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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 <mpatocka@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mikulas Patocka 2012-10-22 19:39:16 -04:00 committed by Linus Torvalds
parent 5c1eabe685
commit 1bf11c5353
1 changed files with 4 additions and 4 deletions
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8
include/linux/percpu-rwsem.h
View File

@ -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 */