Messages in this thread | | | Date | Thu, 31 Mar 2022 13:47:09 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/2] sched/fair: Simple runqueue order on migrate |
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It's been 3 months since I wrote these patches, so memory is vague at best :/
On Tue, Mar 29, 2022 at 11:03:44AM +0200, Vincent Guittot wrote:
> > +static void place_entity_migrate(struct cfs_rq *cfs_rq, struct sched_entity *se) > > +{ > > + if (!sched_feat(PLACE_MIGRATE)) > > + return; > > + > > + if (cfs_rq->nr_running < se->migrated) { > > + /* > > + * Migrated to a shorter runqueue, go first because > > + * we were under-served on the old runqueue. > > + */ > > + se->vruntime = cfs_rq->min_vruntime; > > + return; > > + } > > + > > + /* > > + * Migrated to a longer runqueue, go last because > > + * we got over-served on the old runqueue. > > + */ > > + se->vruntime = cfs_rq->min_vruntime + sched_vslice(cfs_rq, se); > > +} > > + > > static void check_enqueue_throttle(struct cfs_rq *cfs_rq); > > > > static inline bool cfs_bandwidth_used(void); > > @@ -4296,6 +4317,8 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > > > > if (flags & ENQUEUE_WAKEUP) > > place_entity(cfs_rq, se, 0); > > + else if (se->migrated) > > + place_entity_migrate(cfs_rq, se); > > > > check_schedstat_required(); > > update_stats_enqueue_fair(cfs_rq, se, flags);
> > @@ -6973,14 +6997,15 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) > > * wakee task is less decayed, but giving the wakee more load > > * sounds not bad. > > */ > > - remove_entity_load_avg(&p->se); > > + remove_entity_load_avg(se); > > } > > > > /* Tell new CPU we are migrated */ > > - p->se.avg.last_update_time = 0; > > + se->avg.last_update_time = 0; > > > > /* We have migrated, no longer consider this task hot */ > > - p->se.migrated = 1; > > + for_each_sched_entity(se) > > + se->migrated = READ_ONCE(cfs_rq_of(se)->nr_running) + !se->on_rq; > > Why do we need to loop on se ? Isn't p->se enough ?
Yeah; I really don't recall why I did that. And looking at it now, it doesn't really make much sense. I suppose it will trigger place_entity_migrate() for the group entries, but on the old CPU.
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