linux-kernel - Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets

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Date:	Tue, 25 Sep 2012 03:39:46 +0200
From:	Mike Galbraith <efault@....de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>, Borislav Petkov <bp@...en8.de>,
	Nikolay Ulyanitsky <lystor@...il.com>,
	linux-kernel@...r.kernel.org,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to
 3.6-rc5 on AMD chipsets - bisected

On Mon, 2012-09-24 at 12:12 -0700, Linus Torvalds wrote: 
> On Mon, Sep 24, 2012 at 11:26 AM, Mike Galbraith <efault@....de> wrote:
> >
> > Aside from the cache pollution I recall having been mentioned, on my
> > E5620, cross core is a tbench win over affine, cross thread is not.
> 
> Oh, I agree with trying to avoid HT threads, the resource contention
> easily gets too bad.
> 
> It's more a question of "if we have real cores with separate L1's but
> shared L2's, go with those first, before we start distributing it out
> to separate L2's".

Oh absolutely, if you have cores with shared L2, that's _the_ way to go,
shared L2 is lovely, and what select_idle_sibling() was originally all
about.  Westmere manages to cough up a tbench win without that.  Heck, I
generated some numbers for Borislav yesterday showing the thing winning
at _netperf TCP_RR_, one byte synchronous ping pong.

-Mike

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