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: <1347659777.7172.97.camel@twins>
Date:	Fri, 14 Sep 2012 23:56:17 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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, 2012-09-14 at 14:44 -0700, Linus Torvalds wrote:
> 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?

Both things change semantics, not looking at the entire package is new
too. But yeah I guess you could look at the exact cross-stitching as an
enhancement to the 'idle_buggy' thing.


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