} state was registered at: [ 66.388772] [ 66.388783] [<ffffffff810bd842>] __lock_acquire+0x682/0x1870 [ 66.388795] [ 66.388803] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.388814] [ 66.388824] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.388835] [ 66.388845] [<ffffffff81401e41>] intel_engine_reset_breadcrumbs+0x21/0xb0 [ 66.388857] [ 66.388866] [<ffffffff81403ae7>] gen8_init_common_ring+0x67/0x100 [ 66.388878] [ 66.388887] [<ffffffff81403b92>] gen8_init_render_ring+0x12/0x60 [ 66.388903] [ 66.388912] [<ffffffff813f8707>] i915_gem_init_hw+0xf7/0x2a0 [ 66.388927] [ 66.388936] [<ffffffff813f899b>] i915_gem_init+0xbb/0xf0 [ 66.388950] [ 66.388959] [<ffffffff813b4980>] i915_driver_load+0x7e0/0x1330 [ 66.388978] [ 66.388988] [<ffffffff813c09d8>] i915_pci_probe+0x28/0x40 [ 66.389003] [ 66.389013] [<ffffffff812fa0db>] pci_device_probe+0x8b/0xf0 [ 66.389028] [ 66.389037] [<ffffffff8147737e>] driver_probe_device+0x21e/0x430 [ 66.389056] [ 66.389065] [<ffffffff8147766e>] __driver_attach+0xde/0xe0 [ 66.389080] [ 66.389090] [<ffffffff814751ad>] bus_for_each_dev+0x5d/0x90 [ 66.389105] [ 66.389113] [<ffffffff81477799>] driver_attach+0x19/0x20 [ 66.389134] [ 66.389144] [<ffffffff81475ced>] bus_add_driver+0x15d/0x260 [ 66.389159] [ 66.389168] [<ffffffff81477e3b>] driver_register+0x5b/0xd0 [ 66.389183] [ 66.389281] [<ffffffff812fa19b>] __pci_register_driver+0x5b/0x60 [ 66.389301] [ 66.389312] [<ffffffff81aed333>] i915_init+0x3e/0x45 [ 66.389326] [ 66.389336] [<ffffffff81ac2ffa>] do_one_initcall+0x8b/0x118 [ 66.389350] [ 66.389359] [<ffffffff81ac323a>] kernel_init_freeable+0x1b3/0x23b [ 66.389378] [ 66.389387] [<ffffffff8160fc39>] kernel_init+0x9/0x100 [ 66.389402] [ 66.389411] [<ffffffff816180e7>] ret_from_fork+0x27/0x40 [ 66.389426] irq event stamp: 315865 [ 66.389438] hardirqs last enabled at (315864): [<ffffffff816178f1>] _raw_spin_unlock_irqrestore+0x31/0x50 [ 66.389469] hardirqs last disabled at (315865): [<ffffffff816176b3>] _raw_spin_lock_irqsave+0x13/0x50 [ 66.389499] softirqs last enabled at (315818): [<ffffffff8107a04c>] _local_bh_enable+0x1c/0x50 [ 66.389530] softirqs last disabled at (315819): [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.389559] [ 66.389559] other info that might help us debug this: [ 66.389580] Possible unsafe locking scenario: [ 66.389580] [ 66.389598] CPU0 [ 66.389609] ---- [ 66.389620] lock(&(&b->lock)->rlock); [ 66.389650] <Interrupt> [ 66.389661] lock(&(&b->lock)->rlock); [ 66.389690] [ 66.389690] *** DEADLOCK *** [ 66.389690] [ 66.389715] 2 locks held by swapper/1/0: [ 66.389728] #0: (&(&tl->lock)->rlock){..-...}, at: [<ffffffff81403e01>] intel_lrc_irq_handler+0x201/0x3c0 [ 66.389785] #1: (&(&req->lock)->rlock/1){..-...}, at: [<ffffffff813fc0af>] __i915_gem_request_submit+0x8f/0x170 [ 66.389854] [ 66.389854] stack backtrace: [ 66.389959] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.0-rc2+ #56 [ 66.389976] Hardware name: / , BIOS PYBSWCEL.86A.0027.2015.0507.1758 05/07/2015 [ 66.389999] ffff88027fd03c58 ffffffff812beae5 ffff88027696e680 ffffffff822afe20 [ 66.390036] ffff88027fd03ca8 ffffffff810bb420 0000000000000001 0000000000000000 [ 66.390070] 0000000000000000 0000000000000006 0000000000000004 ffff88027696ee10 [ 66.390104] Call Trace: [ 66.390117] <IRQ> [ 66.390128] [<ffffffff812beae5>] dump_stack+0x68/0x93 [ 66.390147] [<ffffffff810bb420>] print_usage_bug+0x1d0/0x1e0 [ 66.390164] [<ffffffff810bb8a0>] mark_lock+0x470/0x4f0 [ 66.390181] [<ffffffff810ba9d0>] ? print_shortest_lock_dependencies+0x1b0/0x1b0 [ 66.390203] [<ffffffff810bd75d>] __lock_acquire+0x59d/0x1870 [ 66.390221] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.390237] [<ffffffff810bedbc>] ? lock_acquire+0x6c/0xb0 [ 66.390255] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390273] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.390291] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390309] [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.390327] [<ffffffff813fc170>] __i915_gem_request_submit+0x150/0x170 [ 66.390345] [<ffffffff81403e8b>] intel_lrc_irq_handler+0x28b/0x3c0 [ 66.390363] [<ffffffff81079d97>] tasklet_action+0x57/0xc0 [ 66.390380] [<ffffffff8107a249>] __do_softirq+0x119/0x240 [ 66.390396] [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.390414] [<ffffffff8101afd5>] do_IRQ+0x65/0x110 [ 66.390431] [<ffffffff81618806>] common_interrupt+0x86/0x86 [ 66.390446] <EOI> [ 66.390457] [<ffffffff814ec6d1>] ? cpuidle_enter_state+0x151/0x200 [ 66.390480] [<ffffffff814ec7a2>] cpuidle_enter+0x12/0x20 [ 66.390498] [<ffffffff810b639e>] call_cpuidle+0x1e/0x40 [ 66.390516] [<ffffffff810b65ae>] cpu_startup_entry+0x10e/0x1f0 [ 66.390534] [<ffffffff81036133>] start_secondary+0x103/0x130 (This is split out of the defer global seqno allocation patch due to realisation that we need a more complete conversion if we want to defer request submission even further.) v2: lockdep was warning about mixed SOFTIRQ contexts not HARDIRQ contexts so we only need to use spin_lock_bh and not disable interrupts. v3: We need full irq protection as we may be called from a third party interrupt handler (via fences). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161028125858.23563-32-chris@chris-wilson.co.uk
2016-10-28 20:58:55 +08:00
/* Caller disables interrupts */
spin_lock(&engine->i915->irq_lock);
drm/i915: Move the get/put irq locking into the caller With only a single callsite for intel_engine_cs->irq_get and ->irq_put, we can reduce the code size by moving the common preamble into the caller, and we can also eliminate the reference counting. For completeness, as we are no longer doing reference counting on irq, rename the get/put vfunctions to enable/disable respectively and are able to review the use of posting reads. We only require the serialisation with hardware when enabling the interrupt (i.e. so we cannot miss an interrupt by going to sleep before the hardware truly enables it). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-18-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:27 +08:00
engine->irq_enable(engine);
drm/i915: Convert breadcrumbs spinlock to be irqsafe The breadcrumbs are about to be used from within IRQ context sections (e.g. nouveau signals a fence from an interrupt handler causing us to submit a new request) and/or from bottom-half tasklets (i.e. intel_lrc_irq_handler), therefore we need to employ the irqsafe spinlock variants. For example, deferring the request submission to the intel_lrc_irq_handler generates this trace: [ 66.388639] ================================= [ 66.388650] [ INFO: inconsistent lock state ] [ 66.388663] 4.9.0-rc2+ #56 Not tainted [ 66.388672] --------------------------------- [ 66.388682] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. [ 66.388695] swapper/1/0 [HC0[0]:SC1[1]:HE0:SE0] takes: [ 66.388706] (&(&b->lock)->rlock){+.?...} , at: [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.388761] {SOFTIRQ-ON-W} state was registered at: [ 66.388772] [ 66.388783] [<ffffffff810bd842>] __lock_acquire+0x682/0x1870 [ 66.388795] [ 66.388803] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.388814] [ 66.388824] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.388835] [ 66.388845] [<ffffffff81401e41>] intel_engine_reset_breadcrumbs+0x21/0xb0 [ 66.388857] [ 66.388866] [<ffffffff81403ae7>] gen8_init_common_ring+0x67/0x100 [ 66.388878] [ 66.388887] [<ffffffff81403b92>] gen8_init_render_ring+0x12/0x60 [ 66.388903] [ 66.388912] [<ffffffff813f8707>] i915_gem_init_hw+0xf7/0x2a0 [ 66.388927] [ 66.388936] [<ffffffff813f899b>] i915_gem_init+0xbb/0xf0 [ 66.388950] [ 66.388959] [<ffffffff813b4980>] i915_driver_load+0x7e0/0x1330 [ 66.388978] [ 66.388988] [<ffffffff813c09d8>] i915_pci_probe+0x28/0x40 [ 66.389003] [ 66.389013] [<ffffffff812fa0db>] pci_device_probe+0x8b/0xf0 [ 66.389028] [ 66.389037] [<ffffffff8147737e>] driver_probe_device+0x21e/0x430 [ 66.389056] [ 66.389065] [<ffffffff8147766e>] __driver_attach+0xde/0xe0 [ 66.389080] [ 66.389090] [<ffffffff814751ad>] bus_for_each_dev+0x5d/0x90 [ 66.389105] [ 66.389113] [<ffffffff81477799>] driver_attach+0x19/0x20 [ 66.389134] [ 66.389144] [<ffffffff81475ced>] bus_add_driver+0x15d/0x260 [ 66.389159] [ 66.389168] [<ffffffff81477e3b>] driver_register+0x5b/0xd0 [ 66.389183] [ 66.389281] [<ffffffff812fa19b>] __pci_register_driver+0x5b/0x60 [ 66.389301] [ 66.389312] [<ffffffff81aed333>] i915_init+0x3e/0x45 [ 66.389326] [ 66.389336] [<ffffffff81ac2ffa>] do_one_initcall+0x8b/0x118 [ 66.389350] [ 66.389359] [<ffffffff81ac323a>] kernel_init_freeable+0x1b3/0x23b [ 66.389378] [ 66.389387] [<ffffffff8160fc39>] kernel_init+0x9/0x100 [ 66.389402] [ 66.389411] [<ffffffff816180e7>] ret_from_fork+0x27/0x40 [ 66.389426] irq event stamp: 315865 [ 66.389438] hardirqs last enabled at (315864): [<ffffffff816178f1>] _raw_spin_unlock_irqrestore+0x31/0x50 [ 66.389469] hardirqs last disabled at (315865): [<ffffffff816176b3>] _raw_spin_lock_irqsave+0x13/0x50 [ 66.389499] softirqs last enabled at (315818): [<ffffffff8107a04c>] _local_bh_enable+0x1c/0x50 [ 66.389530] softirqs last disabled at (315819): [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.389559] [ 66.389559] other info that might help us debug this: [ 66.389580] Possible unsafe locking scenario: [ 66.389580] [ 66.389598] CPU0 [ 66.389609] ---- [ 66.389620] lock(&(&b->lock)->rlock); [ 66.389650] <Interrupt> [ 66.389661] lock(&(&b->lock)->rlock); [ 66.389690] [ 66.389690] *** DEADLOCK *** [ 66.389690] [ 66.389715] 2 locks held by swapper/1/0: [ 66.389728] #0: (&(&tl->lock)->rlock){..-...}, at: [<ffffffff81403e01>] intel_lrc_irq_handler+0x201/0x3c0 [ 66.389785] #1: (&(&req->lock)->rlock/1){..-...}, at: [<ffffffff813fc0af>] __i915_gem_request_submit+0x8f/0x170 [ 66.389854] [ 66.389854] stack backtrace: [ 66.389959] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.0-rc2+ #56 [ 66.389976] Hardware name: / , BIOS PYBSWCEL.86A.0027.2015.0507.1758 05/07/2015 [ 66.389999] ffff88027fd03c58 ffffffff812beae5 ffff88027696e680 ffffffff822afe20 [ 66.390036] ffff88027fd03ca8 ffffffff810bb420 0000000000000001 0000000000000000 [ 66.390070] 0000000000000000 0000000000000006 0000000000000004 ffff88027696ee10 [ 66.390104] Call Trace: [ 66.390117] <IRQ> [ 66.390128] [<ffffffff812beae5>] dump_stack+0x68/0x93 [ 66.390147] [<ffffffff810bb420>] print_usage_bug+0x1d0/0x1e0 [ 66.390164] [<ffffffff810bb8a0>] mark_lock+0x470/0x4f0 [ 66.390181] [<ffffffff810ba9d0>] ? print_shortest_lock_dependencies+0x1b0/0x1b0 [ 66.390203] [<ffffffff810bd75d>] __lock_acquire+0x59d/0x1870 [ 66.390221] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.390237] [<ffffffff810bedbc>] ? lock_acquire+0x6c/0xb0 [ 66.390255] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390273] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.390291] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390309] [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.390327] [<ffffffff813fc170>] __i915_gem_request_submit+0x150/0x170 [ 66.390345] [<ffffffff81403e8b>] intel_lrc_irq_handler+0x28b/0x3c0 [ 66.390363] [<ffffffff81079d97>] tasklet_action+0x57/0xc0 [ 66.390380] [<ffffffff8107a249>] __do_softirq+0x119/0x240 [ 66.390396] [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.390414] [<ffffffff8101afd5>] do_IRQ+0x65/0x110 [ 66.390431] [<ffffffff81618806>] common_interrupt+0x86/0x86 [ 66.390446] <EOI> [ 66.390457] [<ffffffff814ec6d1>] ? cpuidle_enter_state+0x151/0x200 [ 66.390480] [<ffffffff814ec7a2>] cpuidle_enter+0x12/0x20 [ 66.390498] [<ffffffff810b639e>] call_cpuidle+0x1e/0x40 [ 66.390516] [<ffffffff810b65ae>] cpu_startup_entry+0x10e/0x1f0 [ 66.390534] [<ffffffff81036133>] start_secondary+0x103/0x130 (This is split out of the defer global seqno allocation patch due to realisation that we need a more complete conversion if we want to defer request submission even further.) v2: lockdep was warning about mixed SOFTIRQ contexts not HARDIRQ contexts so we only need to use spin_lock_bh and not disable interrupts. v3: We need full irq protection as we may be called from a third party interrupt handler (via fences). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161028125858.23563-32-chris@chris-wilson.co.uk
2016-10-28 20:58:55 +08:00
spin_unlock(&engine->i915->irq_lock);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
}
static void irq_disable(struct intel_engine_cs *engine)
{
drm/i915: Convert breadcrumbs spinlock to be irqsafe The breadcrumbs are about to be used from within IRQ context sections (e.g. nouveau signals a fence from an interrupt handler causing us to submit a new request) and/or from bottom-half tasklets (i.e. intel_lrc_irq_handler), therefore we need to employ the irqsafe spinlock variants. For example, deferring the request submission to the intel_lrc_irq_handler generates this trace: [ 66.388639] ================================= [ 66.388650] [ INFO: inconsistent lock state ] [ 66.388663] 4.9.0-rc2+ #56 Not tainted [ 66.388672] --------------------------------- [ 66.388682] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. [ 66.388695] swapper/1/0 [HC0[0]:SC1[1]:HE0:SE0] takes: [ 66.388706] (&(&b->lock)->rlock){+.?...} , at: [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.388761] {SOFTIRQ-ON-W} state was registered at: [ 66.388772] [ 66.388783] [<ffffffff810bd842>] __lock_acquire+0x682/0x1870 [ 66.388795] [ 66.388803] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.388814] [ 66.388824] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.388835] [ 66.388845] [<ffffffff81401e41>] intel_engine_reset_breadcrumbs+0x21/0xb0 [ 66.388857] [ 66.388866] [<ffffffff81403ae7>] gen8_init_common_ring+0x67/0x100 [ 66.388878] [ 66.388887] [<ffffffff81403b92>] gen8_init_render_ring+0x12/0x60 [ 66.388903] [ 66.388912] [<ffffffff813f8707>] i915_gem_init_hw+0xf7/0x2a0 [ 66.388927] [ 66.388936] [<ffffffff813f899b>] i915_gem_init+0xbb/0xf0 [ 66.388950] [ 66.388959] [<ffffffff813b4980>] i915_driver_load+0x7e0/0x1330 [ 66.388978] [ 66.388988] [<ffffffff813c09d8>] i915_pci_probe+0x28/0x40 [ 66.389003] [ 66.389013] [<ffffffff812fa0db>] pci_device_probe+0x8b/0xf0 [ 66.389028] [ 66.389037] [<ffffffff8147737e>] driver_probe_device+0x21e/0x430 [ 66.389056] [ 66.389065] [<ffffffff8147766e>] __driver_attach+0xde/0xe0 [ 66.389080] [ 66.389090] [<ffffffff814751ad>] bus_for_each_dev+0x5d/0x90 [ 66.389105] [ 66.389113] [<ffffffff81477799>] driver_attach+0x19/0x20 [ 66.389134] [ 66.389144] [<ffffffff81475ced>] bus_add_driver+0x15d/0x260 [ 66.389159] [ 66.389168] [<ffffffff81477e3b>] driver_register+0x5b/0xd0 [ 66.389183] [ 66.389281] [<ffffffff812fa19b>] __pci_register_driver+0x5b/0x60 [ 66.389301] [ 66.389312] [<ffffffff81aed333>] i915_init+0x3e/0x45 [ 66.389326] [ 66.389336] [<ffffffff81ac2ffa>] do_one_initcall+0x8b/0x118 [ 66.389350] [ 66.389359] [<ffffffff81ac323a>] kernel_init_freeable+0x1b3/0x23b [ 66.389378] [ 66.389387] [<ffffffff8160fc39>] kernel_init+0x9/0x100 [ 66.389402] [ 66.389411] [<ffffffff816180e7>] ret_from_fork+0x27/0x40 [ 66.389426] irq event stamp: 315865 [ 66.389438] hardirqs last enabled at (315864): [<ffffffff816178f1>] _raw_spin_unlock_irqrestore+0x31/0x50 [ 66.389469] hardirqs last disabled at (315865): [<ffffffff816176b3>] _raw_spin_lock_irqsave+0x13/0x50 [ 66.389499] softirqs last enabled at (315818): [<ffffffff8107a04c>] _local_bh_enable+0x1c/0x50 [ 66.389530] softirqs last disabled at (315819): [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.389559] [ 66.389559] other info that might help us debug this: [ 66.389580] Possible unsafe locking scenario: [ 66.389580] [ 66.389598] CPU0 [ 66.389609] ---- [ 66.389620] lock(&(&b->lock)->rlock); [ 66.389650] <Interrupt> [ 66.389661] lock(&(&b->lock)->rlock); [ 66.389690] [ 66.389690] *** DEADLOCK *** [ 66.389690] [ 66.389715] 2 locks held by swapper/1/0: [ 66.389728] #0: (&(&tl->lock)->rlock){..-...}, at: [<ffffffff81403e01>] intel_lrc_irq_handler+0x201/0x3c0 [ 66.389785] #1: (&(&req->lock)->rlock/1){..-...}, at: [<ffffffff813fc0af>] __i915_gem_request_submit+0x8f/0x170 [ 66.389854] [ 66.389854] stack backtrace: [ 66.389959] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.0-rc2+ #56 [ 66.389976] Hardware name: / , BIOS PYBSWCEL.86A.0027.2015.0507.1758 05/07/2015 [ 66.389999] ffff88027fd03c58 ffffffff812beae5 ffff88027696e680 ffffffff822afe20 [ 66.390036] ffff88027fd03ca8 ffffffff810bb420 0000000000000001 0000000000000000 [ 66.390070] 0000000000000000 0000000000000006 0000000000000004 ffff88027696ee10 [ 66.390104] Call Trace: [ 66.390117] <IRQ> [ 66.390128] [<ffffffff812beae5>] dump_stack+0x68/0x93 [ 66.390147] [<ffffffff810bb420>] print_usage_bug+0x1d0/0x1e0 [ 66.390164] [<ffffffff810bb8a0>] mark_lock+0x470/0x4f0 [ 66.390181] [<ffffffff810ba9d0>] ? print_shortest_lock_dependencies+0x1b0/0x1b0 [ 66.390203] [<ffffffff810bd75d>] __lock_acquire+0x59d/0x1870 [ 66.390221] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.390237] [<ffffffff810bedbc>] ? lock_acquire+0x6c/0xb0 [ 66.390255] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390273] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.390291] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390309] [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.390327] [<ffffffff813fc170>] __i915_gem_request_submit+0x150/0x170 [ 66.390345] [<ffffffff81403e8b>] intel_lrc_irq_handler+0x28b/0x3c0 [ 66.390363] [<ffffffff81079d97>] tasklet_action+0x57/0xc0 [ 66.390380] [<ffffffff8107a249>] __do_softirq+0x119/0x240 [ 66.390396] [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.390414] [<ffffffff8101afd5>] do_IRQ+0x65/0x110 [ 66.390431] [<ffffffff81618806>] common_interrupt+0x86/0x86 [ 66.390446] <EOI> [ 66.390457] [<ffffffff814ec6d1>] ? cpuidle_enter_state+0x151/0x200 [ 66.390480] [<ffffffff814ec7a2>] cpuidle_enter+0x12/0x20 [ 66.390498] [<ffffffff810b639e>] call_cpuidle+0x1e/0x40 [ 66.390516] [<ffffffff810b65ae>] cpu_startup_entry+0x10e/0x1f0 [ 66.390534] [<ffffffff81036133>] start_secondary+0x103/0x130 (This is split out of the defer global seqno allocation patch due to realisation that we need a more complete conversion if we want to defer request submission even further.) v2: lockdep was warning about mixed SOFTIRQ contexts not HARDIRQ contexts so we only need to use spin_lock_bh and not disable interrupts. v3: We need full irq protection as we may be called from a third party interrupt handler (via fences). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161028125858.23563-32-chris@chris-wilson.co.uk
2016-10-28 20:58:55 +08:00
/* Caller disables interrupts */
spin_lock(&engine->i915->irq_lock);
drm/i915: Move the get/put irq locking into the caller With only a single callsite for intel_engine_cs->irq_get and ->irq_put, we can reduce the code size by moving the common preamble into the caller, and we can also eliminate the reference counting. For completeness, as we are no longer doing reference counting on irq, rename the get/put vfunctions to enable/disable respectively and are able to review the use of posting reads. We only require the serialisation with hardware when enabling the interrupt (i.e. so we cannot miss an interrupt by going to sleep before the hardware truly enables it). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-18-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:27 +08:00
engine->irq_disable(engine);
drm/i915: Convert breadcrumbs spinlock to be irqsafe The breadcrumbs are about to be used from within IRQ context sections (e.g. nouveau signals a fence from an interrupt handler causing us to submit a new request) and/or from bottom-half tasklets (i.e. intel_lrc_irq_handler), therefore we need to employ the irqsafe spinlock variants. For example, deferring the request submission to the intel_lrc_irq_handler generates this trace: [ 66.388639] ================================= [ 66.388650] [ INFO: inconsistent lock state ] [ 66.388663] 4.9.0-rc2+ #56 Not tainted [ 66.388672] --------------------------------- [ 66.388682] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. [ 66.388695] swapper/1/0 [HC0[0]:SC1[1]:HE0:SE0] takes: [ 66.388706] (&(&b->lock)->rlock){+.?...} , at: [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.388761] {SOFTIRQ-ON-W} state was registered at: [ 66.388772] [ 66.388783] [<ffffffff810bd842>] __lock_acquire+0x682/0x1870 [ 66.388795] [ 66.388803] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.388814] [ 66.388824] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.388835] [ 66.388845] [<ffffffff81401e41>] intel_engine_reset_breadcrumbs+0x21/0xb0 [ 66.388857] [ 66.388866] [<ffffffff81403ae7>] gen8_init_common_ring+0x67/0x100 [ 66.388878] [ 66.388887] [<ffffffff81403b92>] gen8_init_render_ring+0x12/0x60 [ 66.388903] [ 66.388912] [<ffffffff813f8707>] i915_gem_init_hw+0xf7/0x2a0 [ 66.388927] [ 66.388936] [<ffffffff813f899b>] i915_gem_init+0xbb/0xf0 [ 66.388950] [ 66.388959] [<ffffffff813b4980>] i915_driver_load+0x7e0/0x1330 [ 66.388978] [ 66.388988] [<ffffffff813c09d8>] i915_pci_probe+0x28/0x40 [ 66.389003] [ 66.389013] [<ffffffff812fa0db>] pci_device_probe+0x8b/0xf0 [ 66.389028] [ 66.389037] [<ffffffff8147737e>] driver_probe_device+0x21e/0x430 [ 66.389056] [ 66.389065] [<ffffffff8147766e>] __driver_attach+0xde/0xe0 [ 66.389080] [ 66.389090] [<ffffffff814751ad>] bus_for_each_dev+0x5d/0x90 [ 66.389105] [ 66.389113] [<ffffffff81477799>] driver_attach+0x19/0x20 [ 66.389134] [ 66.389144] [<ffffffff81475ced>] bus_add_driver+0x15d/0x260 [ 66.389159] [ 66.389168] [<ffffffff81477e3b>] driver_register+0x5b/0xd0 [ 66.389183] [ 66.389281] [<ffffffff812fa19b>] __pci_register_driver+0x5b/0x60 [ 66.389301] [ 66.389312] [<ffffffff81aed333>] i915_init+0x3e/0x45 [ 66.389326] [ 66.389336] [<ffffffff81ac2ffa>] do_one_initcall+0x8b/0x118 [ 66.389350] [ 66.389359] [<ffffffff81ac323a>] kernel_init_freeable+0x1b3/0x23b [ 66.389378] [ 66.389387] [<ffffffff8160fc39>] kernel_init+0x9/0x100 [ 66.389402] [ 66.389411] [<ffffffff816180e7>] ret_from_fork+0x27/0x40 [ 66.389426] irq event stamp: 315865 [ 66.389438] hardirqs last enabled at (315864): [<ffffffff816178f1>] _raw_spin_unlock_irqrestore+0x31/0x50 [ 66.389469] hardirqs last disabled at (315865): [<ffffffff816176b3>] _raw_spin_lock_irqsave+0x13/0x50 [ 66.389499] softirqs last enabled at (315818): [<ffffffff8107a04c>] _local_bh_enable+0x1c/0x50 [ 66.389530] softirqs last disabled at (315819): [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.389559] [ 66.389559] other info that might help us debug this: [ 66.389580] Possible unsafe locking scenario: [ 66.389580] [ 66.389598] CPU0 [ 66.389609] ---- [ 66.389620] lock(&(&b->lock)->rlock); [ 66.389650] <Interrupt> [ 66.389661] lock(&(&b->lock)->rlock); [ 66.389690] [ 66.389690] *** DEADLOCK *** [ 66.389690] [ 66.389715] 2 locks held by swapper/1/0: [ 66.389728] #0: (&(&tl->lock)->rlock){..-...}, at: [<ffffffff81403e01>] intel_lrc_irq_handler+0x201/0x3c0 [ 66.389785] #1: (&(&req->lock)->rlock/1){..-...}, at: [<ffffffff813fc0af>] __i915_gem_request_submit+0x8f/0x170 [ 66.389854] [ 66.389854] stack backtrace: [ 66.389959] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.0-rc2+ #56 [ 66.389976] Hardware name: / , BIOS PYBSWCEL.86A.0027.2015.0507.1758 05/07/2015 [ 66.389999] ffff88027fd03c58 ffffffff812beae5 ffff88027696e680 ffffffff822afe20 [ 66.390036] ffff88027fd03ca8 ffffffff810bb420 0000000000000001 0000000000000000 [ 66.390070] 0000000000000000 0000000000000006 0000000000000004 ffff88027696ee10 [ 66.390104] Call Trace: [ 66.390117] <IRQ> [ 66.390128] [<ffffffff812beae5>] dump_stack+0x68/0x93 [ 66.390147] [<ffffffff810bb420>] print_usage_bug+0x1d0/0x1e0 [ 66.390164] [<ffffffff810bb8a0>] mark_lock+0x470/0x4f0 [ 66.390181] [<ffffffff810ba9d0>] ? print_shortest_lock_dependencies+0x1b0/0x1b0 [ 66.390203] [<ffffffff810bd75d>] __lock_acquire+0x59d/0x1870 [ 66.390221] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.390237] [<ffffffff810bedbc>] ? lock_acquire+0x6c/0xb0 [ 66.390255] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390273] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.390291] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390309] [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.390327] [<ffffffff813fc170>] __i915_gem_request_submit+0x150/0x170 [ 66.390345] [<ffffffff81403e8b>] intel_lrc_irq_handler+0x28b/0x3c0 [ 66.390363] [<ffffffff81079d97>] tasklet_action+0x57/0xc0 [ 66.390380] [<ffffffff8107a249>] __do_softirq+0x119/0x240 [ 66.390396] [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.390414] [<ffffffff8101afd5>] do_IRQ+0x65/0x110 [ 66.390431] [<ffffffff81618806>] common_interrupt+0x86/0x86 [ 66.390446] <EOI> [ 66.390457] [<ffffffff814ec6d1>] ? cpuidle_enter_state+0x151/0x200 [ 66.390480] [<ffffffff814ec7a2>] cpuidle_enter+0x12/0x20 [ 66.390498] [<ffffffff810b639e>] call_cpuidle+0x1e/0x40 [ 66.390516] [<ffffffff810b65ae>] cpu_startup_entry+0x10e/0x1f0 [ 66.390534] [<ffffffff81036133>] start_secondary+0x103/0x130 (This is split out of the defer global seqno allocation patch due to realisation that we need a more complete conversion if we want to defer request submission even further.) v2: lockdep was warning about mixed SOFTIRQ contexts not HARDIRQ contexts so we only need to use spin_lock_bh and not disable interrupts. v3: We need full irq protection as we may be called from a third party interrupt handler (via fences). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161028125858.23563-32-chris@chris-wilson.co.uk
2016-10-28 20:58:55 +08:00
spin_unlock(&engine->i915->irq_lock);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
}
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
void __intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
lockdep_assert_held(&b->irq_lock);
drm/i915: Wake up all waiters before idling When we idle, we wakeup the first waiter (checking to see if it missed an earlier wakeup) and disarm the breadcrumbs. However, we now assert that there are no waiter when the interrupt is disabled, triggering an assert if there were multiple waiters when we idled. [ 420.842275] invalid opcode: 0000 [#1] PREEMPT SMP [ 420.842285] Modules linked in: vgem snd_hda_codec_realtek x86_pkg_temp_thermal snd_hda_codec_generic intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_hda_intel snd_hda_codec snd_hwdep mei_me snd_hda_core mei snd_pcm lpc_ich i915 r8169 mii prime_numbers [ 420.842357] CPU: 4 PID: 8714 Comm: kms_pipe_crc_ba Tainted: G U W 4.10.0-CI-CI_DRM_2280+ #1 [ 420.842377] Hardware name: Hewlett-Packard HP Pro 3500 Series/2ABF, BIOS 8.11 10/24/2012 [ 420.842395] task: ffff880117ddce40 task.stack: ffffc90001114000 [ 420.842439] RIP: 0010:__intel_engine_remove_wait+0x1f4/0x200 [i915] [ 420.842454] RSP: 0018:ffffc90001117b18 EFLAGS: 00010046 [ 420.842467] RAX: 0000000000000000 RBX: ffff88010c25c2a8 RCX: 0000000000000001 [ 420.842481] RDX: 0000000000000001 RSI: 00000000ffffffff RDI: ffffc90001117c50 [ 420.842495] RBP: ffffc90001117b58 R08: 0000000011e52352 R09: c4d16acc00000000 [ 420.842511] R10: ffffffff82789eb0 R11: ffff880117ddce40 R12: ffffc90001117c50 [ 420.842525] R13: ffffc90001117c50 R14: 0000000000000078 R15: 0000000000000000 [ 420.842540] FS: 00007fe47dda0a40(0000) GS:ffff88011fb00000(0000) knlGS:0000000000000000 [ 420.842559] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 420.842571] CR2: 00007fd6c0a2cec4 CR3: 000000010a5e5000 CR4: 00000000001406e0 [ 420.842586] Call Trace: [ 420.842595] ? do_raw_spin_lock+0xad/0xb0 [ 420.842635] intel_engine_remove_wait.part.3+0x26/0x40 [i915] [ 420.842678] intel_engine_remove_wait+0xe/0x20 [i915] [ 420.842721] i915_wait_request+0x4f0/0x8c0 [i915] [ 420.842736] ? wake_up_q+0x70/0x70 [ 420.842747] ? wake_up_q+0x70/0x70 [ 420.842787] i915_gem_object_wait_fence+0x7d/0x1a0 [i915] [ 420.842829] i915_gem_object_wait+0x30d/0x520 [i915] [ 420.842842] ? __this_cpu_preempt_check+0x13/0x20 [ 420.842884] i915_gem_wait_ioctl+0x12e/0x2e0 [i915] [ 420.842924] ? i915_gem_wait_ioctl+0x22/0x2e0 [i915] [ 420.842939] drm_ioctl+0x200/0x450 [ 420.842976] ? i915_gem_set_wedged+0x90/0x90 [i915] [ 420.842993] do_vfs_ioctl+0x90/0x6e0 [ 420.843003] ? entry_SYSCALL_64_fastpath+0x5/0xb1 [ 420.843017] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843030] ? trace_hardirqs_on_caller+0xe7/0x200 [ 420.843042] SyS_ioctl+0x3c/0x70 [ 420.843054] entry_SYSCALL_64_fastpath+0x1c/0xb1 [ 420.843065] RIP: 0033:0x7fe47c4b9357 [ 420.843075] RSP: 002b:00007ffc3c0633c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 420.843094] RAX: ffffffffffffffda RBX: ffffffff81482393 RCX: 00007fe47c4b9357 [ 420.843109] RDX: 00007ffc3c063400 RSI: 00000000c010646c RDI: 0000000000000004 [ 420.843123] RBP: ffffc90001117f88 R08: 0000000000000008 R09: 0000000000000000 [ 420.843137] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 [ 420.843151] R13: 0000000000000004 R14: 00000000c010646c R15: 0000000000000000 [ 420.843168] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843180] Code: 81 48 c7 c1 40 6a 16 a0 48 c7 c2 47 29 15 a0 be 17 01 00 00 48 c7 c7 10 6a 16 a0 e8 c7 ea fe e0 e9 5d ff ff ff 0f 0b 0f 0b 0f 0b <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 e8 67 41 7e e1 [ 420.843325] RIP: __intel_engine_remove_wait+0x1f4/0x200 [i915] RSP: ffffc90001117b18 Fixes: b66255f0f779 ("drm/i915: Refactor wakeup of the next breadcrumb waiter") Fixes: 67b807a89230 ("drm/i915: Delay disabling the user interrupt for breadcrumbs") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170306092916.11623-2-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
2017-03-06 17:29:15 +08:00
GEM_BUG_ON(b->irq_wait);
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
if (b->irq_enabled) {
irq_disable(engine);
b->irq_enabled = false;
}
b->irq_armed = false;
}
void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915/breadcrumbs: Disable interrupt bottom-half first on idling Before walking the rbtree of waiters (marking them as complete and waking them), decouple the interrupt handler. This prevents a race between the missed waiter waking up and removing its intel_wait (which skips checking the lock) and the interrupt handler dereferencing the intel_wait. (Though we do not expect to encounter waiters during idle!) Fixes: e1c0c91bdaec ("drm/i915: Wake up all waiters before idling") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-3-chris@chris-wilson.co.uk
2017-03-16 05:07:24 +08:00
struct intel_wait *wait, *n, *first;
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
if (!b->irq_armed)
return;
/* We only disarm the irq when we are idle (all requests completed),
drm/i915: Wake up all waiters before idling When we idle, we wakeup the first waiter (checking to see if it missed an earlier wakeup) and disarm the breadcrumbs. However, we now assert that there are no waiter when the interrupt is disabled, triggering an assert if there were multiple waiters when we idled. [ 420.842275] invalid opcode: 0000 [#1] PREEMPT SMP [ 420.842285] Modules linked in: vgem snd_hda_codec_realtek x86_pkg_temp_thermal snd_hda_codec_generic intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_hda_intel snd_hda_codec snd_hwdep mei_me snd_hda_core mei snd_pcm lpc_ich i915 r8169 mii prime_numbers [ 420.842357] CPU: 4 PID: 8714 Comm: kms_pipe_crc_ba Tainted: G U W 4.10.0-CI-CI_DRM_2280+ #1 [ 420.842377] Hardware name: Hewlett-Packard HP Pro 3500 Series/2ABF, BIOS 8.11 10/24/2012 [ 420.842395] task: ffff880117ddce40 task.stack: ffffc90001114000 [ 420.842439] RIP: 0010:__intel_engine_remove_wait+0x1f4/0x200 [i915] [ 420.842454] RSP: 0018:ffffc90001117b18 EFLAGS: 00010046 [ 420.842467] RAX: 0000000000000000 RBX: ffff88010c25c2a8 RCX: 0000000000000001 [ 420.842481] RDX: 0000000000000001 RSI: 00000000ffffffff RDI: ffffc90001117c50 [ 420.842495] RBP: ffffc90001117b58 R08: 0000000011e52352 R09: c4d16acc00000000 [ 420.842511] R10: ffffffff82789eb0 R11: ffff880117ddce40 R12: ffffc90001117c50 [ 420.842525] R13: ffffc90001117c50 R14: 0000000000000078 R15: 0000000000000000 [ 420.842540] FS: 00007fe47dda0a40(0000) GS:ffff88011fb00000(0000) knlGS:0000000000000000 [ 420.842559] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 420.842571] CR2: 00007fd6c0a2cec4 CR3: 000000010a5e5000 CR4: 00000000001406e0 [ 420.842586] Call Trace: [ 420.842595] ? do_raw_spin_lock+0xad/0xb0 [ 420.842635] intel_engine_remove_wait.part.3+0x26/0x40 [i915] [ 420.842678] intel_engine_remove_wait+0xe/0x20 [i915] [ 420.842721] i915_wait_request+0x4f0/0x8c0 [i915] [ 420.842736] ? wake_up_q+0x70/0x70 [ 420.842747] ? wake_up_q+0x70/0x70 [ 420.842787] i915_gem_object_wait_fence+0x7d/0x1a0 [i915] [ 420.842829] i915_gem_object_wait+0x30d/0x520 [i915] [ 420.842842] ? __this_cpu_preempt_check+0x13/0x20 [ 420.842884] i915_gem_wait_ioctl+0x12e/0x2e0 [i915] [ 420.842924] ? i915_gem_wait_ioctl+0x22/0x2e0 [i915] [ 420.842939] drm_ioctl+0x200/0x450 [ 420.842976] ? i915_gem_set_wedged+0x90/0x90 [i915] [ 420.842993] do_vfs_ioctl+0x90/0x6e0 [ 420.843003] ? entry_SYSCALL_64_fastpath+0x5/0xb1 [ 420.843017] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843030] ? trace_hardirqs_on_caller+0xe7/0x200 [ 420.843042] SyS_ioctl+0x3c/0x70 [ 420.843054] entry_SYSCALL_64_fastpath+0x1c/0xb1 [ 420.843065] RIP: 0033:0x7fe47c4b9357 [ 420.843075] RSP: 002b:00007ffc3c0633c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 420.843094] RAX: ffffffffffffffda RBX: ffffffff81482393 RCX: 00007fe47c4b9357 [ 420.843109] RDX: 00007ffc3c063400 RSI: 00000000c010646c RDI: 0000000000000004 [ 420.843123] RBP: ffffc90001117f88 R08: 0000000000000008 R09: 0000000000000000 [ 420.843137] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 [ 420.843151] R13: 0000000000000004 R14: 00000000c010646c R15: 0000000000000000 [ 420.843168] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843180] Code: 81 48 c7 c1 40 6a 16 a0 48 c7 c2 47 29 15 a0 be 17 01 00 00 48 c7 c7 10 6a 16 a0 e8 c7 ea fe e0 e9 5d ff ff ff 0f 0b 0f 0b 0f 0b <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 e8 67 41 7e e1 [ 420.843325] RIP: __intel_engine_remove_wait+0x1f4/0x200 [i915] RSP: ffffc90001117b18 Fixes: b66255f0f779 ("drm/i915: Refactor wakeup of the next breadcrumb waiter") Fixes: 67b807a89230 ("drm/i915: Delay disabling the user interrupt for breadcrumbs") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170306092916.11623-2-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
2017-03-06 17:29:15 +08:00
* so if the bottom-half remains asleep, it missed the request
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
* completion.
*/
drm/i915: Wake up all waiters before idling When we idle, we wakeup the first waiter (checking to see if it missed an earlier wakeup) and disarm the breadcrumbs. However, we now assert that there are no waiter when the interrupt is disabled, triggering an assert if there were multiple waiters when we idled. [ 420.842275] invalid opcode: 0000 [#1] PREEMPT SMP [ 420.842285] Modules linked in: vgem snd_hda_codec_realtek x86_pkg_temp_thermal snd_hda_codec_generic intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_hda_intel snd_hda_codec snd_hwdep mei_me snd_hda_core mei snd_pcm lpc_ich i915 r8169 mii prime_numbers [ 420.842357] CPU: 4 PID: 8714 Comm: kms_pipe_crc_ba Tainted: G U W 4.10.0-CI-CI_DRM_2280+ #1 [ 420.842377] Hardware name: Hewlett-Packard HP Pro 3500 Series/2ABF, BIOS 8.11 10/24/2012 [ 420.842395] task: ffff880117ddce40 task.stack: ffffc90001114000 [ 420.842439] RIP: 0010:__intel_engine_remove_wait+0x1f4/0x200 [i915] [ 420.842454] RSP: 0018:ffffc90001117b18 EFLAGS: 00010046 [ 420.842467] RAX: 0000000000000000 RBX: ffff88010c25c2a8 RCX: 0000000000000001 [ 420.842481] RDX: 0000000000000001 RSI: 00000000ffffffff RDI: ffffc90001117c50 [ 420.842495] RBP: ffffc90001117b58 R08: 0000000011e52352 R09: c4d16acc00000000 [ 420.842511] R10: ffffffff82789eb0 R11: ffff880117ddce40 R12: ffffc90001117c50 [ 420.842525] R13: ffffc90001117c50 R14: 0000000000000078 R15: 0000000000000000 [ 420.842540] FS: 00007fe47dda0a40(0000) GS:ffff88011fb00000(0000) knlGS:0000000000000000 [ 420.842559] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 420.842571] CR2: 00007fd6c0a2cec4 CR3: 000000010a5e5000 CR4: 00000000001406e0 [ 420.842586] Call Trace: [ 420.842595] ? do_raw_spin_lock+0xad/0xb0 [ 420.842635] intel_engine_remove_wait.part.3+0x26/0x40 [i915] [ 420.842678] intel_engine_remove_wait+0xe/0x20 [i915] [ 420.842721] i915_wait_request+0x4f0/0x8c0 [i915] [ 420.842736] ? wake_up_q+0x70/0x70 [ 420.842747] ? wake_up_q+0x70/0x70 [ 420.842787] i915_gem_object_wait_fence+0x7d/0x1a0 [i915] [ 420.842829] i915_gem_object_wait+0x30d/0x520 [i915] [ 420.842842] ? __this_cpu_preempt_check+0x13/0x20 [ 420.842884] i915_gem_wait_ioctl+0x12e/0x2e0 [i915] [ 420.842924] ? i915_gem_wait_ioctl+0x22/0x2e0 [i915] [ 420.842939] drm_ioctl+0x200/0x450 [ 420.842976] ? i915_gem_set_wedged+0x90/0x90 [i915] [ 420.842993] do_vfs_ioctl+0x90/0x6e0 [ 420.843003] ? entry_SYSCALL_64_fastpath+0x5/0xb1 [ 420.843017] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843030] ? trace_hardirqs_on_caller+0xe7/0x200 [ 420.843042] SyS_ioctl+0x3c/0x70 [ 420.843054] entry_SYSCALL_64_fastpath+0x1c/0xb1 [ 420.843065] RIP: 0033:0x7fe47c4b9357 [ 420.843075] RSP: 002b:00007ffc3c0633c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 420.843094] RAX: ffffffffffffffda RBX: ffffffff81482393 RCX: 00007fe47c4b9357 [ 420.843109] RDX: 00007ffc3c063400 RSI: 00000000c010646c RDI: 0000000000000004 [ 420.843123] RBP: ffffc90001117f88 R08: 0000000000000008 R09: 0000000000000000 [ 420.843137] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 [ 420.843151] R13: 0000000000000004 R14: 00000000c010646c R15: 0000000000000000 [ 420.843168] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843180] Code: 81 48 c7 c1 40 6a 16 a0 48 c7 c2 47 29 15 a0 be 17 01 00 00 48 c7 c7 10 6a 16 a0 e8 c7 ea fe e0 e9 5d ff ff ff 0f 0b 0f 0b 0f 0b <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 e8 67 41 7e e1 [ 420.843325] RIP: __intel_engine_remove_wait+0x1f4/0x200 [i915] RSP: ffffc90001117b18 Fixes: b66255f0f779 ("drm/i915: Refactor wakeup of the next breadcrumb waiter") Fixes: 67b807a89230 ("drm/i915: Delay disabling the user interrupt for breadcrumbs") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170306092916.11623-2-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
2017-03-06 17:29:15 +08:00
spin_lock_irq(&b->rb_lock);
drm/i915/breadcrumbs: Disable interrupt bottom-half first on idling Before walking the rbtree of waiters (marking them as complete and waking them), decouple the interrupt handler. This prevents a race between the missed waiter waking up and removing its intel_wait (which skips checking the lock) and the interrupt handler dereferencing the intel_wait. (Though we do not expect to encounter waiters during idle!) Fixes: e1c0c91bdaec ("drm/i915: Wake up all waiters before idling") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-3-chris@chris-wilson.co.uk
2017-03-16 05:07:24 +08:00
spin_lock(&b->irq_lock);
first = fetch_and_zero(&b->irq_wait);
__intel_engine_disarm_breadcrumbs(engine);
spin_unlock(&b->irq_lock);
drm/i915: Wake up all waiters before idling When we idle, we wakeup the first waiter (checking to see if it missed an earlier wakeup) and disarm the breadcrumbs. However, we now assert that there are no waiter when the interrupt is disabled, triggering an assert if there were multiple waiters when we idled. [ 420.842275] invalid opcode: 0000 [#1] PREEMPT SMP [ 420.842285] Modules linked in: vgem snd_hda_codec_realtek x86_pkg_temp_thermal snd_hda_codec_generic intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_hda_intel snd_hda_codec snd_hwdep mei_me snd_hda_core mei snd_pcm lpc_ich i915 r8169 mii prime_numbers [ 420.842357] CPU: 4 PID: 8714 Comm: kms_pipe_crc_ba Tainted: G U W 4.10.0-CI-CI_DRM_2280+ #1 [ 420.842377] Hardware name: Hewlett-Packard HP Pro 3500 Series/2ABF, BIOS 8.11 10/24/2012 [ 420.842395] task: ffff880117ddce40 task.stack: ffffc90001114000 [ 420.842439] RIP: 0010:__intel_engine_remove_wait+0x1f4/0x200 [i915] [ 420.842454] RSP: 0018:ffffc90001117b18 EFLAGS: 00010046 [ 420.842467] RAX: 0000000000000000 RBX: ffff88010c25c2a8 RCX: 0000000000000001 [ 420.842481] RDX: 0000000000000001 RSI: 00000000ffffffff RDI: ffffc90001117c50 [ 420.842495] RBP: ffffc90001117b58 R08: 0000000011e52352 R09: c4d16acc00000000 [ 420.842511] R10: ffffffff82789eb0 R11: ffff880117ddce40 R12: ffffc90001117c50 [ 420.842525] R13: ffffc90001117c50 R14: 0000000000000078 R15: 0000000000000000 [ 420.842540] FS: 00007fe47dda0a40(0000) GS:ffff88011fb00000(0000) knlGS:0000000000000000 [ 420.842559] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 420.842571] CR2: 00007fd6c0a2cec4 CR3: 000000010a5e5000 CR4: 00000000001406e0 [ 420.842586] Call Trace: [ 420.842595] ? do_raw_spin_lock+0xad/0xb0 [ 420.842635] intel_engine_remove_wait.part.3+0x26/0x40 [i915] [ 420.842678] intel_engine_remove_wait+0xe/0x20 [i915] [ 420.842721] i915_wait_request+0x4f0/0x8c0 [i915] [ 420.842736] ? wake_up_q+0x70/0x70 [ 420.842747] ? wake_up_q+0x70/0x70 [ 420.842787] i915_gem_object_wait_fence+0x7d/0x1a0 [i915] [ 420.842829] i915_gem_object_wait+0x30d/0x520 [i915] [ 420.842842] ? __this_cpu_preempt_check+0x13/0x20 [ 420.842884] i915_gem_wait_ioctl+0x12e/0x2e0 [i915] [ 420.842924] ? i915_gem_wait_ioctl+0x22/0x2e0 [i915] [ 420.842939] drm_ioctl+0x200/0x450 [ 420.842976] ? i915_gem_set_wedged+0x90/0x90 [i915] [ 420.842993] do_vfs_ioctl+0x90/0x6e0 [ 420.843003] ? entry_SYSCALL_64_fastpath+0x5/0xb1 [ 420.843017] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843030] ? trace_hardirqs_on_caller+0xe7/0x200 [ 420.843042] SyS_ioctl+0x3c/0x70 [ 420.843054] entry_SYSCALL_64_fastpath+0x1c/0xb1 [ 420.843065] RIP: 0033:0x7fe47c4b9357 [ 420.843075] RSP: 002b:00007ffc3c0633c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 420.843094] RAX: ffffffffffffffda RBX: ffffffff81482393 RCX: 00007fe47c4b9357 [ 420.843109] RDX: 00007ffc3c063400 RSI: 00000000c010646c RDI: 0000000000000004 [ 420.843123] RBP: ffffc90001117f88 R08: 0000000000000008 R09: 0000000000000000 [ 420.843137] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 [ 420.843151] R13: 0000000000000004 R14: 00000000c010646c R15: 0000000000000000 [ 420.843168] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843180] Code: 81 48 c7 c1 40 6a 16 a0 48 c7 c2 47 29 15 a0 be 17 01 00 00 48 c7 c7 10 6a 16 a0 e8 c7 ea fe e0 e9 5d ff ff ff 0f 0b 0f 0b 0f 0b <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 e8 67 41 7e e1 [ 420.843325] RIP: __intel_engine_remove_wait+0x1f4/0x200 [i915] RSP: ffffc90001117b18 Fixes: b66255f0f779 ("drm/i915: Refactor wakeup of the next breadcrumb waiter") Fixes: 67b807a89230 ("drm/i915: Delay disabling the user interrupt for breadcrumbs") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170306092916.11623-2-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
2017-03-06 17:29:15 +08:00
rbtree_postorder_for_each_entry_safe(wait, n, &b->waiters, node) {
RB_CLEAR_NODE(&wait->node);
drm/i915/breadcrumbs: Disable interrupt bottom-half first on idling Before walking the rbtree of waiters (marking them as complete and waking them), decouple the interrupt handler. This prevents a race between the missed waiter waking up and removing its intel_wait (which skips checking the lock) and the interrupt handler dereferencing the intel_wait. (Though we do not expect to encounter waiters during idle!) Fixes: e1c0c91bdaec ("drm/i915: Wake up all waiters before idling") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-3-chris@chris-wilson.co.uk
2017-03-16 05:07:24 +08:00
if (wake_up_process(wait->tsk) && wait == first)
drm/i915: Wake up all waiters before idling When we idle, we wakeup the first waiter (checking to see if it missed an earlier wakeup) and disarm the breadcrumbs. However, we now assert that there are no waiter when the interrupt is disabled, triggering an assert if there were multiple waiters when we idled. [ 420.842275] invalid opcode: 0000 [#1] PREEMPT SMP [ 420.842285] Modules linked in: vgem snd_hda_codec_realtek x86_pkg_temp_thermal snd_hda_codec_generic intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_hda_intel snd_hda_codec snd_hwdep mei_me snd_hda_core mei snd_pcm lpc_ich i915 r8169 mii prime_numbers [ 420.842357] CPU: 4 PID: 8714 Comm: kms_pipe_crc_ba Tainted: G U W 4.10.0-CI-CI_DRM_2280+ #1 [ 420.842377] Hardware name: Hewlett-Packard HP Pro 3500 Series/2ABF, BIOS 8.11 10/24/2012 [ 420.842395] task: ffff880117ddce40 task.stack: ffffc90001114000 [ 420.842439] RIP: 0010:__intel_engine_remove_wait+0x1f4/0x200 [i915] [ 420.842454] RSP: 0018:ffffc90001117b18 EFLAGS: 00010046 [ 420.842467] RAX: 0000000000000000 RBX: ffff88010c25c2a8 RCX: 0000000000000001 [ 420.842481] RDX: 0000000000000001 RSI: 00000000ffffffff RDI: ffffc90001117c50 [ 420.842495] RBP: ffffc90001117b58 R08: 0000000011e52352 R09: c4d16acc00000000 [ 420.842511] R10: ffffffff82789eb0 R11: ffff880117ddce40 R12: ffffc90001117c50 [ 420.842525] R13: ffffc90001117c50 R14: 0000000000000078 R15: 0000000000000000 [ 420.842540] FS: 00007fe47dda0a40(0000) GS:ffff88011fb00000(0000) knlGS:0000000000000000 [ 420.842559] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 420.842571] CR2: 00007fd6c0a2cec4 CR3: 000000010a5e5000 CR4: 00000000001406e0 [ 420.842586] Call Trace: [ 420.842595] ? do_raw_spin_lock+0xad/0xb0 [ 420.842635] intel_engine_remove_wait.part.3+0x26/0x40 [i915] [ 420.842678] intel_engine_remove_wait+0xe/0x20 [i915] [ 420.842721] i915_wait_request+0x4f0/0x8c0 [i915] [ 420.842736] ? wake_up_q+0x70/0x70 [ 420.842747] ? wake_up_q+0x70/0x70 [ 420.842787] i915_gem_object_wait_fence+0x7d/0x1a0 [i915] [ 420.842829] i915_gem_object_wait+0x30d/0x520 [i915] [ 420.842842] ? __this_cpu_preempt_check+0x13/0x20 [ 420.842884] i915_gem_wait_ioctl+0x12e/0x2e0 [i915] [ 420.842924] ? i915_gem_wait_ioctl+0x22/0x2e0 [i915] [ 420.842939] drm_ioctl+0x200/0x450 [ 420.842976] ? i915_gem_set_wedged+0x90/0x90 [i915] [ 420.842993] do_vfs_ioctl+0x90/0x6e0 [ 420.843003] ? entry_SYSCALL_64_fastpath+0x5/0xb1 [ 420.843017] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843030] ? trace_hardirqs_on_caller+0xe7/0x200 [ 420.843042] SyS_ioctl+0x3c/0x70 [ 420.843054] entry_SYSCALL_64_fastpath+0x1c/0xb1 [ 420.843065] RIP: 0033:0x7fe47c4b9357 [ 420.843075] RSP: 002b:00007ffc3c0633c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 420.843094] RAX: ffffffffffffffda RBX: ffffffff81482393 RCX: 00007fe47c4b9357 [ 420.843109] RDX: 00007ffc3c063400 RSI: 00000000c010646c RDI: 0000000000000004 [ 420.843123] RBP: ffffc90001117f88 R08: 0000000000000008 R09: 0000000000000000 [ 420.843137] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 [ 420.843151] R13: 0000000000000004 R14: 00000000c010646c R15: 0000000000000000 [ 420.843168] ? __this_cpu_preempt_check+0x13/0x20 [ 420.843180] Code: 81 48 c7 c1 40 6a 16 a0 48 c7 c2 47 29 15 a0 be 17 01 00 00 48 c7 c7 10 6a 16 a0 e8 c7 ea fe e0 e9 5d ff ff ff 0f 0b 0f 0b 0f 0b <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 e8 67 41 7e e1 [ 420.843325] RIP: __intel_engine_remove_wait+0x1f4/0x200 [i915] RSP: ffffc90001117b18 Fixes: b66255f0f779 ("drm/i915: Refactor wakeup of the next breadcrumb waiter") Fixes: 67b807a89230 ("drm/i915: Delay disabling the user interrupt for breadcrumbs") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170306092916.11623-2-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
2017-03-06 17:29:15 +08:00
missed_breadcrumb(engine);
}
b->waiters = RB_ROOT;
spin_unlock_irq(&b->rb_lock);
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
}
drm/i915: Only start with the fake-irq timer if interrupts are dead As a backup to waiting on a user-interrupt from the GPU, we use a heavy and frequent timer to wake up the waiting process should we detect an inconsistency whilst waiting. After seeing a "missed interrupt", the next time we wait, we restart the heavy timer. This patch is more reluctant to restart the timer and will only do so if we have not see any interrupts since when we started the fake irq timer. If we are seeing interrupts, then the waiters are being woken normally and we had an incoherency that caused to miss last time - that is unlikely to reoccur and so taking the risk of stalling again seems pragmatic. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170217151304.16665-5-chris@chris-wilson.co.uk
2017-02-17 23:13:03 +08:00
static bool use_fake_irq(const struct intel_breadcrumbs *b)
{
const struct intel_engine_cs *engine =
container_of(b, struct intel_engine_cs, breadcrumbs);
if (!test_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings))
return false;
/* Only start with the heavy weight fake irq timer if we have not
* seen any interrupts since enabling it the first time. If the
* interrupts are still arriving, it means we made a mistake in our
* engine->seqno_barrier(), a timing error that should be transient
* and unlikely to reoccur.
*/
return atomic_read(&engine->irq_count) == b->hangcheck_interrupts;
}
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
static void enable_fake_irq(struct intel_breadcrumbs *b)
{
/* Ensure we never sleep indefinitely */
if (!b->irq_enabled || use_fake_irq(b))
mod_timer(&b->fake_irq, jiffies + 1);
else
mod_timer(&b->hangcheck, wait_timeout());
}
drm/i915: Always double check for a missed interrupt for new bottom halves After assigning ourselves as the new bottom-half, we must perform a cursory check to prevent a missed interrupt. Either we miss the interrupt whilst programming the hardware, or if there was a previous waiter (for a later seqno) they may be woken instead of us (due to the inherent race in the unlocked read of b->tasklet in the irq handler) and so we miss the wake up. Spotted-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96806 Fixes: 688e6c725816 ("drm/i915: Slaughter the thundering... herd") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467805142-22219-1-git-send-email-chris@chris-wilson.co.uk
2016-07-06 19:39:00 +08:00
static void __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
{
struct intel_engine_cs *engine =
container_of(b, struct intel_engine_cs, breadcrumbs);
struct drm_i915_private *i915 = engine->i915;
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
lockdep_assert_held(&b->irq_lock);
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
if (b->irq_armed)
drm/i915: Always double check for a missed interrupt for new bottom halves After assigning ourselves as the new bottom-half, we must perform a cursory check to prevent a missed interrupt. Either we miss the interrupt whilst programming the hardware, or if there was a previous waiter (for a later seqno) they may be woken instead of us (due to the inherent race in the unlocked read of b->tasklet in the irq handler) and so we miss the wake up. Spotted-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96806 Fixes: 688e6c725816 ("drm/i915: Slaughter the thundering... herd") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467805142-22219-1-git-send-email-chris@chris-wilson.co.uk
2016-07-06 19:39:00 +08:00
return;
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
/* The breadcrumb irq will be disarmed on the interrupt after the
* waiters are signaled. This gives us a single interrupt window in
* which we can add a new waiter and avoid the cost of re-enabling
* the irq.
*/
b->irq_armed = true;
GEM_BUG_ON(b->irq_enabled);
drm/i915: Add unit tests for the breadcrumb rbtree, insert/remove First retroactive test, make sure that the waiters are in global seqno order after random inserts and removals. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170213171558.20942-3-chris@chris-wilson.co.uk
2017-02-14 01:15:14 +08:00
if (I915_SELFTEST_ONLY(b->mock)) {
/* For our mock objects we want to avoid interaction
* with the real hardware (which is not set up). So
* we simply pretend we have enabled the powerwell
* and the irq, and leave it up to the mock
* implementation to call intel_engine_wakeup()
* itself when it wants to simulate a user interrupt,
*/
return;
}
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
/* Since we are waiting on a request, the GPU should be busy
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
* and should have its own rpm reference. This is tracked
* by i915->gt.awake, we can forgo holding our own wakref
* for the interrupt as before i915->gt.awake is released (when
* the driver is idle) we disarm the breadcrumbs.
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
*/
/* No interrupts? Kick the waiter every jiffie! */
if (intel_irqs_enabled(i915)) {
drm/i915: Only apply one barrier after a breadcrumb interrupt is posted If we flag the seqno as potentially stale upon receiving an interrupt, we can use that information to reduce the frequency that we apply the heavyweight coherent seqno read (i.e. if we wake up a chain of waiters). v2: Use cmpxchg to replace READ_ONCE/WRITE_ONCE for more explicit control of the ordering wrt to interrupt generation and interrupt checking in the bottom-half. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-14-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:23 +08:00
if (!test_bit(engine->id, &i915->gpu_error.test_irq_rings))
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
irq_enable(engine);
b->irq_enabled = true;
}
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
enable_fake_irq(b);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
}
static inline struct intel_wait *to_wait(struct rb_node *node)
{
drm/i915/breadcrumbs: s/container_of/rb_entry/ In keeping with commit f802cf7e0986 ("drm/i915/debugfs: use rb_entry()"), convert the primary user of the rbtrees over to using rb_entry rather than the equivalent container_of. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/20161220104003.8044-1-chris@chris-wilson.co.uk Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2016-12-20 18:40:03 +08:00
return rb_entry(node, struct intel_wait, node);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
}
static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
struct intel_wait *wait)
{
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
lockdep_assert_held(&b->rb_lock);
drm/i915/breadcrumbs: Assert that we do not shortcut the current bottom-half We need to ensure that we always serialize updates to the bottom-half using the breadcrumbs.irq_lock so that we don't race with a concurrent interrupt handler. This is most important just prior to leaving the waiter (when the intel_wait will be overwritten), so make sure we are not the current bottom-half when skipping the irq locks. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-4-chris@chris-wilson.co.uk
2017-03-16 05:07:25 +08:00
GEM_BUG_ON(b->irq_wait == wait);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
/* This request is completed, so remove it from the tree, mark it as
drm/i915/breadcrumbs: Tweak commentary Tvrtko spotted a stale reference to b->lock (now b->rb_lock) so review the comments and try to improve them in passing. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315222259.1469-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-03-16 06:22:59 +08:00
* complete, and *then* wake up the associated task. N.B. when the
* task wakes up, it will find the empty rb_node, discern that it
* has already been removed from the tree and skip the serialisation
* of the b->rb_lock and b->irq_lock. This means that the destruction
* of the intel_wait is not serialised with the interrupt handler
* by the waiter - it must instead be serialised by the caller.
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
*/
rb_erase(&wait->node, &b->waiters);
RB_CLEAR_NODE(&wait->node);
wake_up_process(wait->tsk); /* implicit smp_wmb() */
}
drm/i915: Refactor wakeup of the next breadcrumb waiter Refactor the common task of updating the first_waiter, serialised with the interrupt handler. When we update the first_waiter, we also need to wakeup the new bottom-half in order to complete the actions that we may have delegated to it (such as checking the irq-seqno coherency or waking up other lower priority concurrent waiters). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303171422.4735-1-chris@chris-wilson.co.uk
2017-03-04 01:14:22 +08:00
static inline void __intel_breadcrumbs_next(struct intel_engine_cs *engine,
struct rb_node *next)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock(&b->irq_lock);
drm/i915: Refactor wakeup of the next breadcrumb waiter Refactor the common task of updating the first_waiter, serialised with the interrupt handler. When we update the first_waiter, we also need to wakeup the new bottom-half in order to complete the actions that we may have delegated to it (such as checking the irq-seqno coherency or waking up other lower priority concurrent waiters). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303171422.4735-1-chris@chris-wilson.co.uk
2017-03-04 01:14:22 +08:00
GEM_BUG_ON(!b->irq_armed);
drm/i915/breadcrumbs: Update bottom-half before marking as complete When adding a new request to the breadcrumb rbtree, we mark all those requests inside the rbtree that are already completed as complete. This wakes those waiters up and allows them to skip the spinlock before returning to userspace. If one of those is the current bottom-half and allocated its intel_wait on the stack, it may then overwrite the b->irq_wait upon exiting i915_wait_request() just as the interrupt handler dereferences it. Fixes: 56299fb7d904 ("drm/i915: Signal first fence from irq handler if complete") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-2-chris@chris-wilson.co.uk
2017-03-16 05:07:23 +08:00
GEM_BUG_ON(!b->irq_wait);
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
b->irq_wait = to_wait(next);
spin_unlock(&b->irq_lock);
drm/i915: Refactor wakeup of the next breadcrumb waiter Refactor the common task of updating the first_waiter, serialised with the interrupt handler. When we update the first_waiter, we also need to wakeup the new bottom-half in order to complete the actions that we may have delegated to it (such as checking the irq-seqno coherency or waking up other lower priority concurrent waiters). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303171422.4735-1-chris@chris-wilson.co.uk
2017-03-04 01:14:22 +08:00
/* We always wake up the next waiter that takes over as the bottom-half
* as we may delegate not only the irq-seqno barrier to the next waiter
* but also the task of waking up concurrent waiters.
*/
if (next)
wake_up_process(to_wait(next)->tsk);
}
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
struct intel_wait *wait)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
struct rb_node **p, *parent, *completed;
bool first;
u32 seqno;
/* Insert the request into the retirement ordered list
* of waiters by walking the rbtree. If we are the oldest
* seqno in the tree (the first to be retired), then
* set ourselves as the bottom-half.
*
* As we descend the tree, prune completed branches since we hold the
* spinlock we know that the first_waiter must be delayed and can
* reduce some of the sequential wake up latency if we take action
* ourselves and wake up the completed tasks in parallel. Also, by
* removing stale elements in the tree, we may be able to reduce the
* ping-pong between the old bottom-half and ourselves as first-waiter.
*/
first = true;
parent = NULL;
completed = NULL;
drm/i915: Use HWS for seqno tracking everywhere By using the same address for storing the HWS on every platform, we can remove the platform specific vfuncs and reduce the get-seqno routine to a single read of a cached memory location. v2: Fix semaphore_passed() to look at the signaling engine (not the waiter's) Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-8-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:17 +08:00
seqno = intel_engine_get_seqno(engine);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
/* If the request completed before we managed to grab the spinlock,
* return now before adding ourselves to the rbtree. We let the
* current bottom-half handle any pending wakeups and instead
* try and get out of the way quickly.
*/
if (i915_seqno_passed(seqno, wait->seqno)) {
RB_CLEAR_NODE(&wait->node);
return first;
}
p = &b->waiters.rb_node;
while (*p) {
parent = *p;
if (wait->seqno == to_wait(parent)->seqno) {
/* We have multiple waiters on the same seqno, select
* the highest priority task (that with the smallest
* task->prio) to serve as the bottom-half for this
* group.
*/
if (wait->tsk->prio > to_wait(parent)->tsk->prio) {
p = &parent->rb_right;
first = false;
} else {
p = &parent->rb_left;
}
} else if (i915_seqno_passed(wait->seqno,
to_wait(parent)->seqno)) {
p = &parent->rb_right;
if (i915_seqno_passed(seqno, to_wait(parent)->seqno))
completed = parent;
else
first = false;
} else {
p = &parent->rb_left;
}
}
rb_link_node(&wait->node, parent, p);
rb_insert_color(&wait->node, &b->waiters);
if (first) {
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock(&b->irq_lock);
b->irq_wait = wait;
drm/i915: Always double check for a missed interrupt for new bottom halves After assigning ourselves as the new bottom-half, we must perform a cursory check to prevent a missed interrupt. Either we miss the interrupt whilst programming the hardware, or if there was a previous waiter (for a later seqno) they may be woken instead of us (due to the inherent race in the unlocked read of b->tasklet in the irq handler) and so we miss the wake up. Spotted-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96806 Fixes: 688e6c725816 ("drm/i915: Slaughter the thundering... herd") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467805142-22219-1-git-send-email-chris@chris-wilson.co.uk
2016-07-06 19:39:00 +08:00
/* After assigning ourselves as the new bottom-half, we must
* perform a cursory check to prevent a missed interrupt.
* Either we miss the interrupt whilst programming the hardware,
* or if there was a previous waiter (for a later seqno) they
* may be woken instead of us (due to the inherent race
drm/i915: Group the irq breadcrumb variables into the same cacheline As we inspect both the tasklet (to check for an active bottom-half) and set the irq-posted flag at the same time (both in the interrupt handler and then in the bottom-halt), group those two together into the same cacheline. (Not having total control over placement of the struct means we can't guarantee the cacheline boundary, we need to align the kmalloc and then each struct, but the grouping should help.) v2: Try a couple of different names for the state touched by the user interrupt handler. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467805142-22219-3-git-send-email-chris@chris-wilson.co.uk
2016-07-06 19:39:02 +08:00
* in the unlocked read of b->irq_seqno_bh in the irq handler)
* and so we miss the wake up.
drm/i915: Always double check for a missed interrupt for new bottom halves After assigning ourselves as the new bottom-half, we must perform a cursory check to prevent a missed interrupt. Either we miss the interrupt whilst programming the hardware, or if there was a previous waiter (for a later seqno) they may be woken instead of us (due to the inherent race in the unlocked read of b->tasklet in the irq handler) and so we miss the wake up. Spotted-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96806 Fixes: 688e6c725816 ("drm/i915: Slaughter the thundering... herd") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467805142-22219-1-git-send-email-chris@chris-wilson.co.uk
2016-07-06 19:39:00 +08:00
*/
__intel_breadcrumbs_enable_irq(b);
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_unlock(&b->irq_lock);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
}
drm/i915/breadcrumbs: Update bottom-half before marking as complete When adding a new request to the breadcrumb rbtree, we mark all those requests inside the rbtree that are already completed as complete. This wakes those waiters up and allows them to skip the spinlock before returning to userspace. If one of those is the current bottom-half and allocated its intel_wait on the stack, it may then overwrite the b->irq_wait upon exiting i915_wait_request() just as the interrupt handler dereferences it. Fixes: 56299fb7d904 ("drm/i915: Signal first fence from irq handler if complete") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-2-chris@chris-wilson.co.uk
2017-03-16 05:07:23 +08:00
if (completed) {
drm/i915/breadcrumbs: Tweak commentary Tvrtko spotted a stale reference to b->lock (now b->rb_lock) so review the comments and try to improve them in passing. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315222259.1469-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-03-16 06:22:59 +08:00
/* Advance the bottom-half (b->irq_wait) before we wake up
* the waiters who may scribble over their intel_wait
* just as the interrupt handler is dereferencing it via
* b->irq_wait.
*/
drm/i915/breadcrumbs: Update bottom-half before marking as complete When adding a new request to the breadcrumb rbtree, we mark all those requests inside the rbtree that are already completed as complete. This wakes those waiters up and allows them to skip the spinlock before returning to userspace. If one of those is the current bottom-half and allocated its intel_wait on the stack, it may then overwrite the b->irq_wait upon exiting i915_wait_request() just as the interrupt handler dereferences it. Fixes: 56299fb7d904 ("drm/i915: Signal first fence from irq handler if complete") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-2-chris@chris-wilson.co.uk
2017-03-16 05:07:23 +08:00
if (!first) {
struct rb_node *next = rb_next(completed);
GEM_BUG_ON(next == &wait->node);
__intel_breadcrumbs_next(engine, next);
}
do {
struct intel_wait *crumb = to_wait(completed);
completed = rb_prev(completed);
__intel_breadcrumbs_finish(b, crumb);
} while (completed);
}
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
GEM_BUG_ON(!b->irq_wait);
drm/i915/breadcrumbs: Update bottom-half before marking as complete When adding a new request to the breadcrumb rbtree, we mark all those requests inside the rbtree that are already completed as complete. This wakes those waiters up and allows them to skip the spinlock before returning to userspace. If one of those is the current bottom-half and allocated its intel_wait on the stack, it may then overwrite the b->irq_wait upon exiting i915_wait_request() just as the interrupt handler dereferences it. Fixes: 56299fb7d904 ("drm/i915: Signal first fence from irq handler if complete") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-2-chris@chris-wilson.co.uk
2017-03-16 05:07:23 +08:00
GEM_BUG_ON(!b->irq_armed);
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
GEM_BUG_ON(rb_first(&b->waiters) != &b->irq_wait->node);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
return first;
}
bool intel_engine_add_wait(struct intel_engine_cs *engine,
struct intel_wait *wait)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
bool first;
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock_irq(&b->rb_lock);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
first = __intel_engine_add_wait(engine, wait);
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_unlock_irq(&b->rb_lock);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
return first;
}
static inline bool chain_wakeup(struct rb_node *rb, int priority)
{
return rb && to_wait(rb)->tsk->prio <= priority;
}
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
static inline int wakeup_priority(struct intel_breadcrumbs *b,
struct task_struct *tsk)
{
if (tsk == b->signaler)
return INT_MIN;
else
return tsk->prio;
}
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
static void __intel_engine_remove_wait(struct intel_engine_cs *engine,
struct intel_wait *wait)
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
lockdep_assert_held(&b->rb_lock);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
if (RB_EMPTY_NODE(&wait->node))
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
goto out;
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
if (b->irq_wait == wait) {
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
const int priority = wakeup_priority(b, wait->tsk);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
struct rb_node *next;
/* We are the current bottom-half. Find the next candidate,
* the first waiter in the queue on the remaining oldest
* request. As multiple seqnos may complete in the time it
* takes us to wake up and find the next waiter, we have to
* wake up that waiter for it to perform its own coherent
* completion check.
*/
next = rb_next(&wait->node);
if (chain_wakeup(next, priority)) {
/* If the next waiter is already complete,
* wake it up and continue onto the next waiter. So
* if have a small herd, they will wake up in parallel
* rather than sequentially, which should reduce
* the overall latency in waking all the completed
* clients.
*
* However, waking up a chain adds extra latency to
* the first_waiter. This is undesirable if that
* waiter is a high priority task.
*/
drm/i915: Use HWS for seqno tracking everywhere By using the same address for storing the HWS on every platform, we can remove the platform specific vfuncs and reduce the get-seqno routine to a single read of a cached memory location. v2: Fix semaphore_passed() to look at the signaling engine (not the waiter's) Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-8-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:17 +08:00
u32 seqno = intel_engine_get_seqno(engine);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
while (i915_seqno_passed(seqno, to_wait(next)->seqno)) {
struct rb_node *n = rb_next(next);
__intel_breadcrumbs_finish(b, to_wait(next));
next = n;
if (!chain_wakeup(next, priority))
break;
}
}
drm/i915: Refactor wakeup of the next breadcrumb waiter Refactor the common task of updating the first_waiter, serialised with the interrupt handler. When we update the first_waiter, we also need to wakeup the new bottom-half in order to complete the actions that we may have delegated to it (such as checking the irq-seqno coherency or waking up other lower priority concurrent waiters). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303171422.4735-1-chris@chris-wilson.co.uk
2017-03-04 01:14:22 +08:00
__intel_breadcrumbs_next(engine, next);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
} else {
GEM_BUG_ON(rb_first(&b->waiters) == &wait->node);
}
GEM_BUG_ON(RB_EMPTY_NODE(&wait->node));
rb_erase(&wait->node, &b->waiters);
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
out:
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
GEM_BUG_ON(b->irq_wait == wait);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
GEM_BUG_ON(rb_first(&b->waiters) !=
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
(b->irq_wait ? &b->irq_wait->node : NULL));
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
}
void intel_engine_remove_wait(struct intel_engine_cs *engine,
struct intel_wait *wait)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
/* Quick check to see if this waiter was already decoupled from
* the tree by the bottom-half to avoid contention on the spinlock
* by the herd.
*/
drm/i915/breadcrumbs: Assert that we do not shortcut the current bottom-half We need to ensure that we always serialize updates to the bottom-half using the breadcrumbs.irq_lock so that we don't race with a concurrent interrupt handler. This is most important just prior to leaving the waiter (when the intel_wait will be overwritten), so make sure we are not the current bottom-half when skipping the irq locks. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-4-chris@chris-wilson.co.uk
2017-03-16 05:07:25 +08:00
if (RB_EMPTY_NODE(&wait->node)) {
GEM_BUG_ON(READ_ONCE(b->irq_wait) == wait);
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
return;
drm/i915/breadcrumbs: Assert that we do not shortcut the current bottom-half We need to ensure that we always serialize updates to the bottom-half using the breadcrumbs.irq_lock so that we don't race with a concurrent interrupt handler. This is most important just prior to leaving the waiter (when the intel_wait will be overwritten), so make sure we are not the current bottom-half when skipping the irq locks. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-4-chris@chris-wilson.co.uk
2017-03-16 05:07:25 +08:00
}
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock_irq(&b->rb_lock);
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
__intel_engine_remove_wait(engine, wait);
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_unlock_irq(&b->rb_lock);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
}
drm/i915: Remove the preempted request from the execution queue After the request is cancelled, we then need to remove it from the global execution timeline and return it to the context timeline, the inverse of submit_request(). v2: Move manipulation of struct intel_wait to helpers Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-12-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-02-23 15:44:17 +08:00
static bool signal_valid(const struct drm_i915_gem_request *request)
{
return intel_wait_check_request(&request->signaling.wait, request);
}
static bool signal_complete(const struct drm_i915_gem_request *request)
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
{
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
if (!request)
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
return false;
/* If another process served as the bottom-half it may have already
* signalled that this wait is already completed.
*/
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
if (intel_wait_complete(&request->signaling.wait))
drm/i915: Remove the preempted request from the execution queue After the request is cancelled, we then need to remove it from the global execution timeline and return it to the context timeline, the inverse of submit_request(). v2: Move manipulation of struct intel_wait to helpers Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-12-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-02-23 15:44:17 +08:00
return signal_valid(request);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
/* Carefully check if the request is complete, giving time for the
* seqno to be visible or if the GPU hung.
*/
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
if (__i915_request_irq_complete(request))
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
return true;
return false;
}
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
static struct drm_i915_gem_request *to_signaler(struct rb_node *rb)
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
{
drm/i915/breadcrumbs: s/container_of/rb_entry/ In keeping with commit f802cf7e0986 ("drm/i915/debugfs: use rb_entry()"), convert the primary user of the rbtrees over to using rb_entry rather than the equivalent container_of. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/20161220104003.8044-1-chris@chris-wilson.co.uk Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2016-12-20 18:40:03 +08:00
return rb_entry(rb, struct drm_i915_gem_request, signaling.node);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
}
static void signaler_set_rtpriority(void)
{
struct sched_param param = { .sched_priority = 1 };
sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
}
static int intel_breadcrumbs_signaler(void *arg)
{
struct intel_engine_cs *engine = arg;
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
struct drm_i915_gem_request *request;
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
/* Install ourselves with high priority to reduce signalling latency */
signaler_set_rtpriority();
do {
drm/i915: Apply a cond_resched() to the saturated signaler If the engine is continually completing nops, we can saturate the signaler and keep it working indefinitely. This angers the NMI watchdog! A good example is to disable semaphores on snb and run igt/gem_exec_nop - the parallel, multi-engine workloads are more than sufficient to hog the CPU, preventing the system from even processing ICMP echo replies. v2: Tvrtko dug into cond_resched() on x86 and found that it only depended upon preempt_count and not tif_need_resched() - which means that we would always call schedule() at that point. Fixes: c81d46138da6 ("drm/i915: Convert trace-irq to the breadcrumb waiter") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170404120531.10737-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-04-04 20:05:31 +08:00
bool do_schedule = true;
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
set_current_state(TASK_INTERRUPTIBLE);
/* We are either woken up by the interrupt bottom-half,
* or by a client adding a new signaller. In both cases,
* the GPU seqno may have advanced beyond our oldest signal.
* If it has, propagate the signal, remove the waiter and
* check again with the next oldest signal. Otherwise we
* need to wait for a new interrupt from the GPU or for
* a new client.
*/
drm/i915: Take a reference whilst processing the signaler request The plan in the near-future is to allow requests to be removed from the signaler. We can no longer then rely on holding a reference to the request for the duration it is in the signaling tree, and instead must obtain a reference to the request for the current operation using RCU. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
2017-02-23 15:44:15 +08:00
rcu_read_lock();
request = rcu_dereference(b->first_signal);
if (request)
request = i915_gem_request_get_rcu(request);
rcu_read_unlock();
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
if (signal_complete(request)) {
drm/i915: Emit dma-fence (and execlists submit) first from signaler When introduced, I thought that reducing client latency from the signaler was the priority. Since its inception the signaler has become responsible for keeping the execlists full, via the dma-fence. As this is very important to minimise overall execution time, signal the dma-fence first and then signal any waiting clients. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170124110009.28947-8-chris@chris-wilson.co.uk
2017-01-24 19:00:09 +08:00
local_bh_disable();
dma_fence_signal(&request->fence);
local_bh_enable(); /* kick start the tasklets */
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock_irq(&b->rb_lock);
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
/* Wake up all other completed waiters and select the
* next bottom-half for the next user interrupt.
*/
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
__intel_engine_remove_wait(engine,
&request->signaling.wait);
drm/i915: Drive request submission through fence callbacks Drive final request submission from a callback from the fence. This way the request is queued until all dependencies are resolved, at which point it is handed to the backend for queueing to hardware. At this point, no dependencies are set on the request, so the callback is immediate. A side-effect of imposing a heavier-irqsafe spinlock for execlist submission is that we lose the softirq enabling after scheduling the execlists tasklet. To compensate, we manually kickstart the softirq by disabling and enabling the bh around the fence signaling. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: John Harrison <john.c.harrison@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20160909131201.16673-14-chris@chris-wilson.co.uk
2016-09-09 21:11:54 +08:00
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
/* Find the next oldest signal. Note that as we have
* not been holding the lock, another client may
* have installed an even older signal than the one
* we just completed - so double check we are still
* the oldest before picking the next one.
*/
drm/i915: Take a reference whilst processing the signaler request The plan in the near-future is to allow requests to be removed from the signaler. We can no longer then rely on holding a reference to the request for the duration it is in the signaling tree, and instead must obtain a reference to the request for the current operation using RCU. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
2017-02-23 15:44:15 +08:00
if (request == rcu_access_pointer(b->first_signal)) {
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
struct rb_node *rb =
rb_next(&request->signaling.node);
drm/i915: Take a reference whilst processing the signaler request The plan in the near-future is to allow requests to be removed from the signaler. We can no longer then rely on holding a reference to the request for the duration it is in the signaling tree, and instead must obtain a reference to the request for the current operation using RCU. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
2017-02-23 15:44:15 +08:00
rcu_assign_pointer(b->first_signal,
rb ? to_signaler(rb) : NULL);
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
}
rb_erase(&request->signaling.node, &b->signals);
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
RB_CLEAR_NODE(&request->signaling.node);
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_unlock_irq(&b->rb_lock);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
drm/i915: Rename request reference/unreference to get/put Now that we derive requests from struct fence, swap over to its nomenclature for references. It's shorter and more idiomatic across the kernel. s/i915_gem_request_reference/i915_gem_request_get/ s/i915_gem_request_unreference/i915_gem_request_put/ Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: http://patchwork.freedesktop.org/patch/msgid/1469005202-9659-2-git-send-email-chris@chris-wilson.co.uk Link: http://patchwork.freedesktop.org/patch/msgid/1469017917-15134-1-git-send-email-chris@chris-wilson.co.uk
2016-07-20 20:31:49 +08:00
i915_gem_request_put(request);
drm/i915: Apply a cond_resched() to the saturated signaler If the engine is continually completing nops, we can saturate the signaler and keep it working indefinitely. This angers the NMI watchdog! A good example is to disable semaphores on snb and run igt/gem_exec_nop - the parallel, multi-engine workloads are more than sufficient to hog the CPU, preventing the system from even processing ICMP echo replies. v2: Tvrtko dug into cond_resched() on x86 and found that it only depended upon preempt_count and not tif_need_resched() - which means that we would always call schedule() at that point. Fixes: c81d46138da6 ("drm/i915: Convert trace-irq to the breadcrumb waiter") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170404120531.10737-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-04-04 20:05:31 +08:00
/* If the engine is saturated we may be continually
* processing completed requests. This angers the
* NMI watchdog if we never let anything else
* have access to the CPU. Let's pretend to be nice
* and relinquish the CPU if we burn through the
* entire RT timeslice!
*/
do_schedule = need_resched();
}
if (unlikely(do_schedule)) {
drm/i915: Remove the preempted request from the execution queue After the request is cancelled, we then need to remove it from the global execution timeline and return it to the context timeline, the inverse of submit_request(). v2: Move manipulation of struct intel_wait to helpers Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-12-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-02-23 15:44:17 +08:00
DEFINE_WAIT(exec);
drm/i915: Park the signaler before sleeping If the signal to park arrives before we sleep, then we need to check kthread_should_park() before sleeping to avoid missing the signal. Otherwise, if the signal arrives whilst we are processing completed requests, we will reset the current->state back to TASK_INTERRUPTIBLE and so miss the wakeup. Fixes: fe3288b5da2c ("drm/i915: Park the breadcrumbs signaler across a GPU reset") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170403105124.8969-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-04-03 18:51:24 +08:00
if (kthread_should_park())
kthread_parkme();
drm/i915: Take a reference whilst processing the signaler request The plan in the near-future is to allow requests to be removed from the signaler. We can no longer then rely on holding a reference to the request for the duration it is in the signaling tree, and instead must obtain a reference to the request for the current operation using RCU. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
2017-02-23 15:44:15 +08:00
if (kthread_should_stop()) {
GEM_BUG_ON(request);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
break;
drm/i915: Take a reference whilst processing the signaler request The plan in the near-future is to allow requests to be removed from the signaler. We can no longer then rely on holding a reference to the request for the duration it is in the signaling tree, and instead must obtain a reference to the request for the current operation using RCU. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
2017-02-23 15:44:15 +08:00
}
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
drm/i915: Remove the preempted request from the execution queue After the request is cancelled, we then need to remove it from the global execution timeline and return it to the context timeline, the inverse of submit_request(). v2: Move manipulation of struct intel_wait to helpers Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-12-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-02-23 15:44:17 +08:00
if (request)
add_wait_queue(&request->execute, &exec);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
schedule();
drm/i915: Park the breadcrumbs signaler across a GPU reset The signal threads may be running concurrently with the GPU reset. The completion from the GPU run asynchronous with the reset and two threads may see different snapshots of the state, and the signaler may mark a request as complete as we try to reset it. We don't tolerate 2 different views of the same state and complain if we try to mark a request as failed if it is already complete. Disable the signal threads during reset to prevent this conflict (even though the conflict implies that the state we resetting to is invalid, we have already made our decision!). Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99733 References: https://bugs.freedesktop.org/show_bug.cgi?id=99671 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170212172002.23072-4-chris@chris-wilson.co.uk Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
2017-02-13 01:20:01 +08:00
drm/i915: Remove the preempted request from the execution queue After the request is cancelled, we then need to remove it from the global execution timeline and return it to the context timeline, the inverse of submit_request(). v2: Move manipulation of struct intel_wait to helpers Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-12-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-02-23 15:44:17 +08:00
if (request)
remove_wait_queue(&request->execute, &exec);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
}
drm/i915: Take a reference whilst processing the signaler request The plan in the near-future is to allow requests to be removed from the signaler. We can no longer then rely on holding a reference to the request for the duration it is in the signaling tree, and instead must obtain a reference to the request for the current operation using RCU. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
2017-02-23 15:44:15 +08:00
i915_gem_request_put(request);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
} while (1);
__set_current_state(TASK_RUNNING);
return 0;
}
drm/i915: Skip waking the signaler when enabling before request submission If we are enabling the breadcrumbs signaling prior to submitting the request, we know that we cannot have missed the interrupt and can therefore skip immediately waking the signaler to check. This reduces a significant chunk of the __i915_gem_request_submit() overhead for inter-engine synchronisation, for example in gem_exec_whisper. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170426080659.28771-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-04-26 16:06:59 +08:00
void intel_engine_enable_signaling(struct drm_i915_gem_request *request,
bool wakeup)
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
{
struct intel_engine_cs *engine = request->engine;
struct intel_breadcrumbs *b = &engine->breadcrumbs;
struct rb_node *parent, **p;
drm/i915: Skip waking the signaler when enabling before request submission If we are enabling the breadcrumbs signaling prior to submitting the request, we know that we cannot have missed the interrupt and can therefore skip immediately waking the signaler to check. This reduces a significant chunk of the __i915_gem_request_submit() overhead for inter-engine synchronisation, for example in gem_exec_whisper. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170426080659.28771-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-04-26 16:06:59 +08:00
bool first;
drm/i915: Protect the request->global_seqno with the engine->timeline lock A request is assigned a global seqno only when it is on the hardware execution queue. The global seqno can be used to maintain a list of requests on the same engine in retirement order, for example for constructing a priority queue for waiting. Prior to its execution, or if it is subsequently removed in the event of preemption, its global seqno is zero. As both insertion and removal from the execution queue may operate in IRQ context, it is not guarded by the usual struct_mutex BKL. Instead those relying on the global seqno must be prepared for its value to change between reads. Only when the request is complete can the global seqno be stable (due to the memory barriers on submitting the commands to the hardware to write the breadcrumb, if the HWS shows that it has passed the global seqno and the global seqno is unchanged after the read, it is indeed complete). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-9-chris@chris-wilson.co.uk
2017-02-23 15:44:14 +08:00
u32 seqno;
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
drm/i915: Convert breadcrumbs spinlock to be irqsafe The breadcrumbs are about to be used from within IRQ context sections (e.g. nouveau signals a fence from an interrupt handler causing us to submit a new request) and/or from bottom-half tasklets (i.e. intel_lrc_irq_handler), therefore we need to employ the irqsafe spinlock variants. For example, deferring the request submission to the intel_lrc_irq_handler generates this trace: [ 66.388639] ================================= [ 66.388650] [ INFO: inconsistent lock state ] [ 66.388663] 4.9.0-rc2+ #56 Not tainted [ 66.388672] --------------------------------- [ 66.388682] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. [ 66.388695] swapper/1/0 [HC0[0]:SC1[1]:HE0:SE0] takes: [ 66.388706] (&(&b->lock)->rlock){+.?...} , at: [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.388761] {SOFTIRQ-ON-W} state was registered at: [ 66.388772] [ 66.388783] [<ffffffff810bd842>] __lock_acquire+0x682/0x1870 [ 66.388795] [ 66.388803] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.388814] [ 66.388824] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.388835] [ 66.388845] [<ffffffff81401e41>] intel_engine_reset_breadcrumbs+0x21/0xb0 [ 66.388857] [ 66.388866] [<ffffffff81403ae7>] gen8_init_common_ring+0x67/0x100 [ 66.388878] [ 66.388887] [<ffffffff81403b92>] gen8_init_render_ring+0x12/0x60 [ 66.388903] [ 66.388912] [<ffffffff813f8707>] i915_gem_init_hw+0xf7/0x2a0 [ 66.388927] [ 66.388936] [<ffffffff813f899b>] i915_gem_init+0xbb/0xf0 [ 66.388950] [ 66.388959] [<ffffffff813b4980>] i915_driver_load+0x7e0/0x1330 [ 66.388978] [ 66.388988] [<ffffffff813c09d8>] i915_pci_probe+0x28/0x40 [ 66.389003] [ 66.389013] [<ffffffff812fa0db>] pci_device_probe+0x8b/0xf0 [ 66.389028] [ 66.389037] [<ffffffff8147737e>] driver_probe_device+0x21e/0x430 [ 66.389056] [ 66.389065] [<ffffffff8147766e>] __driver_attach+0xde/0xe0 [ 66.389080] [ 66.389090] [<ffffffff814751ad>] bus_for_each_dev+0x5d/0x90 [ 66.389105] [ 66.389113] [<ffffffff81477799>] driver_attach+0x19/0x20 [ 66.389134] [ 66.389144] [<ffffffff81475ced>] bus_add_driver+0x15d/0x260 [ 66.389159] [ 66.389168] [<ffffffff81477e3b>] driver_register+0x5b/0xd0 [ 66.389183] [ 66.389281] [<ffffffff812fa19b>] __pci_register_driver+0x5b/0x60 [ 66.389301] [ 66.389312] [<ffffffff81aed333>] i915_init+0x3e/0x45 [ 66.389326] [ 66.389336] [<ffffffff81ac2ffa>] do_one_initcall+0x8b/0x118 [ 66.389350] [ 66.389359] [<ffffffff81ac323a>] kernel_init_freeable+0x1b3/0x23b [ 66.389378] [ 66.389387] [<ffffffff8160fc39>] kernel_init+0x9/0x100 [ 66.389402] [ 66.389411] [<ffffffff816180e7>] ret_from_fork+0x27/0x40 [ 66.389426] irq event stamp: 315865 [ 66.389438] hardirqs last enabled at (315864): [<ffffffff816178f1>] _raw_spin_unlock_irqrestore+0x31/0x50 [ 66.389469] hardirqs last disabled at (315865): [<ffffffff816176b3>] _raw_spin_lock_irqsave+0x13/0x50 [ 66.389499] softirqs last enabled at (315818): [<ffffffff8107a04c>] _local_bh_enable+0x1c/0x50 [ 66.389530] softirqs last disabled at (315819): [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.389559] [ 66.389559] other info that might help us debug this: [ 66.389580] Possible unsafe locking scenario: [ 66.389580] [ 66.389598] CPU0 [ 66.389609] ---- [ 66.389620] lock(&(&b->lock)->rlock); [ 66.389650] <Interrupt> [ 66.389661] lock(&(&b->lock)->rlock); [ 66.389690] [ 66.389690] *** DEADLOCK *** [ 66.389690] [ 66.389715] 2 locks held by swapper/1/0: [ 66.389728] #0: (&(&tl->lock)->rlock){..-...}, at: [<ffffffff81403e01>] intel_lrc_irq_handler+0x201/0x3c0 [ 66.389785] #1: (&(&req->lock)->rlock/1){..-...}, at: [<ffffffff813fc0af>] __i915_gem_request_submit+0x8f/0x170 [ 66.389854] [ 66.389854] stack backtrace: [ 66.389959] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.0-rc2+ #56 [ 66.389976] Hardware name: / , BIOS PYBSWCEL.86A.0027.2015.0507.1758 05/07/2015 [ 66.389999] ffff88027fd03c58 ffffffff812beae5 ffff88027696e680 ffffffff822afe20 [ 66.390036] ffff88027fd03ca8 ffffffff810bb420 0000000000000001 0000000000000000 [ 66.390070] 0000000000000000 0000000000000006 0000000000000004 ffff88027696ee10 [ 66.390104] Call Trace: [ 66.390117] <IRQ> [ 66.390128] [<ffffffff812beae5>] dump_stack+0x68/0x93 [ 66.390147] [<ffffffff810bb420>] print_usage_bug+0x1d0/0x1e0 [ 66.390164] [<ffffffff810bb8a0>] mark_lock+0x470/0x4f0 [ 66.390181] [<ffffffff810ba9d0>] ? print_shortest_lock_dependencies+0x1b0/0x1b0 [ 66.390203] [<ffffffff810bd75d>] __lock_acquire+0x59d/0x1870 [ 66.390221] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.390237] [<ffffffff810bedbc>] ? lock_acquire+0x6c/0xb0 [ 66.390255] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390273] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.390291] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390309] [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.390327] [<ffffffff813fc170>] __i915_gem_request_submit+0x150/0x170 [ 66.390345] [<ffffffff81403e8b>] intel_lrc_irq_handler+0x28b/0x3c0 [ 66.390363] [<ffffffff81079d97>] tasklet_action+0x57/0xc0 [ 66.390380] [<ffffffff8107a249>] __do_softirq+0x119/0x240 [ 66.390396] [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.390414] [<ffffffff8101afd5>] do_IRQ+0x65/0x110 [ 66.390431] [<ffffffff81618806>] common_interrupt+0x86/0x86 [ 66.390446] <EOI> [ 66.390457] [<ffffffff814ec6d1>] ? cpuidle_enter_state+0x151/0x200 [ 66.390480] [<ffffffff814ec7a2>] cpuidle_enter+0x12/0x20 [ 66.390498] [<ffffffff810b639e>] call_cpuidle+0x1e/0x40 [ 66.390516] [<ffffffff810b65ae>] cpu_startup_entry+0x10e/0x1f0 [ 66.390534] [<ffffffff81036133>] start_secondary+0x103/0x130 (This is split out of the defer global seqno allocation patch due to realisation that we need a more complete conversion if we want to defer request submission even further.) v2: lockdep was warning about mixed SOFTIRQ contexts not HARDIRQ contexts so we only need to use spin_lock_bh and not disable interrupts. v3: We need full irq protection as we may be called from a third party interrupt handler (via fences). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161028125858.23563-32-chris@chris-wilson.co.uk
2016-10-28 20:58:55 +08:00
/* Note that we may be called from an interrupt handler on another
* device (e.g. nouveau signaling a fence completion causing us
* to submit a request, and so enable signaling). As such,
drm/i915/breadcrumbs: Tweak commentary Tvrtko spotted a stale reference to b->lock (now b->rb_lock) so review the comments and try to improve them in passing. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315222259.1469-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-03-16 06:22:59 +08:00
* we need to make sure that all other users of b->rb_lock protect
drm/i915: Convert breadcrumbs spinlock to be irqsafe The breadcrumbs are about to be used from within IRQ context sections (e.g. nouveau signals a fence from an interrupt handler causing us to submit a new request) and/or from bottom-half tasklets (i.e. intel_lrc_irq_handler), therefore we need to employ the irqsafe spinlock variants. For example, deferring the request submission to the intel_lrc_irq_handler generates this trace: [ 66.388639] ================================= [ 66.388650] [ INFO: inconsistent lock state ] [ 66.388663] 4.9.0-rc2+ #56 Not tainted [ 66.388672] --------------------------------- [ 66.388682] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. [ 66.388695] swapper/1/0 [HC0[0]:SC1[1]:HE0:SE0] takes: [ 66.388706] (&(&b->lock)->rlock){+.?...} , at: [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.388761] {SOFTIRQ-ON-W} state was registered at: [ 66.388772] [ 66.388783] [<ffffffff810bd842>] __lock_acquire+0x682/0x1870 [ 66.388795] [ 66.388803] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.388814] [ 66.388824] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.388835] [ 66.388845] [<ffffffff81401e41>] intel_engine_reset_breadcrumbs+0x21/0xb0 [ 66.388857] [ 66.388866] [<ffffffff81403ae7>] gen8_init_common_ring+0x67/0x100 [ 66.388878] [ 66.388887] [<ffffffff81403b92>] gen8_init_render_ring+0x12/0x60 [ 66.388903] [ 66.388912] [<ffffffff813f8707>] i915_gem_init_hw+0xf7/0x2a0 [ 66.388927] [ 66.388936] [<ffffffff813f899b>] i915_gem_init+0xbb/0xf0 [ 66.388950] [ 66.388959] [<ffffffff813b4980>] i915_driver_load+0x7e0/0x1330 [ 66.388978] [ 66.388988] [<ffffffff813c09d8>] i915_pci_probe+0x28/0x40 [ 66.389003] [ 66.389013] [<ffffffff812fa0db>] pci_device_probe+0x8b/0xf0 [ 66.389028] [ 66.389037] [<ffffffff8147737e>] driver_probe_device+0x21e/0x430 [ 66.389056] [ 66.389065] [<ffffffff8147766e>] __driver_attach+0xde/0xe0 [ 66.389080] [ 66.389090] [<ffffffff814751ad>] bus_for_each_dev+0x5d/0x90 [ 66.389105] [ 66.389113] [<ffffffff81477799>] driver_attach+0x19/0x20 [ 66.389134] [ 66.389144] [<ffffffff81475ced>] bus_add_driver+0x15d/0x260 [ 66.389159] [ 66.389168] [<ffffffff81477e3b>] driver_register+0x5b/0xd0 [ 66.389183] [ 66.389281] [<ffffffff812fa19b>] __pci_register_driver+0x5b/0x60 [ 66.389301] [ 66.389312] [<ffffffff81aed333>] i915_init+0x3e/0x45 [ 66.389326] [ 66.389336] [<ffffffff81ac2ffa>] do_one_initcall+0x8b/0x118 [ 66.389350] [ 66.389359] [<ffffffff81ac323a>] kernel_init_freeable+0x1b3/0x23b [ 66.389378] [ 66.389387] [<ffffffff8160fc39>] kernel_init+0x9/0x100 [ 66.389402] [ 66.389411] [<ffffffff816180e7>] ret_from_fork+0x27/0x40 [ 66.389426] irq event stamp: 315865 [ 66.389438] hardirqs last enabled at (315864): [<ffffffff816178f1>] _raw_spin_unlock_irqrestore+0x31/0x50 [ 66.389469] hardirqs last disabled at (315865): [<ffffffff816176b3>] _raw_spin_lock_irqsave+0x13/0x50 [ 66.389499] softirqs last enabled at (315818): [<ffffffff8107a04c>] _local_bh_enable+0x1c/0x50 [ 66.389530] softirqs last disabled at (315819): [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.389559] [ 66.389559] other info that might help us debug this: [ 66.389580] Possible unsafe locking scenario: [ 66.389580] [ 66.389598] CPU0 [ 66.389609] ---- [ 66.389620] lock(&(&b->lock)->rlock); [ 66.389650] <Interrupt> [ 66.389661] lock(&(&b->lock)->rlock); [ 66.389690] [ 66.389690] *** DEADLOCK *** [ 66.389690] [ 66.389715] 2 locks held by swapper/1/0: [ 66.389728] #0: (&(&tl->lock)->rlock){..-...}, at: [<ffffffff81403e01>] intel_lrc_irq_handler+0x201/0x3c0 [ 66.389785] #1: (&(&req->lock)->rlock/1){..-...}, at: [<ffffffff813fc0af>] __i915_gem_request_submit+0x8f/0x170 [ 66.389854] [ 66.389854] stack backtrace: [ 66.389959] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.0-rc2+ #56 [ 66.389976] Hardware name: / , BIOS PYBSWCEL.86A.0027.2015.0507.1758 05/07/2015 [ 66.389999] ffff88027fd03c58 ffffffff812beae5 ffff88027696e680 ffffffff822afe20 [ 66.390036] ffff88027fd03ca8 ffffffff810bb420 0000000000000001 0000000000000000 [ 66.390070] 0000000000000000 0000000000000006 0000000000000004 ffff88027696ee10 [ 66.390104] Call Trace: [ 66.390117] <IRQ> [ 66.390128] [<ffffffff812beae5>] dump_stack+0x68/0x93 [ 66.390147] [<ffffffff810bb420>] print_usage_bug+0x1d0/0x1e0 [ 66.390164] [<ffffffff810bb8a0>] mark_lock+0x470/0x4f0 [ 66.390181] [<ffffffff810ba9d0>] ? print_shortest_lock_dependencies+0x1b0/0x1b0 [ 66.390203] [<ffffffff810bd75d>] __lock_acquire+0x59d/0x1870 [ 66.390221] [<ffffffff810bedbc>] lock_acquire+0x6c/0xb0 [ 66.390237] [<ffffffff810bedbc>] ? lock_acquire+0x6c/0xb0 [ 66.390255] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390273] [<ffffffff8161753a>] _raw_spin_lock+0x2a/0x40 [ 66.390291] [<ffffffff81401c88>] ? intel_engine_enable_signaling+0x78/0x150 [ 66.390309] [<ffffffff81401c88>] intel_engine_enable_signaling+0x78/0x150 [ 66.390327] [<ffffffff813fc170>] __i915_gem_request_submit+0x150/0x170 [ 66.390345] [<ffffffff81403e8b>] intel_lrc_irq_handler+0x28b/0x3c0 [ 66.390363] [<ffffffff81079d97>] tasklet_action+0x57/0xc0 [ 66.390380] [<ffffffff8107a249>] __do_softirq+0x119/0x240 [ 66.390396] [<ffffffff8107a50e>] irq_exit+0xbe/0xd0 [ 66.390414] [<ffffffff8101afd5>] do_IRQ+0x65/0x110 [ 66.390431] [<ffffffff81618806>] common_interrupt+0x86/0x86 [ 66.390446] <EOI> [ 66.390457] [<ffffffff814ec6d1>] ? cpuidle_enter_state+0x151/0x200 [ 66.390480] [<ffffffff814ec7a2>] cpuidle_enter+0x12/0x20 [ 66.390498] [<ffffffff810b639e>] call_cpuidle+0x1e/0x40 [ 66.390516] [<ffffffff810b65ae>] cpu_startup_entry+0x10e/0x1f0 [ 66.390534] [<ffffffff81036133>] start_secondary+0x103/0x130 (This is split out of the defer global seqno allocation patch due to realisation that we need a more complete conversion if we want to defer request submission even further.) v2: lockdep was warning about mixed SOFTIRQ contexts not HARDIRQ contexts so we only need to use spin_lock_bh and not disable interrupts. v3: We need full irq protection as we may be called from a third party interrupt handler (via fences). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161028125858.23563-32-chris@chris-wilson.co.uk
2016-10-28 20:58:55 +08:00
* against interrupts, i.e. use spin_lock_irqsave.
*/
/* locked by dma_fence_enable_sw_signaling() (irqsafe fence->lock) */
drm/i915: Assert that fence->lock is held in an irq-safe manner Everytime we take the fence->lock (aka request->lock), we must do so with irqs disabled since it may be used from within an hardirq context. As sometimes we are taking the lock in a nested manner, assert that the caller did disable the irqs for us. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170302115130.28434-1-chris@chris-wilson.co.uk Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
2017-03-02 19:51:30 +08:00
GEM_BUG_ON(!irqs_disabled());
drm/i915: s/assert_spin_locked/lockdep_assert_held/ assert_spin_locked() becomes an unconditionally compiled BUG_ON(), adding debug code right into the heart of critical routines like interrupt handlers. text data bss dec hex 1296480 19944 2272 1318696 141f28 before (lockdep disabled) 1295984 19944 2272 1318200 141d38 after 1336261 21139 3208 1360608 14c2e0 before (lockdep enabled) 1339920 21139 3208 1364267 14d12b after Small saving for release; hopefully more instructive in debug. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170302132801.599-1-chris@chris-wilson.co.uk Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
2017-03-02 21:28:01 +08:00
lockdep_assert_held(&request->lock);
drm/i915: Protect the request->global_seqno with the engine->timeline lock A request is assigned a global seqno only when it is on the hardware execution queue. The global seqno can be used to maintain a list of requests on the same engine in retirement order, for example for constructing a priority queue for waiting. Prior to its execution, or if it is subsequently removed in the event of preemption, its global seqno is zero. As both insertion and removal from the execution queue may operate in IRQ context, it is not guarded by the usual struct_mutex BKL. Instead those relying on the global seqno must be prepared for its value to change between reads. Only when the request is complete can the global seqno be stable (due to the memory barriers on submitting the commands to the hardware to write the breadcrumb, if the HWS shows that it has passed the global seqno and the global seqno is unchanged after the read, it is indeed complete). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-9-chris@chris-wilson.co.uk
2017-02-23 15:44:14 +08:00
seqno = i915_gem_request_global_seqno(request);
if (!seqno)
drm/i915: Introduce a global_seqno for each request Though we will have multiple timelines, we still have a single timeline of execution. This we can use to provide an execution and retirement order of requests. This keeps tracking execution of requests simple, and vital for preserving a single waiter (i.e. so that we can order the waiters so that only the earliest to wakeup need be woken). To accomplish this we distinguish the seqno used to order requests per-context (external) and that used internally for execution. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161028125858.23563-26-chris@chris-wilson.co.uk
2016-10-28 20:58:49 +08:00
return;
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
request->signaling.wait.tsk = b->signaler;
drm/i915: Signal first fence from irq handler if complete As execlists and other non-semaphore multi-engine devices coordinate between engines using interrupts, we can shave off a few 10s of microsecond of scheduling latency by doing the fence signaling from the interrupt as opposed to a RT kthread. (Realistically the delay adds about 1% to an individual cross-engine workload.) We only signal the first fence in order to limit the amount of work we move into the interrupt handler. We also have to remember that our breadcrumbs may be unordered with respect to the interrupt and so we still require the waiter process to perform some heavyweight coherency fixups, as well as traversing the tree of waiters. v2: No need for early exit in irq handler - it breaks the flow between patches and prevents the tracepoint v3: Restore rcu hold across irq signaling of request Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-2-chris@chris-wilson.co.uk
2017-02-28 04:58:48 +08:00
request->signaling.wait.request = request;
drm/i915: Protect the request->global_seqno with the engine->timeline lock A request is assigned a global seqno only when it is on the hardware execution queue. The global seqno can be used to maintain a list of requests on the same engine in retirement order, for example for constructing a priority queue for waiting. Prior to its execution, or if it is subsequently removed in the event of preemption, its global seqno is zero. As both insertion and removal from the execution queue may operate in IRQ context, it is not guarded by the usual struct_mutex BKL. Instead those relying on the global seqno must be prepared for its value to change between reads. Only when the request is complete can the global seqno be stable (due to the memory barriers on submitting the commands to the hardware to write the breadcrumb, if the HWS shows that it has passed the global seqno and the global seqno is unchanged after the read, it is indeed complete). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-9-chris@chris-wilson.co.uk
2017-02-23 15:44:14 +08:00
request->signaling.wait.seqno = seqno;
drm/i915: Rename request reference/unreference to get/put Now that we derive requests from struct fence, swap over to its nomenclature for references. It's shorter and more idiomatic across the kernel. s/i915_gem_request_reference/i915_gem_request_get/ s/i915_gem_request_unreference/i915_gem_request_put/ Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: http://patchwork.freedesktop.org/patch/msgid/1469005202-9659-2-git-send-email-chris@chris-wilson.co.uk Link: http://patchwork.freedesktop.org/patch/msgid/1469017917-15134-1-git-send-email-chris@chris-wilson.co.uk
2016-07-20 20:31:49 +08:00
i915_gem_request_get(request);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock(&b->rb_lock);
drm/i915: Reduce breadcrumb lock coverage for intel_engine_enable_signaling() Since intel_engine_enable_signaling() is now only called via fence_enable_sw_signaling(), we can rely on it to provide serialisation and run-once for us and so make ourselves slightly simpler. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/1469432687-22756-2-git-send-email-chris@chris-wilson.co.uk Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1469530913-17180-1-git-send-email-chris@chris-wilson.co.uk
2016-07-26 19:01:50 +08:00
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
/* First add ourselves into the list of waiters, but register our
* bottom-half as the signaller thread. As per usual, only the oldest
* waiter (not just signaller) is tasked as the bottom-half waking
* up all completed waiters after the user interrupt.
*
* If we are the oldest waiter, enable the irq (after which we
* must double check that the seqno did not complete).
*/
drm/i915: Skip waking the signaler when enabling before request submission If we are enabling the breadcrumbs signaling prior to submitting the request, we know that we cannot have missed the interrupt and can therefore skip immediately waking the signaler to check. This reduces a significant chunk of the __i915_gem_request_submit() overhead for inter-engine synchronisation, for example in gem_exec_whisper. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170426080659.28771-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2017-04-26 16:06:59 +08:00
wakeup &= __intel_engine_add_wait(engine, &request->signaling.wait);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
/* Now insert ourselves into the retirement ordered list of signals
* on this engine. We track the oldest seqno as that will be the
* first signal to complete.
*/
parent = NULL;
first = true;
p = &b->signals.rb_node;
while (*p) {
parent = *p;
drm/i915: Protect the request->global_seqno with the engine->timeline lock A request is assigned a global seqno only when it is on the hardware execution queue. The global seqno can be used to maintain a list of requests on the same engine in retirement order, for example for constructing a priority queue for waiting. Prior to its execution, or if it is subsequently removed in the event of preemption, its global seqno is zero. As both insertion and removal from the execution queue may operate in IRQ context, it is not guarded by the usual struct_mutex BKL. Instead those relying on the global seqno must be prepared for its value to change between reads. Only when the request is complete can the global seqno be stable (due to the memory barriers on submitting the commands to the hardware to write the breadcrumb, if the HWS shows that it has passed the global seqno and the global seqno is unchanged after the read, it is indeed complete). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-9-chris@chris-wilson.co.uk
2017-02-23 15:44:14 +08:00
if (i915_seqno_passed(seqno,
to_signaler(parent)->signaling.wait.seqno)) {
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
p = &parent->rb_right;
first = false;
} else {
p = &parent->rb_left;
}
}
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
rb_link_node(&request->signaling.node, parent, p);
rb_insert_color(&request->signaling.node, &b->signals);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
if (first)
drm/i915: Take a reference whilst processing the signaler request The plan in the near-future is to allow requests to be removed from the signaler. We can no longer then rely on holding a reference to the request for the duration it is in the signaling tree, and instead must obtain a reference to the request for the current operation using RCU. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
2017-02-23 15:44:15 +08:00
rcu_assign_pointer(b->first_signal, request);
drm/i915: Embed signaling node into the GEM request Under the assumption that enabling signaling will be a frequent operation, lets preallocate our attachments for signaling inside the (rather large) request struct (and so benefiting from the slab cache). v2: Convert from void * to more meaningful names and types. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-17-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:26 +08:00
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_unlock(&b->rb_lock);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
if (wakeup)
wake_up_process(b->signaler);
}
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
void intel_engine_cancel_signaling(struct drm_i915_gem_request *request)
{
struct intel_engine_cs *engine = request->engine;
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Assert that fence->lock is held in an irq-safe manner Everytime we take the fence->lock (aka request->lock), we must do so with irqs disabled since it may be used from within an hardirq context. As sometimes we are taking the lock in a nested manner, assert that the caller did disable the irqs for us. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170302115130.28434-1-chris@chris-wilson.co.uk Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
2017-03-02 19:51:30 +08:00
GEM_BUG_ON(!irqs_disabled());
drm/i915: s/assert_spin_locked/lockdep_assert_held/ assert_spin_locked() becomes an unconditionally compiled BUG_ON(), adding debug code right into the heart of critical routines like interrupt handlers. text data bss dec hex 1296480 19944 2272 1318696 141f28 before (lockdep disabled) 1295984 19944 2272 1318200 141d38 after 1336261 21139 3208 1360608 14c2e0 before (lockdep enabled) 1339920 21139 3208 1364267 14d12b after Small saving for release; hopefully more instructive in debug. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170302132801.599-1-chris@chris-wilson.co.uk Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
2017-03-02 21:28:01 +08:00
lockdep_assert_held(&request->lock);
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
GEM_BUG_ON(!request->signaling.wait.seqno);
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock(&b->rb_lock);
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
if (!RB_EMPTY_NODE(&request->signaling.node)) {
if (request == rcu_access_pointer(b->first_signal)) {
struct rb_node *rb =
rb_next(&request->signaling.node);
rcu_assign_pointer(b->first_signal,
rb ? to_signaler(rb) : NULL);
}
rb_erase(&request->signaling.node, &b->signals);
RB_CLEAR_NODE(&request->signaling.node);
i915_gem_request_put(request);
}
__intel_engine_remove_wait(engine, &request->signaling.wait);
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_unlock(&b->rb_lock);
drm/i915: Allow a request to be cancelled If we preempt a request and remove it from the execution queue, we need to undo its global seqno and restart any waiters. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-11-chris@chris-wilson.co.uk
2017-02-23 15:44:16 +08:00
request->signaling.wait.seqno = 0;
}
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
int intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
struct task_struct *tsk;
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock_init(&b->rb_lock);
spin_lock_init(&b->irq_lock);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
setup_timer(&b->fake_irq,
intel_breadcrumbs_fake_irq,
(unsigned long)engine);
drm/i915: Move missed interrupt detection from hangcheck to breadcrumbs In commit 2529d57050af ("drm/i915: Drop racy markup of missed-irqs from idle-worker") the racy detection of missed interrupts was removed when we went idle. This however opened up the issue that the stuck waiters were not being reported, causing a test case failure. If we move the stuck waiter detection out of hangcheck and into the breadcrumb mechanims (i.e. the waiter) itself, we can avoid this issue entirely. This leaves hangcheck looking for a stuck GPU (inspecting for request advancement and HEAD motion), and breadcrumbs looking for a stuck waiter - hopefully make both easier to understand by their segregation. v2: Reduce the error message as we now run independently of hangcheck, and the hanging batch used by igt also counts as a stuck waiter causing extra warnings in dmesg. v3: Move the breadcrumb's hangcheck kickstart to the first missed wait. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97104 Fixes: 2529d57050af (waiter"drm/i915: Drop racy markup of missed-irqs...") Testcase: igt/drv_missed_irq Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1470761272-1245-2-git-send-email-chris@chris-wilson.co.uk
2016-08-10 00:47:51 +08:00
setup_timer(&b->hangcheck,
intel_breadcrumbs_hangcheck,
(unsigned long)engine);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
/* Spawn a thread to provide a common bottom-half for all signals.
* As this is an asynchronous interface we cannot steal the current
* task for handling the bottom-half to the user interrupt, therefore
* we create a thread to do the coherent seqno dance after the
* interrupt and then signal the waitqueue (via the dma-buf/fence).
*/
tsk = kthread_run(intel_breadcrumbs_signaler, engine,
"i915/signal:%d", engine->id);
if (IS_ERR(tsk))
return PTR_ERR(tsk);
b->signaler = tsk;
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
return 0;
}
drm/i915: Reset the breadcrumbs IRQ more carefully Along with the interrupt, we want to restore the fake-irq and wait-timeout detection. If we use the breadcrumbs interface to setup the interrupt as it wants, the auxiliary timers will also be restored. v2: Cancel both timers as well, sanitize the IMR. Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161007065327.24515-3-chris@chris-wilson.co.uk
2016-10-07 14:53:26 +08:00
static void cancel_fake_irq(struct intel_engine_cs *engine)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
del_timer_sync(&b->hangcheck);
del_timer_sync(&b->fake_irq);
clear_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
}
void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
cancel_fake_irq(engine);
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock_irq(&b->irq_lock);
drm/i915: Reset the breadcrumbs IRQ more carefully Along with the interrupt, we want to restore the fake-irq and wait-timeout detection. If we use the breadcrumbs interface to setup the interrupt as it wants, the auxiliary timers will also be restored. v2: Cancel both timers as well, sanitize the IMR. Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161007065327.24515-3-chris@chris-wilson.co.uk
2016-10-07 14:53:26 +08:00
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
if (b->irq_enabled)
irq_enable(engine);
else
drm/i915: Reset the breadcrumbs IRQ more carefully Along with the interrupt, we want to restore the fake-irq and wait-timeout detection. If we use the breadcrumbs interface to setup the interrupt as it wants, the auxiliary timers will also be restored. v2: Cancel both timers as well, sanitize the IMR. Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161007065327.24515-3-chris@chris-wilson.co.uk
2016-10-07 14:53:26 +08:00
irq_disable(engine);
drm/i915: Delay disabling the user interrupt for breadcrumbs A significant cost in setting up a wait is the overhead of enabling the interrupt. As we disable the interrupt whenever the queue of waiters is empty, if we are frequently waiting on alternating batches, we end up re-enabling the interrupt on a frequent basis. We do want to disable the interrupt during normal operations as under high load it may add several thousand interrupts/s - we have been known in the past to occupy whole cores with our interrupt handler after accidentally leaving user interrupts enabled. As a compromise, leave the interrupt enabled until the next IRQ, or the system is idle. This gives a small window for a waiter to keep the interrupt active and not be delayed by having to re-enable the interrupt. v2: Restore hangcheck/missed-irq detection for continuations v3: Be more careful restoring the hangcheck timer after reset v4: Be more careful restoring the fake irq after reset (if required!) v5: Redo changes to intel_engine_wakeup() v6: Factor out __intel_engine_wakeup() v7: Improve commentary for declaring a missed wakeup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170227205850.2828-4-chris@chris-wilson.co.uk
2017-02-28 04:58:50 +08:00
/* We set the IRQ_BREADCRUMB bit when we enable the irq presuming the
* GPU is active and may have already executed the MI_USER_INTERRUPT
* before the CPU is ready to receive. However, the engine is currently
* idle (we haven't started it yet), there is no possibility for a
* missed interrupt as we enabled the irq and so we can clear the
* immediate wakeup (until a real interrupt arrives for the waiter).
*/
clear_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
if (b->irq_armed)
enable_fake_irq(b);
drm/i915: Reset the breadcrumbs IRQ more carefully Along with the interrupt, we want to restore the fake-irq and wait-timeout detection. If we use the breadcrumbs interface to setup the interrupt as it wants, the auxiliary timers will also be restored. v2: Cancel both timers as well, sanitize the IMR. Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161007065327.24515-3-chris@chris-wilson.co.uk
2016-10-07 14:53:26 +08:00
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_unlock_irq(&b->irq_lock);
drm/i915: Reset the breadcrumbs IRQ more carefully Along with the interrupt, we want to restore the fake-irq and wait-timeout detection. If we use the breadcrumbs interface to setup the interrupt as it wants, the auxiliary timers will also be restored. v2: Cancel both timers as well, sanitize the IMR. Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161007065327.24515-3-chris@chris-wilson.co.uk
2016-10-07 14:53:26 +08:00
}
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
drm/i915: Add a warning on shutdown if signal threads still active When unloading the module, it is expected that we have finished executing all requests and so the signal threads should be idle. Add a warning in case there are any residual requests in the signaler rbtrees at that point. v2: We can also warn if there are any waiters Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161121110759.22896-1-chris@chris-wilson.co.uk
2016-11-21 19:07:59 +08:00
/* The engines should be idle and all requests accounted for! */
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
WARN_ON(READ_ONCE(b->irq_wait));
drm/i915: Add a warning on shutdown if signal threads still active When unloading the module, it is expected that we have finished executing all requests and so the signal threads should be idle. Add a warning in case there are any residual requests in the signaler rbtrees at that point. v2: We can also warn if there are any waiters Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161121110759.22896-1-chris@chris-wilson.co.uk
2016-11-21 19:07:59 +08:00
WARN_ON(!RB_EMPTY_ROOT(&b->waiters));
drm/i915: Take a reference whilst processing the signaler request The plan in the near-future is to allow requests to be removed from the signaler. We can no longer then rely on holding a reference to the request for the duration it is in the signaling tree, and instead must obtain a reference to the request for the current operation using RCU. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
2017-02-23 15:44:15 +08:00
WARN_ON(rcu_access_pointer(b->first_signal));
drm/i915: Add a warning on shutdown if signal threads still active When unloading the module, it is expected that we have finished executing all requests and so the signal threads should be idle. Add a warning in case there are any residual requests in the signaler rbtrees at that point. v2: We can also warn if there are any waiters Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161121110759.22896-1-chris@chris-wilson.co.uk
2016-11-21 19:07:59 +08:00
WARN_ON(!RB_EMPTY_ROOT(&b->signals));
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
if (!IS_ERR_OR_NULL(b->signaler))
kthread_stop(b->signaler);
drm/i915: Reset the breadcrumbs IRQ more carefully Along with the interrupt, we want to restore the fake-irq and wait-timeout detection. If we use the breadcrumbs interface to setup the interrupt as it wants, the auxiliary timers will also be restored. v2: Cancel both timers as well, sanitize the IMR. Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161007065327.24515-3-chris@chris-wilson.co.uk
2016-10-07 14:53:26 +08:00
cancel_fake_irq(engine);
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
}
drm/i915: Keep a global seqno per-engine Replace the global device seqno with one for each engine, and account for in-flight seqno on each separately. This is consistent with dma-fence as each timeline has separate fence-contexts for each engine and a seqno is only ordered within a fence-context (i.e. seqno do not need to be ordered wrt to other engines, just ordered within a single engine). This is required to enable request rewinding for preemption on individual engines (we have to rewind the global seqno to avoid overflow, and we do not have to rewind all engines just to preempt one.) v2: Rename active_seqno to inflight_seqnos to more clearly indicate that it is a counter and not equivalent to the existing seqno. Update functions that operated on active_seqno similarly. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-3-chris@chris-wilson.co.uk
2017-02-23 15:44:08 +08:00
bool intel_breadcrumbs_busy(struct intel_engine_cs *engine)
drm/i915: Slaughter the thundering i915_wait_request herd One particularly stressful scenario consists of many independent tasks all competing for GPU time and waiting upon the results (e.g. realtime transcoding of many, many streams). One bottleneck in particular is that each client waits on its own results, but every client is woken up after every batchbuffer - hence the thunder of hooves as then every client must do its heavyweight dance to read a coherent seqno to see if it is the lucky one. Ideally, we only want one client to wake up after the interrupt and check its request for completion. Since the requests must retire in order, we can select the first client on the oldest request to be woken. Once that client has completed his wait, we can then wake up the next client and so on. However, all clients then incur latency as every process in the chain may be delayed for scheduling - this may also then cause some priority inversion. To reduce the latency, when a client is added or removed from the list, we scan the tree for completed seqno and wake up all the completed waiters in parallel. Using igt/benchmarks/gem_latency, we can demonstrate this effect. The benchmark measures the number of GPU cycles between completion of a batch and the client waking up from a call to wait-ioctl. With many concurrent waiters, with each on a different request, we observe that the wakeup latency before the patch scales nearly linearly with the number of waiters (before external factors kick in making the scaling much worse). After applying the patch, we can see that only the single waiter for the request is being woken up, providing a constant wakeup latency for every operation. However, the situation is not quite as rosy for many waiters on the same request, though to the best of my knowledge this is much less likely in practice. Here, we can observe that the concurrent waiters incur extra latency from being woken up by the solitary bottom-half, rather than directly by the interrupt. This appears to be scheduler induced (having discounted adverse effects from having a rbtree walk/erase in the wakeup path), each additional wake_up_process() costs approximately 1us on big core. Another effect of performing the secondary wakeups from the first bottom-half is the incurred delay this imposes on high priority threads - rather than immediately returning to userspace and leaving the interrupt handler to wake the others. To offset the delay incurred with additional waiters on a request, we could use a hybrid scheme that did a quick read in the interrupt handler and dequeued all the completed waiters (incurring the overhead in the interrupt handler, not the best plan either as we then incur GPU submission latency) but we would still have to wake up the bottom-half every time to do the heavyweight slow read. Or we could only kick the waiters on the seqno with the same priority as the current task (i.e. in the realtime waiter scenario, only it is woken up immediately by the interrupt and simply queues the next waiter before returning to userspace, minimising its delay at the expense of the chain, and also reducing contention on its scheduler runqueue). This is effective at avoid long pauses in the interrupt handler and at avoiding the extra latency in realtime/high-priority waiters. v2: Convert from a kworker per engine into a dedicated kthread for the bottom-half. v3: Rename request members and tweak comments. v4: Use a per-engine spinlock in the breadcrumbs bottom-half. v5: Fix race in locklessly checking waiter status and kicking the task on adding a new waiter. v6: Fix deciding when to force the timer to hide missing interrupts. v7: Move the bottom-half from the kthread to the first client process. v8: Reword a few comments v9: Break the busy loop when the interrupt is unmasked or has fired. v10: Comments, unnecessary churn, better debugging from Tvrtko v11: Wake all completed waiters on removing the current bottom-half to reduce the latency of waking up a herd of clients all waiting on the same request. v12: Rearrange missed-interrupt fault injection so that it works with igt/drv_missed_irq_hang v13: Rename intel_breadcrumb and friends to intel_wait in preparation for signal handling. v14: RCU commentary, assert_spin_locked v15: Hide BUG_ON behind the compiler; report on gem_latency findings. v16: Sort seqno-groups by priority so that first-waiter has the highest task priority (and so avoid priority inversion). v17: Add waiters to post-mortem GPU hang state. v18: Return early for a completed wait after acquiring the spinlock. Avoids adding ourselves to the tree if the is already complete, and skips the awkward question of why we don't do completion wakeups for waits earlier than or equal to ourselves. v19: Prepare for init_breadcrumbs to fail. Later patches may want to allocate during init, so be prepared to propagate back the error code. Testcase: igt/gem_concurrent_blit Testcase: igt/benchmarks/gem_latency Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: "Goel, Akash" <akash.goel@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> #v18 Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-6-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:15 +08:00
{
drm/i915: Keep a global seqno per-engine Replace the global device seqno with one for each engine, and account for in-flight seqno on each separately. This is consistent with dma-fence as each timeline has separate fence-contexts for each engine and a seqno is only ordered within a fence-context (i.e. seqno do not need to be ordered wrt to other engines, just ordered within a single engine). This is required to enable request rewinding for preemption on individual engines (we have to rewind the global seqno to avoid overflow, and we do not have to rewind all engines just to preempt one.) v2: Rename active_seqno to inflight_seqnos to more clearly indicate that it is a counter and not equivalent to the existing seqno. Update functions that operated on active_seqno similarly. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-3-chris@chris-wilson.co.uk
2017-02-23 15:44:08 +08:00
struct intel_breadcrumbs *b = &engine->breadcrumbs;
bool busy = false;
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_lock_irq(&b->rb_lock);
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
if (b->irq_wait) {
wake_up_process(b->irq_wait->tsk);
drm/i915/breadcrumbs: Use booleans for intel_breadcrumbs_busy() Since commit 9b6586ae9f6b ("drm/i915: Keep a global seqno per-engine") converted intel_breadcrumbs_busy() to reporting a single boolean, we need only compute a boolean internally (and not needlessly compute the flag). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-1-chris@chris-wilson.co.uk
2017-03-16 05:07:22 +08:00
busy = true;
drm/i915: Keep a global seqno per-engine Replace the global device seqno with one for each engine, and account for in-flight seqno on each separately. This is consistent with dma-fence as each timeline has separate fence-contexts for each engine and a seqno is only ordered within a fence-context (i.e. seqno do not need to be ordered wrt to other engines, just ordered within a single engine). This is required to enable request rewinding for preemption on individual engines (we have to rewind the global seqno to avoid overflow, and we do not have to rewind all engines just to preempt one.) v2: Rename active_seqno to inflight_seqnos to more clearly indicate that it is a counter and not equivalent to the existing seqno. Update functions that operated on active_seqno similarly. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-3-chris@chris-wilson.co.uk
2017-02-23 15:44:08 +08:00
}
drm/i915: Spin until breadcrumb threads are complete When we need to reset the global seqno on wraparound, we have to wait until the current rbtrees are drained (or otherwise the next waiter will be out of sequence). The current mechanism to kick and spin until complete, may exit too early as it would break if the target thread was currently running. Instead, we must wake up the threads, but keep spinning until the trees have been deleted. In order to appease Tvrtko, busy spin rather than yield(). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161108143719.32215-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
2016-11-08 22:37:19 +08:00
drm/i915: Take a reference whilst processing the signaler request The plan in the near-future is to allow requests to be removed from the signaler. We can no longer then rely on holding a reference to the request for the duration it is in the signaling tree, and instead must obtain a reference to the request for the current operation using RCU. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
2017-02-23 15:44:15 +08:00
if (rcu_access_pointer(b->first_signal)) {
drm/i915: Keep a global seqno per-engine Replace the global device seqno with one for each engine, and account for in-flight seqno on each separately. This is consistent with dma-fence as each timeline has separate fence-contexts for each engine and a seqno is only ordered within a fence-context (i.e. seqno do not need to be ordered wrt to other engines, just ordered within a single engine). This is required to enable request rewinding for preemption on individual engines (we have to rewind the global seqno to avoid overflow, and we do not have to rewind all engines just to preempt one.) v2: Rename active_seqno to inflight_seqnos to more clearly indicate that it is a counter and not equivalent to the existing seqno. Update functions that operated on active_seqno similarly. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-3-chris@chris-wilson.co.uk
2017-02-23 15:44:08 +08:00
wake_up_process(b->signaler);
drm/i915/breadcrumbs: Use booleans for intel_breadcrumbs_busy() Since commit 9b6586ae9f6b ("drm/i915: Keep a global seqno per-engine") converted intel_breadcrumbs_busy() to reporting a single boolean, we need only compute a boolean internally (and not needlessly compute the flag). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-1-chris@chris-wilson.co.uk
2017-03-16 05:07:22 +08:00
busy = true;
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
}
drm/i915: Split breadcrumbs spinlock into two As we now take the breadcrumbs spinlock within the interrupt handler, we wish to minimise its hold time. During the interrupt we do not care about the state of the full rbtree, only that of the first element, so we can guard that with a separate lock. v2: Rename first_wait to irq_wait to make it clearer that it is guarded by irq_lock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170303190824.1330-1-chris@chris-wilson.co.uk
2017-03-04 03:08:24 +08:00
spin_unlock_irq(&b->rb_lock);
drm/i915: Keep a global seqno per-engine Replace the global device seqno with one for each engine, and account for in-flight seqno on each separately. This is consistent with dma-fence as each timeline has separate fence-contexts for each engine and a seqno is only ordered within a fence-context (i.e. seqno do not need to be ordered wrt to other engines, just ordered within a single engine). This is required to enable request rewinding for preemption on individual engines (we have to rewind the global seqno to avoid overflow, and we do not have to rewind all engines just to preempt one.) v2: Rename active_seqno to inflight_seqnos to more clearly indicate that it is a counter and not equivalent to the existing seqno. Update functions that operated on active_seqno similarly. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-3-chris@chris-wilson.co.uk
2017-02-23 15:44:08 +08:00
return busy;
drm/i915: Convert trace-irq to the breadcrumb waiter If we convert the tracing over from direct use of ring->irq_get() and over to the breadcrumb infrastructure, we only have a single user of the ring->irq_get and so we will be able to simplify the driver routines (eliminating the redundant validation and irq refcounting). Process context is preferred over softirq (or even hardirq) for a couple of reasons: - we already utilize process context to have fast wakeup of a single client (i.e. the client waiting for the GPU inspects the seqno for itself following an interrupt to avoid the overhead of a context switch before it returns to userspace) - engine->irq_seqno() is not suitable for use from an softirq/hardirq context as we may require long waits (100-250us) to ensure the seqno write is posted before we read it from the CPU A signaling framework is a requirement for enabling dma-fences. v2: Move to a signaling framework based upon the waiter. v3: Track the first-signal to avoid having to walk the rbtree everytime. v4: Mark the signaler thread as RT priority to reduce latency in the indirect wakeups. v5: Make failure to allocate the thread fatal. v6: Rename kthreads to i915/signal:%u Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-16-git-send-email-chris@chris-wilson.co.uk
2016-07-02 00:23:25 +08:00
}
drm/i915: Add unit tests for the breadcrumb rbtree, insert/remove First retroactive test, make sure that the waiters are in global seqno order after random inserts and removals. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170213171558.20942-3-chris@chris-wilson.co.uk
2017-02-14 01:15:14 +08:00
#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
#include "selftests/intel_breadcrumbs.c"
#endif
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