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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: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andreas Herrmann <andreas.herrmann3@amd.com>,
        Nikolay Ulyanitsky <lystor@gmail.com>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Date: Sat, 15 Sep 2012 06:42:17 +0200
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On Fri, 2012-09-14 at 21:15 -0700, Linus Torvalds wrote:
> We don't do random crazy "use another scheduler" to hide problems with
> the default one.

I was proposing a diagnostic.
> 
> And since you are the author of the regressing patch, and don't seem
> to treat the regression as something serious, I really see no
> alternative to just reverting it.

Wow, I don't know how you obtained that impression, but fine, nuke it.

>       Linus
> 
> On Sep 14, 2012 9:11 PM, "Mike Galbraith" <efault@gmx.de> wrote:
>         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
>