preempt_disable() and local_irq_disable/save() are in principle per CPU big
kernel locks. This has several downsides:
- The protection scope is unknown
- Violation of protection rules is hard to detect by instrumentation
- For PREEMPT_RT such sections, unless in low level critical code, can
violate the preemptability constraints.
To address this PREEMPT_RT introduced the concept of local_locks which are
strictly per CPU.
The lock operations map to preempt_disable(), local_irq_disable/save() and
the enabling counterparts on non RT enabled kernels.
If lockdep is enabled local locks gain a lock map which tracks the usage
context. This will catch cases where an area is protected by
preempt_disable() but the access also happens from interrupt context. local
locks have identified quite a few such issues over the years, the most
recent example is:
b7d5dc2107 ("random: add a spinlock_t to struct batched_entropy")
Aside of the lockdep coverage this also improves code readability as it
precisely annotates the protection scope.
PREEMPT_RT substitutes these local locks with 'sleeping' spinlocks to
protect such sections while maintaining preemtability and CPU locality.
local locks can replace:
- preempt_enable()/disable() pairs
- local_irq_disable/enable() pairs
- local_irq_save/restore() pairs
They are also used to replace code which implicitly disables preemption
like:
- get_cpu()/put_cpu()
- get_cpu_var()/put_cpu_var()
with PREEMPT_RT friendly constructs.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-2-bigeasy@linutronix.de
Minor editorial fixes:
- remove 'enabled' from PREEMPT_RT enabled kernels for consistency
- add some periods for consistency
- add "'" for possessive CPU's
- spell out interrupts
[ tglx: Picked up Paul's suggestions ]
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/ac615f36-0b44-408d-aeab-d76e4241add4@infradead.org
The documentation of rw_semaphores is wrong as it claims that the non-owner
reader release is not supported by RT. That's just history biased memory
distortion.
Split the 'Owner semantics' section up and add separate sections for
semaphore and rw_semaphore to reflect reality.
Aside of that the following updates are done:
- Add pseudo code to document the spinlock state preserving mechanism on
PREEMPT_RT
- Wordsmith the bitspinlock and lock nesting sections
Co-developed-by: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/87wo78y5yy.fsf@nanos.tec.linutronix.de
The kernel provides a variety of locking primitives. The nesting of these
lock types and the implications of them on RT enabled kernels is nowhere
documented.
Add initial documentation.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.026561244@linutronix.de
Commit 2e4f5382d1 ("locking/doc: Rename LOCK/UNLOCK to
ACQUIRE/RELEASE") has not appied to 'spinlock.rst'. This commit updates
the doc for the change.
Signed-off-by: SeongJae Park <sjpark@amazon.com>
Link: https://lore.kernel.org/r/20200131205237.29535-2-sj38.park@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Remove the clever example about read-write lock because this type of
lock is not recommended anymore (according to the very same document).
So there is no reason to teach clever things that people should not do.
Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Some files got renamed but probably due to some merge conflicts,
a few references still point to the old locations.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Convert the locking documents to ReST and add them to the
kernel development book where it belongs.
Most of the stuff here is just to make Sphinx to properly
parse the text file, as they're already in good shape,
not requiring massive changes in order to be parsed.
The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.
At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Federico Vaga <federico.vaga@vaga.pv.it>
More words are added to lockdep design document regarding key concepts,
which should help people without lockdep experience read and understand
lockdep reports.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-3-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Since the removal of FS_RECLAIM annotations, lockdep states contain four
characters, not six.
Fixes: e5684bbfc3 ("Documentation/locking/lockdep: Update info about states")
Fixes: d92a8cfcb3 ("locking/lockdep: Rework FS_RECLAIM annotation")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
readability improvements for the formatted output, some LICENSES updates
including the addition of the ISC license, the removal of the unloved and
unmaintained 00-INDEX files, the deprecated APIs document from Kees, more
MM docs from Mike Rapoport, and the usual pile of typo fixes and
corrections.
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Merge tag 'docs-4.20' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"This is a fairly typical cycle for documentation. There's some welcome
readability improvements for the formatted output, some LICENSES
updates including the addition of the ISC license, the removal of the
unloved and unmaintained 00-INDEX files, the deprecated APIs document
from Kees, more MM docs from Mike Rapoport, and the usual pile of typo
fixes and corrections"
* tag 'docs-4.20' of git://git.lwn.net/linux: (41 commits)
docs: Fix typos in histogram.rst
docs: Introduce deprecated APIs list
kernel-doc: fix declaration type determination
doc: fix a typo in adding-syscalls.rst
docs/admin-guide: memory-hotplug: remove table of contents
doc: printk-formats: Remove bogus kobject references for device nodes
Documentation: preempt-locking: Use better example
dm flakey: Document "error_writes" feature
docs/completion.txt: Fix a couple of punctuation nits
LICENSES: Add ISC license text
LICENSES: Add note to CDDL-1.0 license that it should not be used
docs/core-api: memory-hotplug: add some details about locking internals
docs/core-api: rename memory-hotplug-notifier to memory-hotplug
docs: improve readability for people with poorer eyesight
yama: clarify ptrace_scope=2 in Yama documentation
docs/vm: split memory hotplug notifier description to Documentation/core-api
docs: move memory hotplug description into admin-guide/mm
doc: Fix acronym "FEKEK" in ecryptfs
docs: fix some broken documentation references
iommu: Fix passthrough option documentation
...
Fix incorrect line number in example output
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Cc: Jiri Kosina <trivial@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/1538391663-54524-1-git-send-email-andrew.murray@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This is a respin with a wider audience (all that get_maintainer returned)
and I know this spams a *lot* of people. Not sure what would be the correct
way, so my apologies for ruining your inbox.
The 00-INDEX files are supposed to give a summary of all files present
in a directory, but these files are horribly out of date and their
usefulness is brought into question. Often a simple "ls" would reveal
the same information as the filenames are generally quite descriptive as
a short introduction to what the file covers (it should not surprise
anyone what Documentation/sched/sched-design-CFS.txt covers)
A few years back it was mentioned that these files were no longer really
needed, and they have since then grown further out of date, so perhaps
it is time to just throw them out.
A short status yields the following _outdated_ 00-INDEX files, first
counter is files listed in 00-INDEX but missing in the directory, last
is files present but not listed in 00-INDEX.
List of outdated 00-INDEX:
Documentation: (4/10)
Documentation/sysctl: (0/1)
Documentation/timers: (1/0)
Documentation/blockdev: (3/1)
Documentation/w1/slaves: (0/1)
Documentation/locking: (0/1)
Documentation/devicetree: (0/5)
Documentation/power: (1/1)
Documentation/powerpc: (0/5)
Documentation/arm: (1/0)
Documentation/x86: (0/9)
Documentation/x86/x86_64: (1/1)
Documentation/scsi: (4/4)
Documentation/filesystems: (2/9)
Documentation/filesystems/nfs: (0/2)
Documentation/cgroup-v1: (0/2)
Documentation/kbuild: (0/4)
Documentation/spi: (1/0)
Documentation/virtual/kvm: (1/0)
Documentation/scheduler: (0/2)
Documentation/fb: (0/1)
Documentation/block: (0/1)
Documentation/networking: (6/37)
Documentation/vm: (1/3)
Then there are 364 subdirectories in Documentation/ with several files that
are missing 00-INDEX alltogether (and another 120 with a single file and no
00-INDEX).
I don't really have an opinion to whether or not we /should/ have 00-INDEX,
but the above 00-INDEX should either be removed or be kept up to date. If
we should keep the files, I can try to keep them updated, but I rather not
if we just want to delete them anyway.
As a starting point, remove all index-files and references to 00-INDEX and
see where the discussion is going.
Signed-off-by: Henrik Austad <henrik@austad.us>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Just-do-it-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: [Almost everybody else]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The current Wound-Wait mutex algorithm is actually not Wound-Wait but
Wait-Die. Implement also Wound-Wait as a per-ww-class choice. Wound-Wait
is, contrary to Wait-Die a preemptive algorithm and is known to generate
fewer backoffs. Testing reveals that this is true if the
number of simultaneous contending transactions is small.
As the number of simultaneous contending threads increases, Wait-Wound
becomes inferior to Wait-Die in terms of elapsed time.
Possibly due to the larger number of held locks of sleeping transactions.
Update documentation and callers.
Timings using git://people.freedesktop.org/~thomash/ww_mutex_test
tag patch-18-06-15
Each thread runs 100000 batches of lock / unlock 800 ww mutexes randomly
chosen out of 100000. Four core Intel x86_64:
Algorithm #threads Rollbacks time
Wound-Wait 4 ~100 ~17s.
Wait-Die 4 ~150000 ~19s.
Wound-Wait 16 ~360000 ~109s.
Wait-Die 16 ~450000 ~82s.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Co-authored-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Make the WW mutex code more readable by adding comments, splitting up
functions and pointing out that we're actually using the Wait-Die
algorithm.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Co-authored-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Add section about annotations that can be used to perform additional runtime
checking of locking correctness: assert that certain locks are held and
prevent accidental unlocking.
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/20180213185519.18186-3-juri.lelli@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Commit:
d92a8cfcb3 ("locking/lockdep: Rework FS_RECLAIM annotation")
removed the 'reclaim_fs' lockdep STATE.
Reflect the change in the documentation.
While we are at it, also clarify the formula to calculate the number of state bits.
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/20180213185519.18186-2-juri.lelli@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Commit 3ca0ff571b ("locking/mutex: Rework mutex::owner") reworked the
basic mutex implementation to deal with several problems. Documentation
was however left unchanged and became stale.
Update mutex-design.txt to reflect changes introduced by the above commit.
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/20180209160114.19980-1-juri.lelli@redhat.com
[ Small readability tweaks to the text. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull RCU updates from Paul E. McKenney:
- Updates to use cond_resched() instead of cond_resched_rcu_qs()
where feasible (currently everywhere except in kernel/rcu and
in kernel/torture.c). Also a couple of fixes to avoid sending
IPIs to offline CPUs.
- Updates to simplify RCU's dyntick-idle handling.
- Updates to remove almost all uses of smp_read_barrier_depends()
and read_barrier_depends().
- Miscellaneous fixes.
- Torture-test updates.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This code (CONFIG_LOCKDEP_CROSSRELEASE=y and CONFIG_LOCKDEP_COMPLETIONS=y),
while it found a number of old bugs initially, was also causing too many
false positives that caused people to disable lockdep - which is arguably
a worse overall outcome.
If we disable cross-release by default but keep the code upstream then
in practice the most likely outcome is that we'll allow the situation
to degrade gradually, by allowing entropy to introduce more and more
false positives, until it overwhelms maintenance capacity.
Another bad side effect was that people were trying to work around
the false positives by uglifying/complicating unrelated code. There's
a marked difference between annotating locking operations and
uglifying good code just due to bad lock debugging code ...
This gradual decrease in quality happened to a number of debugging
facilities in the kernel, and lockdep is pretty complex already,
so we cannot risk this outcome.
Either cross-release checking can be done right with no false positives,
or it should not be included in the upstream kernel.
( Note that it might make sense to maintain it out of tree and go through
the false positives every now and then and see whether new bugs were
introduced. )
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
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>
The purpose of torture_runnable is to allow rcutorture and locktorture
to be started and stopped via sysfs when they are built into the kernel
(as in not compiled as loadable modules). However, the 0444 permissions
for both instances of torture_runnable prevent this use case from ever
being put into practice. Given that there have been no complaints
about this deficiency, it is reasonable to conclude that no one actually
makes use of this sysfs capability. The perf_runnable module parameter
for rcuperf is in the same situation.
This commit therefore removes both torture_runnable instances as well
as perf_runnable.
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The rtmutex remove a pending owner bit in in rt_mutex::owner, in
commit 8161239a8b ("rtmutex: Simplify PI algorithm and make highest prio task get lock")
But the document was changed accordingly. Updating it to a meaningful
state.
BTW, as 'Steven Rostedt' mentioned:
There is still technically a "Pending Owner", it's just not called
that anymore. The pending owner happens to be the top_waiter of a lock
that has no owner and has been woken up to grab the lock.
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
To: linux-doc@vger.kernel.org
To: linux-kernel@vger.kernel.org
To: Jonathan Corbet <corbet@lwn.net>
To: Ingo Molnar <mingo@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The rt-mutex-design documents didn't gotten meaningful update from its
first version. Even after owner's pending bit was removed in commit 8161239a8b
("rtmutex: Simplify PI algorithm and make highest prio task get lock")
and priority list 'plist' changed to rbtree. And Peter Zijlstra did some
clean up and fix for deadline task changes on tip tree.
So update it to latest code and make it meaningful.
Steven Rostedt and Sebastian Siewior gave much of comments and input
in this doc. Thanks!
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
To: linux-doc@vger.kernel.org
To: linux-kernel@vger.kernel.org
To: Jonathan Corbet <corbet@lwn.net>
To: Ingo Molnar <mingo@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Document the invariants we maintain for the wait list of ww_mutexes.
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-13-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
It is now unused, remove it before someone else thinks its a good idea
to use this.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
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>
Pull locking changes from Ingo Molnar:
"The main changes in this cycle were:
- More gradual enhancements to atomic ops: new atomic*_read_ctrl()
ops, synchronize atomic_{read,set}() ordering requirements between
architectures, add atomic_long_t bitops. (Peter Zijlstra)
- Add _{relaxed|acquire|release}() variants for inc/dec atomics and
use them in various locking primitives: mutex, rtmutex, mcs, rwsem.
This enables weakly ordered architectures (such as arm64) to make
use of more locking related optimizations. (Davidlohr Bueso)
- Implement atomic[64]_{inc,dec}_relaxed() on ARM. (Will Deacon)
- Futex kernel data cache footprint micro-optimization. (Rasmus
Villemoes)
- pvqspinlock runtime overhead micro-optimization. (Waiman Long)
- misc smaller fixlets"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
ARM, locking/atomics: Implement _relaxed variants of atomic[64]_{inc,dec}
locking/rwsem: Use acquire/release semantics
locking/mcs: Use acquire/release semantics
locking/rtmutex: Use acquire/release semantics
locking/mutex: Use acquire/release semantics
locking/asm-generic: Add _{relaxed|acquire|release}() variants for inc/dec atomics
atomic: Implement atomic_read_ctrl()
atomic, arch: Audit atomic_{read,set}()
atomic: Add atomic_long_t bitops
futex: Force hot variables into a single cache line
locking/pvqspinlock: Kick the PV CPU unconditionally when _Q_SLOW_VAL
locking/osq: Relax atomic semantics
locking/qrwlock: Rename ->lock to ->wait_lock
locking/Documentation/lockstat: Fix typo - lokcing -> locking
locking/atomics, cmpxchg: Privatize the inclusion of asm/cmpxchg.h
Real time mutexes is one of the few general primitives
that we do not have in locktorture. Address this -- a few
considerations:
o To spice things up, enable competing thread(s) to become
rt, such that we can stress different prio boosting paths
in the rtmutex code. Introduce a ->task_boost callback,
only used by rtmutex-torturer. Tasks will boost/deboost
around every 50k (arbitrarily) lock/unlock operations.
o Hold times are similar to what we have for other locks:
only occasionally having longer hold times (per ~200k ops).
So we roughly do two full rt boost+deboosting ops with
short hold times.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Highlights this time around include:
- A thrashing of SubmittingPatches to bring it out of the "send everything
to Linus" era of kernel development.
- A new document on completions from Nicholas McGuire
- Lots of typo fixes, formatting improvements, corrections, build fixes,
and more.
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Merge tag 'docs-for-linus' of git://git.lwn.net/linux-2.6
Pull documentation updates from Jonathan Corbet:
"Highlights this time around include:
- A thrashing of SubmittingPatches to bring it out of the "send
everything to Linus" era of kernel development.
- A new document on completions from Nicholas McGuire
- Lots of typo fixes, formatting improvements, corrections, build
fixes, and more"
* tag 'docs-for-linus' of git://git.lwn.net/linux-2.6: (35 commits)
Documentation: Fix the wrong command `echo -1 > set_ftrace_pid` for cleaning the filter.
can-doc: Fixed a wrong filepath in can.txt
Documentation: Fix trivial typo in comment.
kgdb,docs: Fix typo and minor style issues
Documentation: add description for FTRACE probe status
doc: brief user documentation for completion
Documentation/misc-devices/mei: Fix indentation of embedded code.
Documentation/misc-devices/mei: Fix indentation of enumeration.
Documentation/misc-devices/mei: Fix spacing around parentheses.
Documentation/misc-devices/mei: Fix formatting of headings.
Documentation: devicetree: Fix double words in Doumentation/devicetree
Documentation: mm: Fix typo in vm.txt
lockstat: Add documentation on contention and contenting points
Documentation: fix blackfin gptimers-example build errors
Fixes column alignment in table of contents entry 1.9 in Documentation/filesystems/proc.txt
CodingStyle: enable emacs display of trailing whitespace
DocBook: Do not exceed argument list limit
gpio: board.txt: Fix the gpio name example
Documentation/SubmittingPatches: unify whitespace/tabs for the DCO
MAINTAINERS: Add the docs-next git tree to the maintainer entry
...
Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
lockdep code has been moved from kernel/ to kernel/locking/ by commit
8eddac3f10 ("locking: Move the lockdep
code to kernel/locking/"). But, path to lockdep code in document was not
updated.
This commit updates the path.
Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1421176921-27688-1-git-send-email-sj38.park@gmail.com
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Added files
- hsi.txt was added by 3a8ab8af (HSI: Add some general description for
the HSI subsystem)
- lzo.txt was added by d98a0526 (lzo: document part of the encoding)
- xillybus.txt was added by 7051924f (xillybus: Move out of staging)
- mailbox.txt was added by 15320fbc (add documentation for mailbox
framework)
Moved files
- xommit 214e0aed (Move locking related docs into Documentation/locking/):
* lockdep-design.txt
* lockstat.txt
* mutex-design.txt
* rt-mutex-design.txt
* rt-mutex.txt
* spinlocks.txt
* ww-mutex-design.txt
- kselftest.txt was moved by 3c415707 (kselftest: Move the docs to the
Documentation dir)
CC: Davidlohr Bueso <davidlohr@hp.com>
CC: Willy Tarreau <w@1wt.eu>
CC: Randy Dunlap <rdunlap@infradead.org>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Sebastian Reichel <sre@kernel.org>
CC: Eli Billauer <eli.billauer@gmail.com>
CC: Jonathan Corbet <corbet@lwn.net>
CC: Jiri Kosina <trivial@kernel.org>
CC: linux-doc@vger.kernel.org
CC: linux-kernel@vger.kernel.org
Cc: Tim Bird <tim.bird@sonymobile.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Henrik Austad <henrik@austad.us>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Pull locking tree changes from Ingo Molnar:
"Two changes: a documentation update and a ticket locks live lock fix"
* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/ticketlock: Fix spin_unlock_wait() livelock
locking/lglocks: Add documentation of current lglocks implementation
Local/global locks are currently not documented anywhere other
than in an somewhat out-of-date LWN article - this is an attempt
to document the current state of lglocks.
This patch is against linux-next 3.18.0-rc6
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Carsten Emde <c.emde@osadl.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20141208083326.GA29895@opentech.at
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull core locking updates from Ingo Molnar:
"The main updates in this cycle were:
- mutex MCS refactoring finishing touches: improve comments, refactor
and clean up code, reduce debug data structure footprint, etc.
- qrwlock finishing touches: remove old code, self-test updates.
- small rwsem optimization
- various smaller fixes/cleanups"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking/lockdep: Revert qrwlock recusive stuff
locking/rwsem: Avoid double checking before try acquiring write lock
locking/rwsem: Move EXPORT_SYMBOL() lines to follow function definition
locking/rwlock, x86: Delete unused asm/rwlock.h and rwlock.S
locking/rwlock, x86: Clean up asm/spinlock*.h to remove old rwlock code
locking/semaphore: Resolve some shadow warnings
locking/selftest: Support queued rwlock
locking/lockdep: Restrict the use of recursive read_lock() with qrwlock
locking/spinlocks: Always evaluate the second argument of spin_lock_nested()
locking/Documentation: Update locking/mutex-design.txt disadvantages
locking/Documentation: Move locking related docs into Documentation/locking/
locking/mutexes: Use MUTEX_SPIN_ON_OWNER when appropriate
locking/mutexes: Refactor optimistic spinning code
locking/mcs: Remove obsolete comment
locking/mutexes: Document quick lock release when unlocking
locking/mutexes: Standardize arguments in lock/unlock slowpaths
locking: Remove deprecated smp_mb__() barriers
Add a "rw_lock" torture test to stress kernel rwlocks and their irq
variant. Reader critical regions are 5x longer than writers. As such
a similar ratio of lock acquisitions is seen in the statistics. In the
case of massive contention, both hold the lock for 1/10 of a second.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
We can easily do so with our new reader lock support. Just an arbitrary
design default: readers have higher (5x) critical region latencies than
writers: 50 ms and 10 ms, respectively.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Most of it is based on what we already have for writers. This allows
readers to be very independent (and thus configurable), enabling
future module parameters to control things such as rw distribution.
Furthermore, readers have their own delaying function, allowing us
to test different rw critical region latencies, and stress locking
internals. Similarly, statistics, for now will only serve for the
number of lock acquisitions -- as opposed to writers, readers have
no failure detection.
In addition, introduce a new nreaders_stress module parameter. The
default number of readers will be the same number of writers threads.
Writer threads are interleaved with readers. Documentation is updated,
respectively.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Add a "mutex_lock" torture test. The main difference with the already
existing spinlock tests is that the latency of the critical region
is much larger. We randomly delay for (arbitrarily) either 500 ms or,
otherwise, 25 ms. While this can considerably reduce the amount of
writes compared to non blocking locks, if run long enough it can have
the same torturous effect. Furthermore it is more representative of
mutex hold times and can stress better things like thrashing.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Just like Documentation/RCU/torture.txt, begin a document for the
locktorture module. This module is still pretty green, so I have
just added some specific sections to the doc (general desc, params,
usage, etc.). Further development should update the file.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
[ paulmck: Apply Randy Dunlap review comments. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Fortunately Jason was able to reduce some of the overhead we
had introduced in the original rwsem optimistic spinning -
an it is now the same size as mutexes. Update the documentation
accordingly.
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Acked-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: aswin@hp.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Link: http://lkml.kernel.org/r/1406752916-3341-7-git-send-email-davidlohr@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
