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

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Date:	Thu, 16 Jun 2011 17:24:04 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Andrew Morton <akpm@...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


> The fact is, glibc is just total crap.
>
> I tried to send uli a patch to just add caching. No go. I sent
> *another* patch to at least make glibc use a sane interface (and the
> cache if it needs to fall back on /proc/stat for some legacy reason).
> We'll see what happens.

FWIW a rerun with this modified LD_PRELOAD that does caching seems
to have the same performance as the version that does sched_getaffinity.

So you're right. Caching indeed helps and my assumption that the child
would only do it once was incorrect.

The only problem I see with it is that it doesn't handle CPU hotplug,
but Paul's suggestion would fix that too.

> Paul Eggbert suggested "caching for one second" - by just calling
> "gettimtofday()" to see how old the cache is. That would work too.
>

Maybe we need a "standard LD_PRELOAD library to improve glibc" @)

-Andi


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