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authorMikulas Patocka <mpatocka@redhat.com>2012-10-22 19:39:16 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-28 10:59:36 -0700
commit1bf11c53535ab87e3bf14ecdf6747bf46f601c5d (patch)
tree9170fa956be0f564b988a88685eb82584347c2cf
parent5c1eabe68501d1e1b1586c7f4c46cc531828c4ab (diff)
downloadlinux-1bf11c53535ab87e3bf14ecdf6747bf46f601c5d.tar.bz2
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>
-rw-r--r--include/linux/percpu-rwsem.h8
1 files 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 */