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SubjectRe: scheduler oddity [bug?]

* 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);

?

Ingo


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