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Waiman Long 4f23dbc1e6 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>
 		2019-06-17 12:27:59 +02:00
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bpf treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 363 2019-06-05 17:37:09 +02:00
cgroup Merge branch 'for-5.2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2019-06-14 17:46:14 -10:00
configs kvm_config: add CONFIG_VIRTIO_MENU 2018-10-24 20:55:56 -04:00
debug treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
dma treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 333 2019-06-05 17:37:06 +02:00
events perf/ring-buffer: Use regular variables for nesting 2019-05-24 09:00:11 +02:00
gcov treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
irq treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
livepatch This includes the following fixes: 2019-06-15 07:24:11 -10:00
locking locking/rwsem: Implement lock handoff to prevent lock starvation 2019-06-17 12:27:59 +02:00
power SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
printk treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
rcu treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
sched treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
time timekeeping: Repair ktime_get_coarse*() granularity 2019-06-14 11:51:44 +02:00
trace This includes the following fixes: 2019-06-15 07:24:11 -10:00
.gitignore Provide in-kernel headers to make extending kernel easier 2019-04-29 16:48:03 +02:00
Kconfig.freezer treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.hz treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.locks treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.preempt treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Makefile kheaders: Move from proc to sysfs 2019-05-24 20:16:01 +02:00
acct.c acct_on(): don't mess with freeze protection 2019-04-04 21:04:13 -04:00
async.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
audit.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
audit.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
audit_fsnotify.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
audit_tree.c fsnotify: switch send_to_group() and ->handle_event to const struct qstr * 2019-04-26 13:51:03 -04:00
audit_watch.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
auditfilter.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
auditsc.c Merge branch 'work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-05-07 20:03:32 -07:00
backtracetest.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
bounds.c kbuild: fix kernel/bounds.c 'W=1' warning 2018-10-31 08:54:14 -07:00
capability.c LSM: add SafeSetID module that gates setid calls 2019-01-25 11:22:43 -08:00
compat.c kernel/compat.c: mark expected switch fall-throughs 2019-05-15 08:16:14 -07:00
configs.c kernel/configs: use .incbin directive to embed config_data.gz 2019-03-07 18:32:02 -08:00
context_tracking.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
cpu.c x86/power: Fix 'nosmt' vs hibernation triple fault during resume 2019-06-03 12:02:03 +02:00
cpu_pm.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 282 2019-06-05 17:36:37 +02:00
crash_core.c kexec: export PG_offline to VMCOREINFO 2019-03-05 21:07:14 -08:00
crash_dump.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
cred.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2019-06-11 15:44:45 -10:00
delayacct.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 25 2019-05-21 11:52:39 +02:00
dma.c
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elfcore.c
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exec_domain.c
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exit.c cgroup: Call cgroup_release() before __exit_signal() 2019-05-31 10:38:57 -07:00
extable.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
fail_function.c treewide: Switch printk users from %pf and %pF to %ps and %pS, respectively 2019-04-09 14:19:06 +02:00
fork.c locking/lockdep: Use lockdep_init_task for task initiation consistently 2019-06-03 11:55:42 +02:00
freezer.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
futex.c Linux 5.2-rc3 2019-06-03 11:50:18 +02:00
gen_kheaders.sh kheaders: Do not regenerate archive if config is not changed 2019-05-24 20:16:01 +02:00
groups.c
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hung_task.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
iomem.c mm/resource: Use resource_overlaps() to simplify region_intersects() 2019-04-19 12:59:36 +02:00
irq_work.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
jump_label.c jump_label: Batch updates if arch supports it 2019-06-17 12:09:22 +02:00
kallsyms.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
kcmp.c
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kcov.c kcov: convert kcov.refcount to refcount_t 2019-03-07 18:32:02 -08:00
kexec.c
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kexec_core.c power/suspend: Add function to disable secondaries for suspend 2019-05-03 19:42:41 +02:00
kexec_file.c mm: memblock: make keeping memblock memory opt-in rather than opt-out 2019-05-14 09:47:50 -07:00
kexec_internal.h
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kheaders.c kheaders: Move from proc to sysfs 2019-05-24 20:16:01 +02:00
kmod.c
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kprobes.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
ksysfs.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 170 2019-05-30 11:26:39 -07:00
kthread.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
latencytop.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
memremap.c mm/devm_memremap_pages: fix final page put race 2019-06-13 17:34:56 -10:00
module-internal.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
module.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
module_signing.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
notifier.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
nsproxy.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
padata.c padata: Replace padata_attr_type default_attrs field with groups 2019-04-25 22:06:11 +02:00
panic.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
params.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
pid.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
pid_namespace.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
profile.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
ptrace.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2019-06-11 15:44:45 -10:00
range.c
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reboot.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
relay.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-03-12 13:27:20 -07:00
resource.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
rseq.c rseq: Remove superfluous rseq_len from task_struct 2019-04-19 12:39:32 +02:00
seccomp.c audit/stable-5.2 PR 20190507 2019-05-07 19:06:04 -07:00
signal.c signal: improve comments 2019-06-05 15:06:07 +02:00
smp.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
smpboot.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
smpboot.h
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softirq.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 430 2019-06-05 17:37:16 +02:00
stackleak.c stackleak: Mark stackleak_track_stack() as notrace 2018-12-05 19:31:44 -08:00
stacktrace.c Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-06-02 11:04:42 -07:00
stop_machine.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 38 2019-05-24 17:27:11 +02:00
sys.c prctl_set_mm: downgrade mmap_sem to read lock 2019-06-01 15:51:31 -07:00
sys_ni.c signal: support CLONE_PIDFD with pidfd_send_signal 2019-05-07 14:31:03 +02:00
sysctl.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
sysctl_binary.c kernel/sysctl: add panic_print into sysctl 2019-01-04 13:13:47 -08:00
task_work.c
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taskstats.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
test_kprobes.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 25 2019-05-21 11:52:39 +02:00
torture.c torture: Don't try to offline the last CPU 2019-03-26 14:42:53 -07:00
tracepoint.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
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ucount.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
uid16.c
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user-return-notifier.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
user.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
user_namespace.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
utsname.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
utsname_sysctl.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
watchdog.c watchdog: Fix typo in comment 2019-04-18 14:05:51 +02:00
watchdog_hld.c kernel/watchdog_hld.c: hard lockup message should end with a newline 2019-04-19 09:46:05 -07:00
workqueue.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
workqueue_internal.h sched/core, workqueues: Distangle worker accounting from rq lock 2019-04-16 16:55:15 +02:00