Commit-ID: 1d8fe7dc8078b23e060ec62ccb4cdc1ac3c41bf8 Gitweb: http://git.kernel.org/tip/1d8fe7dc8078b23e060ec62ccb4cdc1ac3c41bf8 Author: Jason Low <jason.l...@hp.com> AuthorDate: Tue, 28 Jan 2014 11:13:14 -0800 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Tue, 11 Mar 2014 12:14:54 +0100
locking/mutexes: Unlock the mutex without the wait_lock When running workloads that have high contention in mutexes on an 8 socket machine, mutex spinners would often spin for a long time with no lock owner. The main reason why this is occuring is in __mutex_unlock_common_slowpath(), if __mutex_slowpath_needs_to_unlock(), then the owner needs to acquire the mutex->wait_lock before releasing the mutex (setting lock->count to 1). When the wait_lock is contended, this delays the mutex from being released. We should be able to release the mutex without holding the wait_lock. Signed-off-by: Jason Low <jason.l...@hp.com> Cc: chegu_vi...@hp.com Cc: paul...@linux.vnet.ibm.com Cc: waiman.l...@hp.com Cc: torva...@linux-foundation.org Cc: t...@linutronix.de Cc: r...@redhat.com Cc: a...@linux-foundation.org Cc: davidl...@hp.com Cc: h...@zytor.com Cc: a...@firstfloor.org Cc: as...@hp.com Cc: scott.nor...@hp.com Signed-off-by: Peter Zijlstra <pet...@infradead.org> Link: http://lkml.kernel.org/r/1390936396-3962-4-git-send-email-jason.l...@hp.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/locking/mutex.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 82dad2c..dc3d6f2 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -671,10 +671,6 @@ __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) struct mutex *lock = container_of(lock_count, struct mutex, count); unsigned long flags; - spin_lock_mutex(&lock->wait_lock, flags); - mutex_release(&lock->dep_map, nested, _RET_IP_); - debug_mutex_unlock(lock); - /* * some architectures leave the lock unlocked in the fastpath failure * case, others need to leave it locked. In the later case we have to @@ -683,6 +679,10 @@ __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) if (__mutex_slowpath_needs_to_unlock()) atomic_set(&lock->count, 1); + spin_lock_mutex(&lock->wait_lock, flags); + mutex_release(&lock->dep_map, nested, _RET_IP_); + debug_mutex_unlock(lock); + if (!list_empty(&lock->wait_list)) { /* get the first entry from the wait-list: */ struct mutex_waiter *waiter = -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
