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SubjectRe: scheduler oddity [bug?]
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On Sun, 2009-03-08 at 18:52 +0100, Ingo Molnar wrote:
> * Mike Galbraith <efault@gmx.de> wrote:
>
> > On Sun, 2009-03-08 at 16:39 +0100, Ingo Molnar wrote:
> > > * Mike Galbraith <efault@gmx.de> wrote:
> > >
> > > > The problem with your particular testcase is that while one
> > > > half has an avg_overlap (what we use as affinity hint for
> > > > synchronous wakeups) which triggers the affinity hint, the
> > > > other half has avg_overlap of zero, what it was born with, so
> > > > despite significant execution overlap, the scheduler treats
> > > > them as if they were truly synchronous tasks.
> > >
> > > hm, why does it stay on zero?
> >
> > Wakeup preemption. Presuming here: heavy task wakes light
> > task, is preempted, light task stuffs data into pipe, heavy
> > task doesn't block, so no avg_overlap is ever computed. The
> > heavy task uses 100% CPU.
> >
> > Running as SCHED_BATCH (virgin source), it becomes sane.
>
> ah.
>
> I'd argue then that time spent on the rq preempted _should_
> count in avg_overlap statistics. I.e. couldnt we do something
> like ... your patch? :)
>
> > > if (sleep && p->se.last_wakeup) {
> > > update_avg(&p->se.avg_overlap,
> > > p->se.sum_exec_runtime - p->se.last_wakeup);
> > > p->se.last_wakeup = 0;
> > > - }
> > > + } else if (p->se.avg_overlap < limit && runtime >= limit)
> > > + update_avg(&p->se.avg_overlap, runtime);
>
> Just done unconditionally, i.e. something like:
>
> if (sleep) {
> runtime = p->se.sum_exec_runtime - p->se.last_wakeup;
> p->se.last_wakeup = 0;
> } else {
> runtime = p->se.sum_exec_runtime - p->se.prev_sum_exec_runtime;
> }
>
> update_avg(&p->se.avg_overlap, runtime);
>
> ?

That'll do it for this load. I'll resume in the a.m., give that some
testing, and try to remember all the things I was paranoid about.
(getting interrupted a _lot_.. i give up on today;)

-Mike



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