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Subject: Re: REGRESSION: Performance regressions from switching
 anon_vma->lock to mutex
From: Tim Chen <tim.c.chen@linux.intel.com>
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Date: Wed, 15 Jun 2011 18:08:28 -0700
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andi Kleen <ak@linux.intel.com>, Shaohua Li <shaohua.li@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, Hugh Dickins <hughd@google.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, David Miller <davem@davemloft.net>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Russell King <rmk@arm.linux.org.uk>, Paul Mundt <lethal@linux-sh.org>, Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>, "Luck, Tony" <tony.luck@intel.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Mel Gorman <mel@csn.ul.ie>, Nick Piggin <npiggin@kernel.dk>, Namhyung Kim <namhyung@gmail.com>, "Shi, Alex" <alex.shi@intel.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "Rafael J. Wysocki" <rjw@sisk.pl>

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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