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: <CA+55aFwSapFvbRJ-mCL+vUTvJwDufVPQR7q92KNA=eWiSKo2sg@mail.gmail.com>
Date:	Thu, 27 Sep 2012 11:15:47 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	david@...g.hm
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <bp@...en8.de>, Mike Galbraith <efault@....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 Thu, Sep 27, 2012 at 10:45 AM,  <david@...g.hm> wrote:
>
> For the initial starup of a new process, finding as idle and remote a core
> to start on (minimum sharing with existing processes) is probably the smart
> thing to do.

Actually, no.

It's *exec* that should go remote. New processes (fork, vfork or
clone) absolutely should *not* go remote at all.

vfork() should stay on the same CPU (synchronous wakeup), fork()
should possibly go SMT (likely exec in the near future will spread it
out), and clone should likely just stay close too.

           Linus
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