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locking/percpu-rwsem: Move __this_cpu_inc() into the slowpath 

As preparation to rework __percpu_down_read() move the
__this_cpu_inc() into it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200131151540.041600199@infradead.org
This commit is contained in:
Peter Zijlstra 2019-10-30 20:17:51 +01:00 committed by Ingo Molnar
parent 206c98ffbe
commit 71365d4023
2 changed files with 8 additions and 4 deletions
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10
include/linux/percpu-rwsem.h
View File

@ -59,8 +59,9 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
* and that once the synchronize_rcu() is done, the writer will see
* anything we did within this RCU-sched read-size critical section.
*/
__this_cpu_inc(*sem->read_count);
if (unlikely(!rcu_sync_is_idle(&sem->rss)))
if (likely(rcu_sync_is_idle(&sem->rss)))
__this_cpu_inc(*sem->read_count);
else
__percpu_down_read(sem, false); /* Unconditional memory barrier */
/*
* The preempt_enable() prevents the compiler from
@ -77,8 +78,9 @@ static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
/*
* Same as in percpu_down_read().
*/
__this_cpu_inc(*sem->read_count);
if (unlikely(!rcu_sync_is_idle(&sem->rss)))
if (likely(rcu_sync_is_idle(&sem->rss)))
__this_cpu_inc(*sem->read_count);
else
ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
preempt_enable();
/*

2
kernel/locking/percpu-rwsem.c
View File

@ -47,6 +47,8 @@ EXPORT_SYMBOL_GPL(percpu_free_rwsem);
bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
{
__this_cpu_inc(*sem->read_count);
/*
* Due to having preemption disabled the decrement happens on
* the same CPU as the increment, avoiding the