From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Mason <chris.mason@oracle.com>
Subject: Re: [GIT PULL] adaptive spinning mutexes
Date: Wed, 14 Jan 2009 13:40:46 -0500
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Gregory Haskins <ghaskins@novell.com>,
	Matthew Wilcox <matthew@wil.cx>,
	Andi Kleen <andi@firstfloor.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-btrfs <linux-btrfs@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Nick Piggin <npiggin@suse.de>,
	Peter Morreale <pmorreale@novell.com>,
	Sven Dietrich <SDietrich@novell.com>,
	Dmitry Adamushko <dmitry.adamushko@gmail.com>,
	Johannes Weiner <hannes@cmpxchg.org>
To: Ingo Molnar <mingo@elte.hu>
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On Wed, 2009-01-14 at 19:33 +0100, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > Full series, including changelogs available at:
> > 
> >  http://programming.kicks-ass.net/kernel-patches/mutex-adaptive-spin/
> > 
> > and should shortly appear in a git tree near Ingo :-)
> 
> Linus,
> 
> Please pull the adaptive-mutexes-for-linus git tree from:
> 
>    git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git adaptive-mutexes-for-linus
> 

I was going to put this into the btrfs tree, but since you have a branch
just for adaptive mutexes, is it easier to put there?

From: Chris Mason <chris.mason@oracle.com>

Btrfs: stop spinning on mutex_trylock and let the adaptive code spin for us

Mutexes now spin internally and the btrfs spin is no longer required for
performance.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 39bae77..40ba8e8 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -37,16 +37,6 @@
 
 int btrfs_tree_lock(struct extent_buffer *eb)
 {
-	int i;
-
-	if (mutex_trylock(&eb->mutex))
-		return 0;
-	for (i = 0; i < 512; i++) {
-		cpu_relax();
-		if (mutex_trylock(&eb->mutex))
-			return 0;
-	}
-	cpu_relax();
 	mutex_lock_nested(&eb->mutex, BTRFS_MAX_LEVEL - btrfs_header_level(eb));
 	return 0;
 }