From 1bf11c53535ab87e3bf14ecdf6747bf46f601c5d Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Mon, 22 Oct 2012 19:39:16 -0400 Subject: [PATCH] percpu-rw-semaphores: use rcu_read_lock_sched Use rcu_read_lock_sched / rcu_read_unlock_sched / synchronize_sched instead of rcu_read_lock / rcu_read_unlock / synchronize_rcu. This is an optimization. The RCU-protected region is very small, so there will be no latency problems if we disable preempt in this region. So we use rcu_read_lock_sched / rcu_read_unlock_sched that translates to preempt_disable / preempt_disable. It is smaller (and supposedly faster) than preemptible rcu_read_lock / rcu_read_unlock. Signed-off-by: Mikulas Patocka Signed-off-by: Linus Torvalds --- include/linux/percpu-rwsem.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h index 18f35b54286c..250a4acddb2b 100644 --- a/include/linux/percpu-rwsem.h +++ b/include/linux/percpu-rwsem.h @@ -17,16 +17,16 @@ struct percpu_rw_semaphore { static inline void percpu_down_read(struct percpu_rw_semaphore *p) { - rcu_read_lock(); + rcu_read_lock_sched(); if (unlikely(p->locked)) { - rcu_read_unlock(); + rcu_read_unlock_sched(); mutex_lock(&p->mtx); this_cpu_inc(*p->counters); mutex_unlock(&p->mtx); return; } this_cpu_inc(*p->counters); - rcu_read_unlock(); + rcu_read_unlock_sched(); light_mb(); /* A, between read of p->locked and read of data, paired with D */ } @@ -51,7 +51,7 @@ static inline void percpu_down_write(struct percpu_rw_semaphore *p) { mutex_lock(&p->mtx); p->locked = true; - synchronize_rcu(); + synchronize_sched(); /* make sure that all readers exit the rcu_read_lock_sched region */ while (__percpu_count(p->counters)) msleep(1); heavy_mb(); /* C, between read of p->counter and write to data, paired with B */ -- 2.20.1