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Date: Wed, 15 Jun 2011 13:57:29 -0700
From: Andi Kleen <ak@linux.intel.com>
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Subject: Re: REGRESSION: Performance regressions from switching anon_vma->lock
 to mutex
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tim Chen <tim.c.chen@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>


>       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.

-Andi



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