diff options
| author | Peter Zijlstra | 2016-06-01 20:58:15 +0200 |
|---|---|---|
| committer | Ingo Molnar | 2016-06-08 15:17:01 +0200 |
| commit | 6428671bae97caa7040e24e79e969fd87908f4f3 (patch) | |
| tree | 67549d91213b5fc3bb48a243ebfaf1ef3fc2b9a2 /arch/ia64 | |
| parent | ddd0fa73c2b71c35de4fe7ae60a5f1a6cddc2cf0 (diff) | |
locking/mutex: Optimize mutex_trylock() fast-path
A while back Viro posted a number of 'interesting' mutex_is_locked()
users on IRC, one of those was RCU.
RCU seems to use mutex_is_locked() to avoid doing mutex_trylock(), the
regular load before modify pattern.
While the use isn't wrong per se, its curious in that its needed at all,
mutex_trylock() should be good enough on its own to avoid the pointless
cacheline bounces.
So fix those and remove the mutex_is_locked() (ab)use from RCU.
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paul McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <Waiman.Long@hpe.com>
Link: http://lkml.kernel.org/r/20160601185815.GW3190@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/ia64')
| -rw-r--r-- | arch/ia64/include/asm/mutex.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/ia64/include/asm/mutex.h b/arch/ia64/include/asm/mutex.h index f41e66d65e31..28cb819e0ff9 100644 --- a/arch/ia64/include/asm/mutex.h +++ b/arch/ia64/include/asm/mutex.h @@ -82,7 +82,7 @@ __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *)) static inline int __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) { - if (cmpxchg_acq(count, 1, 0) == 1) + if (atomic_read(count) == 1 && cmpxchg_acq(count, 1, 0) == 1) return 1; return 0; } |