linux-kernel - Re: [GIT PULL] adaptive spinning mutexes

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Date:	Thu, 15 Jan 2009 19:06:19 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Gregory Haskins <ghaskins@...ell.com>,
	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>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [GIT PULL] adaptive spinning mutexes


* Matthew Wilcox <matthew@....cx> wrote:

> On Wed, Jan 14, 2009 at 08:28:11PM +0100, Ingo Molnar wrote:
> >                       [v2.6.14]     [v2.6.29]
> > 
> >                       Semaphores  | Mutexes
> >             ----------------------------------------------
> >                                   | no-spin           spin
> >                                   |
> >   [tmpfs]   ops/sec:       50713  |  291038         392865       (+34.9%)
> >   [ext3]    ops/sec:       45214  |  283291         435674       (+53.7%)
> > 
> > A 10x macro-performance improvement on ext3, compared to 2.6.14 :-)
> > 
> > While lots of other details got changed meanwhile, i'm sure most of 
> > the performance win on this particular VFS workload comes from 
> > mutexes.
> 
> I asked a couple of our benchmarking teams to try -v9.  Neither the OLTP 
> benchmark, nor the kernel-perf test suite found any significant 
> performance change.  I suspect mutex contention isn't a significant 
> problem for most workloads.

basically only VFS is mutex-bound really, and few of the 'benchmarks' tend 
to be VFS intense. Maybe things like mail-server benchmarks would do that.

Also, -v9 is like two days old code ;-) Old and crufty. The real 
performance uptick was not even in -v10 but in -v11 (the one we submitted 
in this thread).

	Ingo
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