locking/mutex: Allow next waiter lockless wakeup

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>

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 89350f924c859f006beb96a6888014387db4a744..79d2d765a75f1fef4945dacd2b0aa07b77eba336 100644 (file)
--- 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 mutex *lock, int nested)
                                           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);
 }
 
 /*