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Date:	Thu, 16 Jun 2011 17:24:04 -0700
From:	Andi Kleen <>
To:	Linus Torvalds <>
CC:	Peter Zijlstra <>,
	Tim Chen <>,
	Shaohua Li <>,
	Andrew Morton <>,
	Hugh Dickins <>,
	KOSAKI Motohiro <>,
	Benjamin Herrenschmidt <>,
	David Miller <>,
	Martin Schwidefsky <>,
	Russell King <>,
	Paul Mundt <>,
	Jeff Dike <>,
	Richard Weinberger <>,
	"Luck, Tony" <>,
	KAMEZAWA Hiroyuki <>,
	Mel Gorman <>, Nick Piggin <>,
	Namhyung Kim <>,
	"Shi, Alex" <>,
	"" <>,
	"" <>,
	"Rafael J. Wysocki" <>
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" @)


View attachment "sysconf-caching.c" of type "text/plain" (472 bytes)

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