Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets - bisected

Peter Zijlstra
2012-09-14T21:59:48Z

On Fri, 2012-09-14 at 23:56 +0200, Peter Zijlstra wrote:
> 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@chello.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.

What I'm saying is that having an idle_buggy means you have to assign
one in the first place, his left-right stuff might not be the simplest
means to do that -- in fact I suggested he do a simple shift first time
I saw that patch.

So if not the left-right thing, you still need to do _something_ to make
the idle_buggy work at all. So its not entirely separate.