4.4-stable review patch. If anyone has any objections, please let me know.
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From: Davidlohr Bueso dave@stgolabs.net
commit 1329ce6fbbe4536592dfcfc8d64d61bfeb598fe6 upstream.
Make use of wake-queues and enable the wakeup to occur after releasing the wait_lock. This is similar to what we do with rtmutex top waiter, slightly shortening the critical region and allow other waiters to acquire the wait_lock sooner. In low contention cases it can also help the recently woken waiter to find the wait_lock available (fastpath) when it continues execution.
Reviewed-by: Waiman Long Waiman.Long@hpe.com Signed-off-by: Davidlohr Bueso dbueso@suse.de Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Ding Tianhong dingtianhong@huawei.com Cc: Jason Low jason.low2@hp.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Paul E. McKenney paulmck@linux.vnet.ibm.com Cc: Paul E. McKenney paulmck@us.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Waiman Long waiman.long@hpe.com Cc: Will Deacon Will.Deacon@arm.com Link: http://lkml.kernel.org/r/20160125022343.GA3322@linux-uzut.site Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/locking/mutex.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -719,6 +719,7 @@ static inline void __mutex_unlock_common_slowpath(struct mutex *lock, int nested) { unsigned long flags; + WAKE_Q(wake_q);
/* * As a performance measurement, release the lock before doing other @@ -746,11 +747,11 @@ __mutex_unlock_common_slowpath(struct mu struct mutex_waiter, list);
debug_mutex_wake_waiter(lock, waiter); - - wake_up_process(waiter->task); + wake_q_add(&wake_q, waiter->task); }
spin_unlock_mutex(&lock->wait_lock, flags); + wake_up_q(&wake_q); }
/*