Commit-ID: 72d5305dcb3637913c2c37e847a4de9028e49244 Gitweb: http://git.kernel.org/tip/72d5305dcb3637913c2c37e847a4de9028e49244 Author: Jason Low <jason.low2@xxxxxx> AuthorDate: Wed, 11 Jun 2014 11:37:23 -0700 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Sat, 5 Jul 2014 11:25:42 +0200 locking/mutexes: Optimize mutex trylock slowpath The mutex_trylock() function calls into __mutex_trylock_fastpath() when trying to obtain the mutex. On 32 bit x86, in the !__HAVE_ARCH_CMPXCHG case, __mutex_trylock_fastpath() calls directly into __mutex_trylock_slowpath() regardless of whether or not the mutex is locked. In __mutex_trylock_slowpath(), we then acquire the wait_lock spinlock, xchg() lock->count with -1, then set lock->count back to 0 if there are no waiters, and return true if the prev lock count was 1. However, if the mutex is already locked, then there isn't much point in attempting all of the above expensive operations. In this patch, we only attempt the above trylock operations if the mutex is unlocked. Signed-off-by: Jason Low <jason.low2@xxxxxx> Reviewed-by: Davidlohr Bueso <davidlohr@xxxxxx> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: akpm@xxxxxxxxxxxxxxxxxxxx Cc: tim.c.chen@xxxxxxxxxxxxxxx Cc: paulmck@xxxxxxxxxxxxxxxxxx Cc: rostedt@xxxxxxxxxxx Cc: Waiman.Long@xxxxxx Cc: scott.norton@xxxxxx Cc: aswin@xxxxxx Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/1402511843-4721-5-git-send-email-jason.low2@xxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- kernel/locking/mutex.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index e4d997b..11b103d 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -820,6 +820,10 @@ static inline int __mutex_trylock_slowpath(atomic_t *lock_count) unsigned long flags; int prev; + /* No need to trylock if the mutex is locked. */ + if (mutex_is_locked(lock)) + return 0; + spin_lock_mutex(&lock->wait_lock, flags); prev = atomic_xchg(&lock->count, -1); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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