linux-kernel - Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

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Date:	Fri, 09 Jan 2009 19:16:04 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Mason <chris.mason@...cle.com>,
	Ingo Molnar <mingo@...e.hu>, paulmck@...ux.vnet.ibm.com,
	Gregory Haskins <ghaskins@...ell.com>,
	Matthew Wilcox <matthew@....cx>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>
Subject: Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

On Fri, 2009-01-09 at 11:44 -0500, Steven Rostedt wrote:

> When we get to the schedule() it then needs to be a:
> 
> 	preempt_enable_no_resched();
> 	schedule();

On that note:

Index: linux-2.6/kernel/mutex.c
===================================================================
--- linux-2.6.orig/kernel/mutex.c
+++ linux-2.6/kernel/mutex.c
@@ -220,7 +220,9 @@ __mutex_lock_common(struct mutex *lock, 
 		__set_task_state(task, state);
 
 		/* didnt get the lock, go to sleep: */
+		preempt_disable();
 		spin_unlock_mutex(&lock->wait_lock, flags);
+		preempt_enable_no_resched();
 		schedule();
 		spin_lock_mutex(&lock->wait_lock, flags);
 	}


actually improves mutex performance on PREEMPT=y
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