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rcu: Move __rcu_read_unlock()'s barrier() within if-statement

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We only need to constrain the compiler if we are actually exiting
the top-level RCU read-side critical section.  This commit therefore
moves the first barrier() cal in __rcu_read_unlock() to inside the
"if" statement, thus avoiding needless register flushes for inner
rcu_read_unlock() calls.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2011-08-01 06:22:11 -07:00 committed by Paul E. McKenney
parent 6846c0c540
commit 6206ab9bab
2 changed files with 3 additions and 13 deletions
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14
include/linux/rcupdate.h
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@ -134,16 +134,6 @@ extern void call_rcu_sched(struct rcu_head *head,
extern void synchronize_sched(void); extern void synchronize_sched(void);
static inline void __rcu_read_lock_bh(void)
{
local_bh_disable();
}
static inline void __rcu_read_unlock_bh(void)
{
local_bh_enable();
}
#ifdef CONFIG_PREEMPT_RCU #ifdef CONFIG_PREEMPT_RCU
extern void __rcu_read_lock(void); extern void __rcu_read_lock(void);
@ -686,7 +676,7 @@ static inline void rcu_read_unlock(void)
*/ */
static inline void rcu_read_lock_bh(void) static inline void rcu_read_lock_bh(void)
{ {
__rcu_read_lock_bh(); local_bh_disable();
__acquire(RCU_BH); __acquire(RCU_BH);
rcu_read_acquire_bh(); rcu_read_acquire_bh();
} }
@ -700,7 +690,7 @@ static inline void rcu_read_unlock_bh(void)
{ {
rcu_read_release_bh(); rcu_read_release_bh();
__release(RCU_BH); __release(RCU_BH);
__rcu_read_unlock_bh(); local_bh_enable();
} }
/** /**

2
kernel/rcutree_plugin.h
View File

@ -415,10 +415,10 @@ void __rcu_read_unlock(void)
{ {
struct task_struct *t = current; struct task_struct *t = current;
barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */
if (t->rcu_read_lock_nesting != 1) if (t->rcu_read_lock_nesting != 1)
--t->rcu_read_lock_nesting; --t->rcu_read_lock_nesting;
else { else {
barrier(); /* critical section before exit code. */
t->rcu_read_lock_nesting = INT_MIN; t->rcu_read_lock_nesting = INT_MIN;
barrier(); /* assign before ->rcu_read_unlock_special load */ barrier(); /* assign before ->rcu_read_unlock_special load */
if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))