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Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to
 3.6-rc5 on AMD chipsets - bisected
From: Mike Galbraith <efault@gmx.de>
To: Borislav Petkov <bp@alien8.de>
Cc: Nikolay Ulyanitsky <lystor@gmail.com>, linux-kernel@vger.kernel.org,
        Andreas Herrmann <andreas.herrmann3@amd.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>
Date: Sat, 15 Sep 2012 06:11:02 +0200
In-Reply-To: <20120914212717.GA29307@liondog.tnic>
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	 <20120914212717.GA29307@liondog.tnic>
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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