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+55aFwb1ddBr6gEsJ7jBjGeBC5Son5p3s9nsx_Hyst9E-Hhpg@mail.gmail.com>
Date:	Mon, 24 Sep 2012 20:32:43 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mike Galbraith <efault@....de>
Cc:	Borislav Petkov <bp@...en8.de>,
	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 Mon, Sep 24, 2012 at 8:20 PM, Mike Galbraith <efault@....de> wrote:
>
> Yes.  Cross wiring traverse _start_ points should eliminate (well, damp)
> bounce as well without killing the 1:N latency/preempt benefits of large
> L3 packages.

Yes, a "test buddy first, then check the other cores in the package"
hybrid approach might be reasonable.

Of course, that's effectively what the whole "prev_cpu" thing is kind
of supposed to also do, isn't it? Because it's even lovelier if you
can avoid bouncing around by trying to hit a previous CPU that might
just have some of the old data in the caches still.

      Linus
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