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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 14:12:16 -0700
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To: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, 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 13:57 -0700, Andi Kleen wrote:
> >       7.44%        exim  [kernel.kallsyms]              [k] format_decode
> >                    |
> >                    --- format_decod
> 
> 
> This is a glibc issue. exim calls libdb and libdb asks sysconf for the 
> number of CPUs to tune
> its locking, and glibc reads /proc/stat.  And /proc/stat is incredible slow.
> 
> I would blame glibc, but in this case it's really the kernel to blame 
> for not providing proper
> interface.
> 
> This was my motivation for the sysconf() syscall I submitted some time ago.
> https://lkml.org/lkml/2011/5/13/455
> 
> Anyways a quick workaround is to use this LD_PRELOAD: 
> http://halobates.de/smallsrc/sysconf.c
> But it's not 100% equivalent.
> 

Thanks to Andi for providing the info.  We've used this workaround in
our testing so it will not mask true kernel scaling bottlenecks.

Tim

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