Re: [RFC/RFT PATCH] sched: automated per tty task groups

[Ingo Molnar]

* Mike Galbraith <efault@xxxxxx> 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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