linux/kernel/locking/lock_events_list.h

70 lines
3.1 KiB
C
Raw Normal View History

/* SPDX-License-Identifier: GPL-2.0 */
/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* Authors: Waiman Long <longman@redhat.com>
*/
#ifndef LOCK_EVENT
#define LOCK_EVENT(name) LOCKEVENT_ ## name,
#endif
#ifdef CONFIG_QUEUED_SPINLOCKS
#ifdef CONFIG_PARAVIRT_SPINLOCKS
/*
* Locking events for PV qspinlock.
*/
LOCK_EVENT(pv_hash_hops) /* Average # of hops per hashing operation */
LOCK_EVENT(pv_kick_unlock) /* # of vCPU kicks issued at unlock time */
LOCK_EVENT(pv_kick_wake) /* # of vCPU kicks for pv_latency_wake */
LOCK_EVENT(pv_latency_kick) /* Average latency (ns) of vCPU kick */
LOCK_EVENT(pv_latency_wake) /* Average latency (ns) of kick-to-wakeup */
LOCK_EVENT(pv_lock_stealing) /* # of lock stealing operations */
LOCK_EVENT(pv_spurious_wakeup) /* # of spurious wakeups in non-head vCPUs */
LOCK_EVENT(pv_wait_again) /* # of wait's after queue head vCPU kick */
LOCK_EVENT(pv_wait_early) /* # of early vCPU wait's */
LOCK_EVENT(pv_wait_head) /* # of vCPU wait's at the queue head */
LOCK_EVENT(pv_wait_node) /* # of vCPU wait's at non-head queue node */
#endif /* CONFIG_PARAVIRT_SPINLOCKS */
/*
* Locking events for qspinlock
*
* Subtracting lock_use_node[234] from lock_slowpath will give you
* lock_use_node1.
*/
LOCK_EVENT(lock_pending) /* # of locking ops via pending code */
LOCK_EVENT(lock_slowpath) /* # of locking ops via MCS lock queue */
LOCK_EVENT(lock_use_node2) /* # of locking ops that use 2nd percpu node */
LOCK_EVENT(lock_use_node3) /* # of locking ops that use 3rd percpu node */
LOCK_EVENT(lock_use_node4) /* # of locking ops that use 4th percpu node */
LOCK_EVENT(lock_no_node) /* # of locking ops w/o using percpu node */
#endif /* CONFIG_QUEUED_SPINLOCKS */
locking/rwsem: Enable lock event counting Add lock event counting calls so that we can track the number of lock events happening in the rwsem code. With CONFIG_LOCK_EVENT_COUNTS on and booting a 4-socket 112-thread x86-64 system, the rwsem counts after system bootup were as follows: rwsem_opt_fail=261 rwsem_opt_wlock=50636 rwsem_rlock=445 rwsem_rlock_fail=0 rwsem_rlock_fast=22 rwsem_rtrylock=810144 rwsem_sleep_reader=441 rwsem_sleep_writer=310 rwsem_wake_reader=355 rwsem_wake_writer=2335 rwsem_wlock=261 rwsem_wlock_fail=0 rwsem_wtrylock=20583 It can be seen that most of the lock acquisitions in the slowpath were write-locks in the optimistic spinning code path with no sleeping at all. For this system, over 97% of the locks are acquired via optimistic spinning. It illustrates the importance of optimistic spinning in improving the performance of rwsem. Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Davidlohr Bueso <dbueso@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Davidlohr Bueso <dave@stgolabs.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: Tim Chen <tim.c.chen@linux.intel.com> Cc: Will Deacon <will.deacon@arm.com> Link: http://lkml.kernel.org/r/20190404174320.22416-11-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-04 17:43:19 +00:00
/*
* Locking events for rwsem
*/
LOCK_EVENT(rwsem_sleep_reader) /* # of reader sleeps */
LOCK_EVENT(rwsem_sleep_writer) /* # of writer sleeps */
LOCK_EVENT(rwsem_wake_reader) /* # of reader wakeups */
LOCK_EVENT(rwsem_wake_writer) /* # of writer wakeups */
locking/rwsem: Remove reader optimistic spinning Reader optimistic spinning is helpful when the reader critical section is short and there aren't that many readers around. It also improves the chance that a reader can get the lock as writer optimistic spinning disproportionally favors writers much more than readers. Since commit d3681e269fff ("locking/rwsem: Wake up almost all readers in wait queue"), all the waiting readers are woken up so that they can all get the read lock and run in parallel. When the number of contending readers is large, allowing reader optimistic spinning will likely cause reader fragmentation where multiple smaller groups of readers can get the read lock in a sequential manner separated by writers. That reduces reader parallelism. One possible way to address that drawback is to limit the number of readers (preferably one) that can do optimistic spinning. These readers act as representatives of all the waiting readers in the wait queue as they will wake up all those waiting readers once they get the lock. Alternatively, as reader optimistic lock stealing has already enhanced fairness to readers, it may be easier to just remove reader optimistic spinning and simplifying the optimistic spinning code as a result. Performance measurements (locking throughput kops/s) using a locking microbenchmark with 50/50 reader/writer distribution and turbo-boost disabled was done on a 2-socket Cascade Lake system (48-core 96-thread) to see the impacts of these changes: 1) Vanilla - 5.10-rc3 kernel 2) Before - 5.10-rc3 kernel with previous patches in this series 2) limit-rspin - 5.10-rc3 kernel with limited reader spinning patch 3) no-rspin - 5.10-rc3 kernel with reader spinning disabled # of threads CS Load Vanilla Before limit-rspin no-rspin ------------ ------- ------- ------ ----------- -------- 2 1 5,185 5,662 5,214 5,077 4 1 5,107 4,983 5,188 4,760 8 1 4,782 4,564 4,720 4,628 16 1 4,680 4,053 4,567 3,402 32 1 4,299 1,115 1,118 1,098 64 1 3,218 983 1,001 957 96 1 1,938 944 957 930 2 20 2,008 2,128 2,264 1,665 4 20 1,390 1,033 1,046 1,101 8 20 1,472 1,155 1,098 1,213 16 20 1,332 1,077 1,089 1,122 32 20 967 914 917 980 64 20 787 874 891 858 96 20 730 836 847 844 2 100 372 356 360 355 4 100 492 425 434 392 8 100 533 537 529 538 16 100 548 572 568 598 32 100 499 520 527 537 64 100 466 517 526 512 96 100 406 497 506 509 The column "CS Load" represents the number of pause instructions issued in the locking critical section. A CS load of 1 is extremely short and is not likey in real situations. A load of 20 (moderate) and 100 (long) are more realistic. It can be seen that the previous patches in this series have reduced performance in general except in highly contended cases with moderate or long critical sections that performance improves a bit. This change is mostly caused by the "Prevent potential lock starvation" patch that reduce reader optimistic spinning and hence reduce reader fragmentation. The patch that further limit reader optimistic spinning doesn't seem to have too much impact on overall performance as shown in the benchmark data. The patch that disables reader optimistic spinning shows reduced performance at lightly loaded cases, but comparable or slightly better performance on with heavier contention. This patch just removes reader optimistic spinning for now. As readers are not going to do optimistic spinning anymore, we don't need to consider if the OSQ is empty or not when doing lock stealing. Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Davidlohr Bueso <dbueso@suse.de> Link: https://lkml.kernel.org/r/20201121041416.12285-6-longman@redhat.com
2020-11-21 04:14:16 +00:00
LOCK_EVENT(rwsem_opt_lock) /* # of opt-acquired write locks */
locking/rwsem: Adaptive disabling of reader optimistic spinning Reader optimistic spinning is helpful when the reader critical section is short and there aren't that many readers around. It makes readers relatively more preferred than writers. When a writer times out spinning on a reader-owned lock and set the nospinnable bits, there are two main reasons for that. 1) The reader critical section is long, perhaps the task sleeps after acquiring the read lock. 2) There are just too many readers contending the lock causing it to take a while to service all of them. In the former case, long reader critical section will impede the progress of writers which is usually more important for system performance. In the later case, reader optimistic spinning tends to make the reader groups that contain readers that acquire the lock together smaller leading to more of them. That may hurt performance in some cases. In other words, the setting of nonspinnable bits indicates that reader optimistic spinning may not be helpful for those workloads that cause it. Therefore, any writers that have observed the setting of the writer nonspinnable bit for a given rwsem after they fail to acquire the lock via optimistic spinning will set the reader nonspinnable bit once they acquire the write lock. Similarly, readers that observe the setting of reader nonspinnable bit at slowpath entry will also set the reader nonspinnable bit when they acquire the read lock via the wakeup path. Once the reader nonspinnable bit is on, it will only be reset when a writer is able to acquire the rwsem in the fast path or somehow a reader or writer in the slowpath doesn't observe the nonspinable bit. This is to discourage reader optmistic spinning on that particular rwsem and make writers more preferred. This adaptive disabling of reader optimistic spinning will alleviate some of the negative side effect of this feature. In addition, this patch tries to make readers in the spinning queue follow the phase-fair principle after quitting optimistic spinning by checking if another reader has somehow acquired a read lock after this reader enters the optimistic spinning queue. If so and the rwsem is still reader-owned, this reader is in the right read-phase and can attempt to acquire the lock. On a 2-socket 40-core 80-thread Skylake system, the page_fault1 test of the will-it-scale benchmark was run with various number of threads. The number of operations done before reader optimistic spinning patches, this patch and after this patch were: Threads Before rspin Before patch After patch %change ------- ------------ ------------ ----------- ------- 20 5541068 5345484 5455667 -3.5%/ +2.1% 40 10185150 7292313 9219276 -28.5%/+26.4% 60 8196733 6460517 7181209 -21.2%/+11.2% 80 9508864 6739559 8107025 -29.1%/+20.3% This patch doesn't recover all the lost performance, but it is more than half. Given the fact that reader optimistic spinning does benefit some workloads, this is a good compromise. Using the rwsem locking microbenchmark with very short critical section, this patch doesn't have too much impact on locking performance as shown by the locking rates (kops/s) below with equal numbers of readers and writers before and after this patch: # of Threads Pre-patch Post-patch ------------ --------- ---------- 2 4,730 4,969 4 4,814 4,786 8 4,866 4,815 16 4,715 4,511 32 3,338 3,500 64 3,212 3,389 80 3,110 3,044 When running the locking microbenchmark with 40 dedicated reader and writer threads, however, the reader performance is curtailed to favor the writer. Before patch: 40 readers, Iterations Min/Mean/Max = 204,026/234,309/254,816 40 writers, Iterations Min/Mean/Max = 88,515/95,884/115,644 After patch: 40 readers, Iterations Min/Mean/Max = 33,813/35,260/36,791 40 writers, Iterations Min/Mean/Max = 95,368/96,565/97,798 Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Will Deacon <will.deacon@arm.com> Cc: huang ying <huang.ying.caritas@gmail.com> Link: https://lkml.kernel.org/r/20190520205918.22251-16-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-05-20 20:59:14 +00:00
LOCK_EVENT(rwsem_opt_fail) /* # of failed optspins */
LOCK_EVENT(rwsem_opt_nospin) /* # of disabled optspins */
locking/rwsem: Enable lock event counting Add lock event counting calls so that we can track the number of lock events happening in the rwsem code. With CONFIG_LOCK_EVENT_COUNTS on and booting a 4-socket 112-thread x86-64 system, the rwsem counts after system bootup were as follows: rwsem_opt_fail=261 rwsem_opt_wlock=50636 rwsem_rlock=445 rwsem_rlock_fail=0 rwsem_rlock_fast=22 rwsem_rtrylock=810144 rwsem_sleep_reader=441 rwsem_sleep_writer=310 rwsem_wake_reader=355 rwsem_wake_writer=2335 rwsem_wlock=261 rwsem_wlock_fail=0 rwsem_wtrylock=20583 It can be seen that most of the lock acquisitions in the slowpath were write-locks in the optimistic spinning code path with no sleeping at all. For this system, over 97% of the locks are acquired via optimistic spinning. It illustrates the importance of optimistic spinning in improving the performance of rwsem. Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Davidlohr Bueso <dbueso@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Davidlohr Bueso <dave@stgolabs.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: Tim Chen <tim.c.chen@linux.intel.com> Cc: Will Deacon <will.deacon@arm.com> Link: http://lkml.kernel.org/r/20190404174320.22416-11-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-04 17:43:19 +00:00
LOCK_EVENT(rwsem_rlock) /* # of read locks acquired */
LOCK_EVENT(rwsem_rlock_steal) /* # of read locks by lock stealing */
locking/rwsem: Enable lock event counting Add lock event counting calls so that we can track the number of lock events happening in the rwsem code. With CONFIG_LOCK_EVENT_COUNTS on and booting a 4-socket 112-thread x86-64 system, the rwsem counts after system bootup were as follows: rwsem_opt_fail=261 rwsem_opt_wlock=50636 rwsem_rlock=445 rwsem_rlock_fail=0 rwsem_rlock_fast=22 rwsem_rtrylock=810144 rwsem_sleep_reader=441 rwsem_sleep_writer=310 rwsem_wake_reader=355 rwsem_wake_writer=2335 rwsem_wlock=261 rwsem_wlock_fail=0 rwsem_wtrylock=20583 It can be seen that most of the lock acquisitions in the slowpath were write-locks in the optimistic spinning code path with no sleeping at all. For this system, over 97% of the locks are acquired via optimistic spinning. It illustrates the importance of optimistic spinning in improving the performance of rwsem. Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Davidlohr Bueso <dbueso@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Davidlohr Bueso <dave@stgolabs.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: Tim Chen <tim.c.chen@linux.intel.com> Cc: Will Deacon <will.deacon@arm.com> Link: http://lkml.kernel.org/r/20190404174320.22416-11-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-04 17:43:19 +00:00
LOCK_EVENT(rwsem_rlock_fast) /* # of fast read locks acquired */
LOCK_EVENT(rwsem_rlock_fail) /* # of failed read lock acquisitions */
locking/rwsem: Implement lock handoff to prevent lock starvation Because of writer lock stealing, it is possible that a constant stream of incoming writers will cause a waiting writer or reader to wait indefinitely leading to lock starvation. This patch implements a lock handoff mechanism to disable lock stealing and force lock handoff to the first waiter or waiters (for readers) in the queue after at least a 4ms waiting period unless it is a RT writer task which doesn't need to wait. The waiting period is used to avoid discouraging lock stealing too much to affect performance. The setting and clearing of the handoff bit is serialized by the wait_lock. So racing is not possible. A rwsem microbenchmark was run for 5 seconds on a 2-socket 40-core 80-thread Skylake system with a v5.1 based kernel and 240 write_lock threads with 5us sleep critical section. Before the patch, the min/mean/max numbers of locking operations for the locking threads were 1/7,792/173,696. After the patch, the figures became 5,842/6,542/7,458. It can be seen that the rwsem became much more fair, though there was a drop of about 16% in the mean locking operations done which was a tradeoff of having better fairness. Making the waiter set the handoff bit right after the first wakeup can impact performance especially with a mixed reader/writer workload. With the same microbenchmark with short critical section and equal number of reader and writer threads (40/40), the reader/writer locking operation counts with the current patch were: 40 readers, Iterations Min/Mean/Max = 1,793/1,794/1,796 40 writers, Iterations Min/Mean/Max = 1,793/34,956/86,081 By making waiter set handoff bit immediately after wakeup: 40 readers, Iterations Min/Mean/Max = 43/44/46 40 writers, Iterations Min/Mean/Max = 43/1,263/3,191 Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Will Deacon <will.deacon@arm.com> Cc: huang ying <huang.ying.caritas@gmail.com> Link: https://lkml.kernel.org/r/20190520205918.22251-8-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-05-20 20:59:06 +00:00
LOCK_EVENT(rwsem_rlock_handoff) /* # of read lock handoffs */
locking/rwsem: Enable lock event counting Add lock event counting calls so that we can track the number of lock events happening in the rwsem code. With CONFIG_LOCK_EVENT_COUNTS on and booting a 4-socket 112-thread x86-64 system, the rwsem counts after system bootup were as follows: rwsem_opt_fail=261 rwsem_opt_wlock=50636 rwsem_rlock=445 rwsem_rlock_fail=0 rwsem_rlock_fast=22 rwsem_rtrylock=810144 rwsem_sleep_reader=441 rwsem_sleep_writer=310 rwsem_wake_reader=355 rwsem_wake_writer=2335 rwsem_wlock=261 rwsem_wlock_fail=0 rwsem_wtrylock=20583 It can be seen that most of the lock acquisitions in the slowpath were write-locks in the optimistic spinning code path with no sleeping at all. For this system, over 97% of the locks are acquired via optimistic spinning. It illustrates the importance of optimistic spinning in improving the performance of rwsem. Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Davidlohr Bueso <dbueso@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Davidlohr Bueso <dave@stgolabs.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: Tim Chen <tim.c.chen@linux.intel.com> Cc: Will Deacon <will.deacon@arm.com> Link: http://lkml.kernel.org/r/20190404174320.22416-11-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-04 17:43:19 +00:00
LOCK_EVENT(rwsem_wlock) /* # of write locks acquired */
LOCK_EVENT(rwsem_wlock_fail) /* # of failed write lock acquisitions */
locking/rwsem: Implement lock handoff to prevent lock starvation Because of writer lock stealing, it is possible that a constant stream of incoming writers will cause a waiting writer or reader to wait indefinitely leading to lock starvation. This patch implements a lock handoff mechanism to disable lock stealing and force lock handoff to the first waiter or waiters (for readers) in the queue after at least a 4ms waiting period unless it is a RT writer task which doesn't need to wait. The waiting period is used to avoid discouraging lock stealing too much to affect performance. The setting and clearing of the handoff bit is serialized by the wait_lock. So racing is not possible. A rwsem microbenchmark was run for 5 seconds on a 2-socket 40-core 80-thread Skylake system with a v5.1 based kernel and 240 write_lock threads with 5us sleep critical section. Before the patch, the min/mean/max numbers of locking operations for the locking threads were 1/7,792/173,696. After the patch, the figures became 5,842/6,542/7,458. It can be seen that the rwsem became much more fair, though there was a drop of about 16% in the mean locking operations done which was a tradeoff of having better fairness. Making the waiter set the handoff bit right after the first wakeup can impact performance especially with a mixed reader/writer workload. With the same microbenchmark with short critical section and equal number of reader and writer threads (40/40), the reader/writer locking operation counts with the current patch were: 40 readers, Iterations Min/Mean/Max = 1,793/1,794/1,796 40 writers, Iterations Min/Mean/Max = 1,793/34,956/86,081 By making waiter set handoff bit immediately after wakeup: 40 readers, Iterations Min/Mean/Max = 43/44/46 40 writers, Iterations Min/Mean/Max = 43/1,263/3,191 Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Will Deacon <will.deacon@arm.com> Cc: huang ying <huang.ying.caritas@gmail.com> Link: https://lkml.kernel.org/r/20190520205918.22251-8-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-05-20 20:59:06 +00:00
LOCK_EVENT(rwsem_wlock_handoff) /* # of write lock handoffs */