Commit 1329ce6f authored Jan 24, 2016 by Davidlohr Bueso Committed by Ingo Molnar Feb 29, 2016

locking/mutex: Allow next waiter lockless wakeup



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>

parent 32d62510

kernel/locking/mutex.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -716,6 +716,7 @@ 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
		@@ -743,11 +744,11 @@ __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);
		}

		/*

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