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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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