Re: [RFC patch 1/2] sched: dynamically adapt granularity with nr_running

Mathieu Desnoyers
2010-09-12T18:16:28Z

* Mike Galbraith (efault@gmx.de) wrote:
> On Sun, 2010-09-12 at 08:14 +0200, Ingo Molnar wrote:
> > * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> >
> > > (on a uniprocessor 2.0 GHz Pentium M)
> > >
> > > * Without the patch:
> > >
> > > - wakeup-latency with SIGEV_THREAD in parallel with youtube video and
> > > make -j10
> > >
> > > maximum latency: 50107.8 µs
> > > average latency: 6609.2 µs
> > > missed timer events: 0
> >
> > I tried your patches on a similar UP system, using wakeup-latency.c. I
> > also measured the vanilla upstream kernel (cced86a) with the default
> > granularity settings, and also vanilla with a sched_min_granularity/3
> > tune (patch attached below for that).
> >
> > I got the following results (make -j10 kbuild load, average of 3 runs):
> >
> > vanilla:
> >
> > maximum latency: 38278.9 µs
> > average latency: 7730.1 µs
> >
> > mathieu-dyn:
> >
> > maximum latency: 28698.8 µs
> > average latency: 7757.1 µs
> >
> > peterz-min_gran/3:
> >
> > maximum latency: 22702.1 µs
> > average latency: 6684.8 µs
>
> One thing that springs to mind with make is that it does vfork, so kinda
> sorta continues running in drag, so shouldn't get credit for sleeping,
> as that introduces bogus spread. Post vfork parent notification time
> adjustment may suffice, think I'll try that.

Hrm, I might be misunderstanding what you are saying here, but when a new
process/thread is forked and woken up, we fall in the "initial" case of
place_entity, so we increase the vruntime of a whole slice rather than getting
credit for sleeping.

Or am I missing your point ?

Thanks,

Mathieu

--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.