linux-kernel - Re: [PATCH -v8][RFC] mutex: implement adaptive spinning

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Date:	Mon, 12 Jan 2009 18:16:21 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Gregory Haskins <ghaskins@...ell.com>,
	Matthew Wilcox <matthew@....cx>,
	Andi Kleen <andi@...stfloor.org>,
	Chris Mason <chris.mason@...cle.com>,
	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>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [PATCH -v8][RFC] mutex: implement adaptive spinning

On Mon, 2009-01-12 at 08:20 -0800, Linus Torvalds wrote:
> 
> On Mon, 12 Jan 2009, Linus Torvalds wrote:
> > 
> > You made it back into the locked version.
> 
> Btw, even if you probably had some reason for this, one thing to note is 
> that I think Chris' performance testing showed that the version using a 
> lock was inferior to his local btrfs hack, while the unlocked version 
> actually beat his hack.
> 
> Maybe I misunderstood his numbers, though. But if I followed that sub-part 
> of the test right, it really means that the locked version is pointless - 
> it will never be able to replace peoples local hacks for this same thing, 
> because it just doesn't give the performance people are looking for.
> 
> Since the whole (and _only_) point of this thing is to perform well, 
> that's a big deal.

Like said in reply to Chris' email, I just wanted to see if fairness was
worth the effort, because the pure unlocked spin showed significant
unfairness (and I know some people really care about some level of
fairness).

Initial testing with the simple test-mutex thing didn't show too bad
numbers.

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