linux/kernel/locking
Wanpeng Li 89340d0935 Revert "locking/pvqspinlock: Don't wait if vCPU is preempted"
This patch reverts commit 75437bb304 (locking/pvqspinlock: Don't
wait if vCPU is preempted).  A large performance regression was caused
by this commit.  on over-subscription scenarios.

The test was run on a Xeon Skylake box, 2 sockets, 40 cores, 80 threads,
with three VMs of 80 vCPUs each.  The score of ebizzy -M is reduced from
13000-14000 records/s to 1700-1800 records/s:

          Host                Guest                score

vanilla w/o kvm optimizations     upstream    1700-1800 records/s
vanilla w/o kvm optimizations     revert      13000-14000 records/s
vanilla w/ kvm optimizations      upstream    4500-5000 records/s
vanilla w/ kvm optimizations      revert      14000-15500 records/s

Exit from aggressive wait-early mechanism can result in premature yield
and extra scheduling latency.

Actually, only 6% of wait_early events are caused by vcpu_is_preempted()
being true.  However, when one vCPU voluntarily releases its vCPU, all
the subsequently waiters in the queue will do the same and the cascading
effect leads to bad performance.

kvm optimizations:
[1] commit d73eb57b80 (KVM: Boost vCPUs that are delivering interrupts)
[2] commit 266e85a5ec (KVM: X86: Boost queue head vCPU to mitigate lock waiter preemption)

Tested-by: loobinliu@tencent.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: loobinliu@tencent.com
Cc: stable@vger.kernel.org
Fixes: 75437bb304 (locking/pvqspinlock: Don't wait if vCPU is preempted)
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2019-09-25 10:22:37 +02:00
..
Makefile locking/rwsem: Merge rwsem.h and rwsem-xadd.c into rwsem.c 2019-06-17 12:27:57 +02:00
lock_events.c locking/lock_events: Don't show pvqspinlock events on bare metal 2019-04-10 10:56:05 +02:00
lock_events.h locking/lock_events: Use raw_cpu_{add,inc}() for stats 2019-06-03 12:32:56 +02:00
lock_events_list.h locking/rwsem: Adaptive disabling of reader optimistic spinning 2019-06-17 12:28:09 +02:00
lockdep.c Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-09-16 16:49:55 -07:00
lockdep_internals.h locking/lockdep: Report more stack trace statistics 2019-07-25 15:43:28 +02:00
lockdep_proc.c locking/lockdep: Report more stack trace statistics 2019-07-25 15:43:28 +02:00
lockdep_states.h locking/lockdep: Rework FS_RECLAIM annotation 2017-08-10 12:29:03 +02:00
locktorture.c torture: Allow inter-stutter interval to be specified 2019-05-28 09:06:09 -07:00
mcs_spinlock.h locking/mcs: Use smp_cond_load_acquire() in MCS spin loop 2018-04-27 09:48:49 +02:00
mutex-debug.c locking/mutex: Replace spin_is_locked() with lockdep 2018-11-12 09:06:22 -08:00
mutex-debug.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mutex.c mutex: Fix up mutex_waiter usage 2019-08-08 09:09:25 +02:00
mutex.h mutex: Fix up mutex_waiter usage 2019-08-08 09:09:25 +02:00
osq_lock.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
percpu-rwsem.c Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu 2019-06-28 19:46:47 +02:00
qrwlock.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
qspinlock.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
qspinlock_paravirt.h Revert "locking/pvqspinlock: Don't wait if vCPU is preempted" 2019-09-25 10:22:37 +02:00
qspinlock_stat.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
rtmutex-debug.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rtmutex-debug.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rtmutex.c sched/core: Convert get_task_struct() to return the task 2019-07-25 15:51:54 +02:00
rtmutex.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rtmutex_common.h locking/rtmutex: Handle non enqueued waiters gracefully in remove_waiter() 2018-03-28 23:01:30 +02:00
rwsem.c locking/rwsem: Check for operations on an uninitialized rwsem 2019-08-06 12:49:15 +02:00
rwsem.h locking/rwsem: Merge rwsem.h and rwsem-xadd.c into rwsem.c 2019-06-17 12:27:57 +02:00
semaphore.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 436 2019-06-05 17:37:17 +02:00
spinlock.c asm-generic/mmiowb: Add generic implementation of mmiowb() tracking 2019-04-08 11:59:39 +01:00
spinlock_debug.c mmiowb: Hook up mmiowb helpers to spinlocks and generic I/O accessors 2019-04-08 11:59:47 +01:00
test-ww_mutex.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 9 2019-05-21 11:28:40 +02:00