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Subject: Re: REGRESSION: Performance regressions from switching anon_vma->lock to mutex
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 15 Jun 2011 14:51:34 -0700
Message-ID: <87ea4bd7-8b16-4b24-8fcb-d8e9b6f421ec@email.android.com>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>, Tim Chen <tim.c.chen@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>, Shaohua Li <shaohua.li@intel.com>, Andrew Morton <akpm@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>



Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
>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).

Yeah, I think it's ridiculous to say that glibc is not doing something stupid and that it's a problem with kernel interfaces.

Do the proc file parsing once and cache the result in a static variable. Doing it over and over again is just crazy.

Adding new system calls because glibc is crazy is insane.

       Linus

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