linux-kernel - Re: [Bugme-new] [Bug 15618] New: 2.6.18->2.6.32->2.6.33 huge regression in performance

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Message-Id: <20100323111351.756c8752.akpm@linux-foundation.org>
Date:	Tue, 23 Mar 2010 11:13:51 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org, ant.starikov@...il.com,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [Bugme-new] [Bug 15618] New: 2.6.18->2.6.32->2.6.33 huge
 regression in performance

On Tue, 23 Mar 2010 18:34:09 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> It shows a very brutal amount of page fault invoked mmap_sem spinning 
> overhead.
> 

Yes.  Note that we fall off a cliff at nine threads on a 16-way.  As
soon as a core gets two threads scheduled onto it?  Probably triggered
by an MM change, possibly triggered by a sched change which tickled a
preexisting MM shortcoming.  Who knows.

Anton, we have an executable binary in the bugzilla report but it would
be nice to also have at least a description of what that code is
actually doing.  A quick strace shows quite a lot of mprotect activity.
A pseudo-code walkthrough, perhaps?

Thanks.
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