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: <1348544636.7100.53.camel@marge.simpson.net>
Date:	Tue, 25 Sep 2012 05:43:56 +0200
From:	Mike Galbraith <efault@....de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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, 2012-09-24 at 20:32 -0700, Linus Torvalds wrote: 
> 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.

prev_cpu can be anywhere, so buddies sometimes need help getting back
together when they've been disrupted, but yeah, in the general case it's
local, so you want prev_cpu if it can be had.

-Mike

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