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DateWed, 20 Oct 2010 04:56:52 +0200
FromIngo Molnar <>
SubjectRe: [RFC/RFT PATCH] sched: automated per tty task groups

* Mike Galbraith <efault@gmx.de> wrote:

> > On Tue, 2010-10-19 at 08:28 -0700, Linus Torvalds wrote:
> > >
> > > If people compare with a non-CGROUP_SCHED
> > > kernel, will a desktop-optimized kernel suddenly have horrible pipe
> > > latency due to much higher scheduling cost? Right now that whole
> > > feature is hidden by EXPERIMENTAL, I don't know how much it hurts, and
> > > I never timed it when I tried it out long ago..
>
> Q/D test of kernels w/wo, with same .config using pipe-test (pure sched) gives on
> my box ~590khz with tty_sched active, 620khz without cgroups acitve in same
> kernel/config without patch. last time I measured stripped down config (not long
> ago, but not yesterday either) gave max ctx rate ~690khz on this box.
>
> (note: very Q, very D numbers, no variance testing, ballpark)

That's 5% overhead in context switches. Definitely not in the 'horrible' category.

This would be a rather tempting item for 2.6.37 ... especially as it really mainly
reuses existing group scheduling functionality, in a clever way.

Mind doing more of the tty->desktop renames/generalizations as Linus suggested, and
resend the patch?

I'd also suggest to move it out of EXPERIMENTAL - we dont really do that for core
kernel features as most distros enable CONFIG_EXPERIMENTAL so it's a rather
meaningless distinction. Since the feature is default-n, people will get the old
scheduler by default but can also choose this desktop-centric scheduling mode.

I'd even argue to make it default-y, because this patch clearly cures a form of
kbuild cancer.

Thanks,

Ingo


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