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Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to
 3.6-rc5 on AMD chipsets - bisected
From: Mike Galbraith <efault@gmx.de>
To: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, Mel Gorman <mgorman@suse.de>,
        Nikolay Ulyanitsky <lystor@gmail.com>, linux-kernel@vger.kernel.org,
        Andreas Herrmann <andreas.herrmann3@amd.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Suresh Siddha <suresh.b.siddha@intel.com>
Date: Tue, 25 Sep 2012 03:57:38 +0200
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On Mon, 2012-09-24 at 21:20 +0200, Borislav Petkov wrote: 
> On Mon, Sep 24, 2012 at 12:12:18PM -0700, Linus Torvalds wrote:
> > On Mon, Sep 24, 2012 at 11:26 AM, Mike Galbraith <efault@gmx.de> wrote:
> > >
> > > Aside from the cache pollution I recall having been mentioned, on my
> > > E5620, cross core is a tbench win over affine, cross thread is not.
> > 
> > Oh, I agree with trying to avoid HT threads, the resource contention
> > easily gets too bad.
> > 
> > It's more a question of "if we have real cores with separate L1's but
> > shared L2's, go with those first, before we start distributing it out
> > to separate L2's".
> 
> Yes, this is exactly what I meant before. We basically want to avoid
> unnecessary, high-volume probe traffic over the L3 or memory controller,
> if possible.
> 
> So, trying harder to select an L2 sibling would be more beneficial,
> IMHO, instead of scanning the whole node.

If those L2 siblings are cores, oh yeah.  Do any modern packages have
multi-core shared L2?

-Mike