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

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Date:	Wed, 14 Jan 2009 20:28:11 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	"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>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [GIT PULL] adaptive spinning mutexes


* Ingo Molnar <mingo@...e.hu> wrote:

> Latest performance figures, on a 2-socket 16-way Nehalem test-system, 
> running the code above, measured via "test-mutex V 128 10" VFS 
> creat+unlink scalability test on tmpfs and ext3:
> 
>                               no-spin           spin
> 
>  [tmpfs]    avg ops/sec:       291038         392865       (+34.9%)
>  [ext3]     avg ops/sec:       283291         435674       (+53.7%)

Btw., for historic kicks i just went back to v2.6.15-2019-gf17578d - the 
last pre-mutexes semaphore based kernel, using the same .config.

I tracked down two bugs in it to make it boot on a Nehalem, so we can now 
compare the above numbers against historic semaphore performance:

                      [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.

So i think the long mutex migration pain was definitely worth it.

	Ingo
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