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: <1348724661.7059.124.camel@marge.simpson.net>
Date:	Thu, 27 Sep 2012 07:44:21 +0200
From:	Mike Galbraith <efault@....de>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Thu, 2012-09-27 at 07:18 +0200, Borislav Petkov wrote: 
> On Thu, Sep 27, 2012 at 07:09:28AM +0200, Mike Galbraith wrote:
>  but how does that affect pgbench and ilk that must spread regardless
> > of footprints.
> 
> Well, how do you measure latency of the 1 process in the 1:N case? Maybe
> pipeline stalls of the 1 along with some way to recognize it is the 1 in
> the 1:N case.

Best is to let userland tell us it's critical.  Smarts are expensive.  A
class of it's own (my wakees do _not_ preempt me, and I don't care that
you think this is unfair to the unwashed masses who will otherwise
_starve_ without me feeding them) makes sense for these guys.

-Mike

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