linux-kernel - [GIT PULL] core fixes

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Date:	Tue, 24 Aug 2010 21:01:21 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [GIT PULL] core fixes


Linus,

Please pull the latest core-fixes-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git core-fixes-for-linus

This contains the mutex optimistic spinning fix from Tim Chen. It is not 
a regression fix per se - but the improvement is significant enough (and 
the patch is simple enough as well) to not let this sit for yet another 
cycle.

 Thanks,

	Ingo

------------------>
Tim Chen (1):
      mutex: Improve the scalability of optimistic spinning


 kernel/sched.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 41541d7..09b574e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3865,8 +3865,16 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
 		/*
 		 * Owner changed, break to re-assess state.
 		 */
-		if (lock->owner != owner)
+		if (lock->owner != owner) {
+			/*
+			 * If the lock has switched to a different owner,
+			 * we likely have heavy contention. Return 0 to quit
+			 * optimistic spinning and not contend further:
+			 */
+			if (lock->owner)
+				return 0;
 			break;
+		}
 
 		/*
 		 * Is that owner really running on that cpu?
--
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