On Tue, Jul 29, 2014 at 11:12:37AM +0200, Vincent Guittot wrote:
> On 27 July 2014 19:36, Yuyang Du <yuyang...@intel.com> wrote:
> > Hi Vincent,
> >
> > On Fri, Jul 18, 2014 at 11:43:00AM +0200, Vincent Guittot wrote:
> >> > @@ -2291,23 +2299,24 @@ static __always_inline int
> >> > __update_entity_runnable_avg(u64 now,
> >> > delta >>= 10;
> >> > if (!delta)
> >> > return 0;
> >> > - sa->last_runnable_update = now;
> >> > + sa->last_update_time = now;
> >> >
> >> > /* delta_w is the amount already accumulated against our next
> >> > period */
> >> > - delta_w = sa->runnable_avg_period % 1024;
> >> > + delta_w = sa->period_contrib;
> >> > if (delta + delta_w >= 1024) {
> >> > - /* period roll-over */
> >> > decayed = 1;
> >> >
> >> > + /* how much left for next period will start over, we
> >> > don't know yet */
> >> > + sa->period_contrib = 0;
> >> > +
> >> > /*
> >> > * Now that we know we're crossing a period boundary,
> >> > figure
> >> > * out how much from delta we need to complete the
> >> > current
> >> > * period and accrue it.
> >> > */
> >> > delta_w = 1024 - delta_w;
> >> > - if (runnable)
> >> > - sa->runnable_avg_sum += delta_w;
> >> > - sa->runnable_avg_period += delta_w;
> >> > + if (w)
> >> > + sa->load_sum += w * delta_w;
> >>
> >> Do you really need to have *w for computing the load_sum ? can't you
> >> only use it when computing the load_avg ?
> >>
> >> sa->load_avg = div_u64(sa->load_sum * w , LOAD_AVG_MAX)
> >>
> >
> > For task, assuming its load.weight does not change much, yes, we can. But
> > in theory, task's
>
> I would even say that the load_avg of a task should not be impacted by
> an old priority value. Once, the priority of a task is changed, we
> should only take into account this new priority to weight the load_avg
> of the task
So for tasks I would immediately agree, and I think for groups too,
seeing how the group weight is based off of this avg, if you then
include the old weight we'll get a feedback loop. This might not be
desired as it would counteract the SMP movement of tasks.
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