From 71365d40232110f7b029befc9033ea311d680611 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 30 Oct 2019 20:17:51 +0100 Subject: [PATCH] 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) Signed-off-by: Ingo Molnar Reviewed-by: Davidlohr Bueso Acked-by: Will Deacon Acked-by: Waiman Long Tested-by: Juri Lelli Link: https://lkml.kernel.org/r/20200131151540.041600199@infradead.org --- include/linux/percpu-rwsem.h | 10 ++++++---- kernel/locking/percpu-rwsem.c | 2 ++ 2 files changed, 8 insertions(+), 4 deletions(-) diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h index 4ceaa19..bb5b71c 100644 --- a/include/linux/percpu-rwsem.h +++ b/include/linux/percpu-rwsem.h @@ -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(); /* diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c index 969389d..becf925 100644 --- a/kernel/locking/percpu-rwsem.c +++ b/kernel/locking/percpu-rwsem.c @@ -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 -- 2.7.4