Messages in this thread Patch in this message | | | From | Jason Low <> | Subject | [PATCH v2 3/5] mutex: Unlock the mutex without the wait_lock | Date | Tue, 28 Jan 2014 11:13:14 -0800 |
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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.low2@hp.com> --- kernel/locking/mutex.c | 8 ++++---- 1 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 7519d27..6d85b08 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -718,10 +718,6 @@ __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 @@ -730,6 +726,10 @@ __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 = -- 1.7.1
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