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Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to
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From: Mike Galbraith <efault@gmx.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Mel Gorman <mgorman@suse.de>,
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        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
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Date: Tue, 25 Sep 2012 03:39:46 +0200
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On Mon, 2012-09-24 at 12:12 -0700, Linus Torvalds wrote: 
> On Mon, Sep 24, 2012 at 11:26 AM, Mike Galbraith <efault@gmx.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