Re: Mainline kernel OLTP performance update

Matthew Wilcox
2009-01-15T01:22:06Z

On Wed, Jan 14, 2009 at 04:35:57PM -0800, Andrew Morton wrote:
> On Tue, 13 Jan 2009 15:44:17 -0700
> "Wilcox, Matthew R" <matthew.r.wilcox@intel.com> wrote:
> >
>
> (top-posting repaired. That @intel.com address is a bad influence ;))

Alas, that email address goes to an Outlook client. Not much to be done
about that.

> (cc linux-scsi)
>
> > > This is latest 2.6.29-rc1 kernel OLTP performance result. Compare to
> > > 2.6.24.2 the regression is around 3.5%.
> > >
> > > Linux OLTP Performance summary
> > > Kernel# Speedup(x) Intr/s CtxSw/s us% sys% idle% iowait%
> > > 2.6.24.2 1.000 21969 43425 76 24 0 0
> > > 2.6.27.2 0.973 30402 43523 74 25 0 1
> > > 2.6.29-rc1 0.965 30331 41970 74 26 0 0

> But the interrupt rate went through the roof.

Yes. I forget why that was; I'll have to dig through my archives for
that.

> A 3.5% slowdown in this workload is considered pretty serious, isn't it?

Yes. Anything above 0.3% is statistically significant. 1% is a big
deal. The fact that we've lost 3.5% in the last year doesn't make
people happy. There's a few things we've identified that have a big
effect:

- Per-partition statistics. Putting in a sysctl to stop doing them gets
some of that back, but not as much as taking them out (even when
the sysctl'd variable is in a __read_mostly section). We tried a
patch from Jens to speed up the search for a new partition, but it
had no effect.

- The RT scheduler changes. They're better for some RT tasks, but not
the database benchmark workload. Chinang has posted about
this before, but the thread didn't really go anywhere.
http://marc.info/?t=122903815000001&r=1&w=2

SLUB would have had a huge negative effect if we were using it -- on the
order of 7% iirc. SLQB is at least performance-neutral with SLAB.

--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."