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 13:58:06 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mike Galbraith <efault@....de>, Borislav Petkov <bp@...en8.de>,
	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, 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 indeed. My Core2Quad didn't have an L3 afaik (its sitting around
without a PSU atm so checking gets a little hard) so the LLC level was
the L2 and all worked out right (it also not having SMT helped of
course).

But if there was a Xeon chip that did add a package L3 then yes, all
this would become more interesting still. We'd need to extend the
scheduler topology a bit as well, I don't think it can currently handle
this well.

So I guess we get to do some work for steamroller.
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