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

Mike Galbraith
2012-09-15T04:42:23Z

On Fri, 2012-09-14 at 21:15 -0700, Linus Torvalds wrote:
> We don't do random crazy "use another scheduler" to hide problems with
> the default one.

I was proposing a diagnostic.
>
> And since you are the author of the regressing patch, and don't seem
> to treat the regression as something serious, I really see no
> alternative to just reverting it.

Wow, I don't know how you obtained that impression, but fine, nuke it.

> Linus
>
> On Sep 14, 2012 9:11 PM, "Mike Galbraith" <efault@gmx.de> wrote:
> On Fri, 2012-09-14 at 23:27 +0200, Borislav Petkov wrote:
> > (Adding everybody to CC and leaving the below for
> reference.)
> >
> > Guys,
> >
> > as Nikolay says below, we have a regression in 3.6 with
> pgbench's
> > benchmark in postgresql.
> >
> > I was able to reproduce it on another box here and did a
> bisection run.
> > It pointed to the commit below.
> >
> > And yes, reverting that commit fixes the issue here.
>
> My wild (and only) theory is that this is userspace spinlock
> related.
> If so, starting the server and benchmark SCHED_BATCH should
> not only
> kill the regression, but likely improve throughput as well.
>
> -Mike
>