linux-kernel - Re: REGRESSION: Performance regressions from switching anon

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Date:	Thu, 16 Jun 2011 13:26:12 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andi Kleen <ak@...ux.intel.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Russell King <rmk@....linux.org.uk>,
	Paul Mundt <lethal@...ux-sh.org>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	"Luck, Tony" <tony.luck@...el.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Namhyung Kim <namhyung@...il.com>,
	"Shi, Alex" <alex.shi@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: REGRESSION: Performance regressions from switching
 anon_vma->lock to mutex

On Wed, 2011-06-15 at 18:50 -0700, Linus Torvalds wrote:

> 
> Tim, have you tried running your bigger load with that patch? You
> could try my patch on top too just to match Peter's tree, but I doubt
> that's the big first-order issue.
> 
>                        Linus

I ran exim with different kernel versions.  Using 2.6.39-vanilla
kernel as a baseline, the results are as follow:

			Throughput
2.6.39(vanilla)		100.0%
2.6.39+ra-patch 	166.7%  (+66.7%)	(note: tmpfs readahead patchset is merged in 3.0-rc2)
3.0-rc2(vanilla)	 68.0%	(-32%)
3.0-rc2+linus		115.7%	(+15.7%)
3.0-rc2+linus+softirq	 86.2%	(-17.3%)

So Linus' patch certainly helped things over vanilla 3.0-rc2, but throughput is still 
less than the 2.6.39 with the readahead patch set.  The softirq patch I used was from Ingo's
combined patch from Shaohua and Paul.  It seems odd that it makes things worse.  I will
recheck this data probably just this patch and without Linus' patch later.

I also notice that the run to run variations have increased quite a bit for 3.0-rc2.
I'm using 6 runs per kernel.  Perhaps a side effect of converting the anon_vma->lock to mutex?

			(Max-Min)/avg 
2.6.39(vanilla)		3%
2.6.39+ra-patch 	3%	
3.0-rc2(vanilla)	20% 
3.0-rc2+linus		36%
3.0-rc2+linus+softirq	40% 

Thanks.

Tim

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