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27af5eea54
Doing a lot of work in the interrupt handler introduces huge latencies to the system as a whole. Most dramatic effect can be seen by running an all engine stress test like igt/gem_exec_nop/all where, when the kernel config is lean enough, the whole system can be brought into multi-second periods of complete non-interactivty. That can look for example like this: NMI watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [kworker/u8:3:143] Modules linked in: [redacted for brevity] CPU: 0 PID: 143 Comm: kworker/u8:3 Tainted: G U L 4.5.0-160321+ #183 Hardware name: Intel Corporation Broadwell Client platform/WhiteTip Mountain 1 Workqueue: i915 gen6_pm_rps_work [i915] task: ffff8800aae88000 ti: ffff8800aae90000 task.ti: ffff8800aae90000 RIP: 0010:[<ffffffff8104a3c2>] [<ffffffff8104a3c2>] __do_softirq+0x72/0x1d0 RSP: 0000:ffff88014f403f38 EFLAGS: 00000206 RAX: ffff8800aae94000 RBX: 0000000000000000 RCX: 00000000000006e0 RDX: 0000000000000020 RSI: 0000000004208060 RDI: 0000000000215d80 RBP: ffff88014f403f80 R08: 0000000b1b42c180 R09: 0000000000000022 R10: 0000000000000004 R11: 00000000ffffffff R12: 000000000000a030 R13: 0000000000000082 R14: ffff8800aa4d0080 R15: 0000000000000082 FS: 0000000000000000(0000) GS:ffff88014f400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa53b90c000 CR3: 0000000001a0a000 CR4: 00000000001406f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Stack: 042080601b33869f ffff8800aae94000 00000000fffc2678 ffff88010000000a 0000000000000000 000000000000a030 0000000000005302 ffff8800aa4d0080 0000000000000206 ffff88014f403f90 ffffffff8104a716 ffff88014f403fa8 Call Trace: <IRQ> [<ffffffff8104a716>] irq_exit+0x86/0x90 [<ffffffff81031e7d>] smp_apic_timer_interrupt+0x3d/0x50 [<ffffffff814f3eac>] apic_timer_interrupt+0x7c/0x90 <EOI> [<ffffffffa01c5b40>] ? gen8_write64+0x1a0/0x1a0 [i915] [<ffffffff814f2b39>] ? _raw_spin_unlock_irqrestore+0x9/0x20 [<ffffffffa01c5c44>] gen8_write32+0x104/0x1a0 [i915] [<ffffffff8132c6a2>] ? n_tty_receive_buf_common+0x372/0xae0 [<ffffffffa017cc9e>] gen6_set_rps_thresholds+0x1be/0x330 [i915] [<ffffffffa017eaf0>] gen6_set_rps+0x70/0x200 [i915] [<ffffffffa0185375>] intel_set_rps+0x25/0x30 [i915] [<ffffffffa01768fd>] gen6_pm_rps_work+0x10d/0x2e0 [i915] [<ffffffff81063852>] ? finish_task_switch+0x72/0x1c0 [<ffffffff8105ab29>] process_one_work+0x139/0x350 [<ffffffff8105b186>] worker_thread+0x126/0x490 [<ffffffff8105b060>] ? rescuer_thread+0x320/0x320 [<ffffffff8105fa64>] kthread+0xc4/0xe0 [<ffffffff8105f9a0>] ? kthread_create_on_node+0x170/0x170 [<ffffffff814f351f>] ret_from_fork+0x3f/0x70 [<ffffffff8105f9a0>] ? kthread_create_on_node+0x170/0x170 I could not explain, or find a code path, which would explain a +20 second lockup, but from some instrumentation it was apparent the interrupts off proportion of time was between 10-25% under heavy load which is quite bad. When a interrupt "cliff" is reached, which was >~320k irq/s on my machine, the whole system goes into a terrible state of the above described multi-second lockups. By moving the GT interrupt handling to a tasklet in a most simple way, the problem above disappears completely. Testing the effect on sytem-wide latencies using igt/gem_syslatency shows the following before this patch: gem_syslatency: cycles=1532739, latency mean=416531.829us max=2499237us gem_syslatency: cycles=1839434, latency mean=1458099.157us max=4998944us gem_syslatency: cycles=1432570, latency mean=2688.451us max=1201185us gem_syslatency: cycles=1533543, latency mean=416520.499us max=2498886us This shows that the unrelated process is experiencing huge delays in its wake-up latency. After the patch the results look like this: gem_syslatency: cycles=808907, latency mean=53.133us max=1640us gem_syslatency: cycles=862154, latency mean=62.778us max=2117us gem_syslatency: cycles=856039, latency mean=58.079us max=2123us gem_syslatency: cycles=841683, latency mean=56.914us max=1667us Showing a huge improvement in the unrelated process wake-up latency. It also shows an approximate halving in the number of total empty batches submitted during the test. This may not be worrying since the test puts the driver under a very unrealistic load with ncpu threads doing empty batch submission to all GPU engines each. Another benefit compared to the hard-irq handling is that now work on all engines can be dispatched in parallel since we can have up to number of CPUs active tasklets. (While previously a single hard-irq would serially dispatch on one engine after another.) More interesting scenario with regards to throughput is "gem_latency -n 100" which shows 25% better throughput and CPU usage, and 14% better dispatch latencies. I did not find any gains or regressions with Synmark2 or GLbench under light testing. More benchmarking is certainly required. v2: * execlists_lock should be taken as spin_lock_bh when queuing work from userspace now. (Chris Wilson) * uncore.lock must be taken with spin_lock_irq when submitting requests since that now runs from either softirq or process context. v3: * Expanded commit message with more testing data; * converted missed locking sites to _bh; * added execlist_lock comment. (Chris Wilson) v4: * Mention dispatch parallelism in commit. (Chris Wilson) * Do not hold uncore.lock over MMIO reads since the block is already serialised per-engine via the tasklet itself. (Chris Wilson) * intel_lrc_irq_handler should be static. (Chris Wilson) * Cancel/sync the tasklet on GPU reset. (Chris Wilson) * Document and WARN that tasklet cannot be active/pending on engine cleanup. (Chris Wilson/Imre Deak) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Imre Deak <imre.deak@intel.com> Testcase: igt/gem_exec_nop/all Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94350 Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/1459768316-6670-1-git-send-email-tvrtko.ursulin@linux.intel.com |
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| dvo_ch7xxx.c | ||
| dvo_ch7017.c | ||
| dvo_ivch.c | ||
| dvo_ns2501.c | ||
| dvo_sil164.c | ||
| dvo_tfp410.c | ||
| dvo.h | ||
| i915_cmd_parser.c | ||
| i915_debugfs.c | ||
| i915_dma.c | ||
| i915_drv.c | ||
| i915_drv.h | ||
| i915_gem_batch_pool.c | ||
| i915_gem_batch_pool.h | ||
| i915_gem_context.c | ||
| i915_gem_debug.c | ||
| i915_gem_dmabuf.c | ||
| i915_gem_evict.c | ||
| i915_gem_execbuffer.c | ||
| i915_gem_fence.c | ||
| i915_gem_gtt.c | ||
| i915_gem_gtt.h | ||
| i915_gem_render_state.c | ||
| i915_gem_render_state.h | ||
| i915_gem_shrinker.c | ||
| i915_gem_stolen.c | ||
| i915_gem_tiling.c | ||
| i915_gem_userptr.c | ||
| i915_gem.c | ||
| i915_gpu_error.c | ||
| i915_guc_reg.h | ||
| i915_guc_submission.c | ||
| i915_ioc32.c | ||
| i915_irq.c | ||
| i915_params.c | ||
| i915_params.h | ||
| i915_reg.h | ||
| i915_suspend.c | ||
| i915_sysfs.c | ||
| i915_trace_points.c | ||
| i915_trace.h | ||
| i915_vgpu.c | ||
| i915_vgpu.h | ||
| intel_acpi.c | ||
| intel_atomic_plane.c | ||
| intel_atomic.c | ||
| intel_audio.c | ||
| intel_bios.c | ||
| intel_bios.h | ||
| intel_color.c | ||
| intel_crt.c | ||
| intel_csr.c | ||
| intel_ddi.c | ||
| intel_display.c | ||
| intel_dp_link_training.c | ||
| intel_dp_mst.c | ||
| intel_dp.c | ||
| intel_dpll_mgr.c | ||
| intel_dpll_mgr.h | ||
| intel_drv.h | ||
| intel_dsi_panel_vbt.c | ||
| intel_dsi_pll.c | ||
| intel_dsi.c | ||
| intel_dsi.h | ||
| intel_dvo.c | ||
| intel_fbc.c | ||
| intel_fbdev.c | ||
| intel_fifo_underrun.c | ||
| intel_frontbuffer.c | ||
| intel_guc_fwif.h | ||
| intel_guc_loader.c | ||
| intel_guc.h | ||
| intel_hdmi.c | ||
| intel_hotplug.c | ||
| intel_i2c.c | ||
| intel_lrc.c | ||
| intel_lrc.h | ||
| intel_lvds.c | ||
| intel_mocs.c | ||
| intel_mocs.h | ||
| intel_modes.c | ||
| intel_opregion.c | ||
| intel_overlay.c | ||
| intel_panel.c | ||
| intel_pm.c | ||
| intel_psr.c | ||
| intel_renderstate_gen6.c | ||
| intel_renderstate_gen7.c | ||
| intel_renderstate_gen8.c | ||
| intel_renderstate_gen9.c | ||
| intel_renderstate.h | ||
| intel_ringbuffer.c | ||
| intel_ringbuffer.h | ||
| intel_runtime_pm.c | ||
| intel_sdvo_regs.h | ||
| intel_sdvo.c | ||
| intel_sideband.c | ||
| intel_sprite.c | ||
| intel_tv.c | ||
| intel_uncore.c | ||
| intel_vbt_defs.h | ||
| Kconfig | ||
| Kconfig.debug | ||
| Makefile | ||