Re: [PATCH v2] sched/freq: move call to cpufreq_update_util

[Vincent Guittot]

Le Wednesday 13 Nov 2019 à 15:09:47 (+0100), Dietmar Eggemann a écrit :
> On 13.11.19 14:30, Vincent Guittot wrote:
> > On Wed, 13 Nov 2019 at 11:50, Dietmar Eggemann <dietmar.eggemann@xxxxxxx> wrote:
> >>
> >> On 12.11.19 16:05, Vincent Guittot wrote:
> >>> Le Tuesday 12 Nov 2019 à 15:48:13 (+0100), Vincent Guittot a écrit :
> 
> [...]
> 
> >>>> @@ -7493,9 +7495,9 @@ static void update_blocked_averages(int cpu)
> >>>>       * that RT, DL and IRQ signals have been updated before updating CFS.
> >>>>       */
> >>>>      curr_class = rq->curr->sched_class;
> >>>> -    update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
> >>>> -    update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
> >>>> -    update_irq_load_avg(rq, 0);
> >>>> +    decayed |= update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
> >>>> +    decayed |= update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
> >>>> +    decayed |= update_irq_load_avg(rq, 0);
> >>
> >> Why not 'decayed  = update_cfs_rq_load_avg()' like in the
> >> !CONFIG_FAIR_GROUP_SCHED case?
> > 
> > Because it is handled by the update_load_avg() in
> > for_each_leaf_cfs_rq_safe() loop
> > 
> > This means that we can have 2 calls to cpufreq_update_util in
> > update_blocked_average() but at least the values will be up to date in
> > both calls unlike previously.
> > 
> > I'm going to prepare an additional patch to remove this useless call.
> > I have also seen some possible further optimization that i need to
> > study a bit more before preparing a patch
> 
> I see. The update_load_avg() call for the taskgroup skeleton se
> (cfs_rq->tg->se[cpu]). But what happens to the cpu which only has the
> root cfs_rq i the list? It doesn't have a skeleton se.

you're right. I have to add the following to make sure it will be called

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2eb1aa8..9fc077c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7604,9 +7604,13 @@ static void update_blocked_averages(int cpu)
                        cpu,
                        cfs_rq == &rq->cfs ? 0 : (long)cfs_rq->tg );
 
-               if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq))
+               if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq)) {
                        update_tg_load_avg(cfs_rq, 0);
 
+                       if (cfs_rq == &rq->cfs)
+                               decayed = 1;
+               }
+
                trace_sched_load_contrib_blocked(cpu,
                        &cfs_rq->avg,
                        cfs_rq == &rq->cfs ? 0 : (long)cfs_rq->tg );