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+55aFz6SxLEr0MNubz7rcwcqki7EM33Vp-q3KFEvuLG6a61ZQ@mail.gmail.com>
Date:	Fri, 14 Sep 2012 14:44:48 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Borislav Petkov <bp@...en8.de>,
	Nikolay Ulyanitsky <lystor@...il.com>,
	Mike Galbraith <efault@....de>, 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>
Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to
 3.6-rc5 on AMD chipsets - bisected

On Fri, Sep 14, 2012 at 2:40 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>
> The problem the patch is trying to address is not having to scan an
> entire package for idle cores on every wakeup now that packages are
> getting stupid big.

No, it does something *else* too. That whole "left-right" logic to
(according to the commit message) "prevent bouncing" is entirely new,
afaik.

So it is *not* just about avoiding to have to scan the whole package.
It changes actual semantics too. No?

            Linus
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