Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to3.6-rc5 on AMD chipsets - bisected

From: Peter Zijlstra
Date: Fri Sep 14 2012 - 17:56:23 EST

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@xxxxxxxxx> 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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