Messages in this thread | | | Date | Tue, 29 Jul 2014 11:39:11 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/2 v4] sched: Rewrite per entity runnable load average tracking |
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On Tue, Jul 29, 2014 at 11:12:37AM +0200, Vincent Guittot wrote: > On 27 July 2014 19:36, Yuyang Du <yuyang.du@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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