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: <1347682262.4340.160.camel@marge.simpson.net>
Date:	Sat, 15 Sep 2012 06:11:02 +0200
From:	Mike Galbraith <efault@....de>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Nikolay Ulyanitsky <lystor@...il.com>,
	linux-kernel@...r.kernel.org,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to
 3.6-rc5 on AMD chipsets - bisected

On Fri, 2012-09-14 at 23:27 +0200, Borislav Petkov wrote: 
> (Adding everybody to CC and leaving the below for reference.)
> 
> Guys,
> 
> as Nikolay says below, we have a regression in 3.6 with pgbench's
> benchmark in postgresql.
> 
> I was able to reproduce it on another box here and did a bisection run.
> It pointed to the commit below.
> 
> And yes, reverting that commit fixes the issue here.

My wild (and only) theory is that this is userspace spinlock related.
If so, starting the server and benchmark SCHED_BATCH should not only
kill the regression, but likely improve throughput as well.

-Mike

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