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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Message-ID: <20120924192056.GB4082@liondog.tnic>
Date:	Mon, 24 Sep 2012 21:20:56 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.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, Sep 24, 2012 at 12:12:18PM -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".

Yes, this is exactly what I meant before. We basically want to avoid
unnecessary, high-volume probe traffic over the L3 or memory controller,
if possible.

So, trying harder to select an L2 sibling would be more beneficial,
IMHO, instead of scanning the whole node.

-- 
Regards/Gruss,
    Boris.
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