This is a note to let you know that I've just added the patch titled
locking/mutex: Allow next waiter lockless wakeup
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
locking-mutex-allow-next-waiter-lockless-wakeup.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1329ce6fbbe4536592dfcfc8d64d61bfeb598fe6 Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Date: Sun, 24 Jan 2016 18:23:43 -0800
Subject: locking/mutex: Allow next waiter lockless wakeup
From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
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@xxxxxxx>
Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Ding Tianhong <dingtianhong@xxxxxxxxxx>
Cc: Jason Low <jason.low2@xxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Waiman Long <waiman.long@xxxxxxx>
Cc: Will Deacon <Will.Deacon@xxxxxxx>
Link: http://lkml.kernel.org/r/20160125022343.GA3322@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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);
}
/*
Patches currently in stable-queue which might be from dave@xxxxxxxxxxxx are
queue-4.4/locking-mutex-allow-next-waiter-lockless-wakeup.patch
queue-4.4/futex-replace-barrier-in-unqueue_me-with-read_once.patch