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

Mike Galbraith
2012-09-25T01:57:45Z

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