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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: Borislav Petkov <bp@alien8.de>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
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        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Suresh Siddha <suresh.b.siddha@intel.com>
Date: Tue, 25 Sep 2012 04:49:26 +0200
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On Mon, 2012-09-24 at 19:11 -0700, Linus Torvalds wrote:

> In the not-so-distant past, we had the intel "Dunnington" Xeon, which
> was iirc basically three Core 2 duo's bolted together (ie three
> clusters of two cores sharing L2, and a fully shared L3). So that was
> a true multi-core with fairly big shared L2, and it really would be
> sad to not use the second core aggressively.

Ah.  That's what I did to select_idle_sibling() in a nutshell, converted
the problematic large L3 packages into multiple ~core2duo pairs, modulo
shared L2 'course.  Bounce proof, and on Westmere, the jabbering back
and forth in L3 somehow doesn't hurt as much as expected, so the things
act (more or less, L2 traffic _does_ matter;) like the real deal.

-Mike