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

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Message-ID: <1308186508.17300.423.camel@schen9-DESK>
Date:	Wed, 15 Jun 2011 18:08:28 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andi Kleen <ak@...ux.intel.com>, Shaohua Li <shaohua.li@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...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 23:37 +0200, Peter Zijlstra wrote:
> On Wed, 2011-06-15 at 14:12 -0700, Tim Chen wrote:
> > Thanks to Andi for providing the info.  We've used this workaround in
> > our testing so it will not mask true kernel scaling bottlenecks.
> 
> 
> http://programming.kicks-ass.net/sekrit/39-2.txt.bz2
> http://programming.kicks-ass.net/sekrit/tip-2.txt.bz2
> 
> tip+sirq+linus is still slightly faster than .39 here, although removing
> that sysconf() wreckage closed the gap considerably (needing to know the
> number of cpus to optimize locking sounds like a trainwreck all of its
> own, needing it _that_ often instead of just once at startup is even
> worse).
> 

Peter,

Fengguang's readahead fixes for tmpfs removed another bottleneck before
anon_vma->lock become dominant. https://lkml.org/lkml/2011/4/26/143)
We've found this issue when we were testing exim earlier.
It was merged in 3.0-rc2 but not in plain 2.6.39.  So with this patch on
2.6.39 we should get better comparison with 3.0-rc2.

Thanks.

Tim  


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