Messages in this thread Patch in this message | | | Date | Fri, 10 Jun 2022 12:49:00 +0200 | Subject | Re: [PATCH v2] sched/fair: combine detach into dequeue when migrating task | From | Dietmar Eggemann <> |
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On 09/06/2022 05:53, Chengming Zhou wrote: > When we are migrating task out of the CPU, we can combine detach > into dequeue_entity() to save the independent detach_entity_cfs_rq() > in migrate_task_rq_fair(). > > This optimization is like combining DO_ATTACH in the enqueue_entity() > when migrating task to the CPU. > > So we don't have to traverse the CFS tree twice to do these load > detach and propagation.
By `propagation` you refer to the detach_entity_cfs_rq() -> propagate_entity_cfs_rq() call? This one wouldn't be called anymore with your change.
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> @@ -4426,6 +4435,14 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq); > static void > dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > { > + int action = UPDATE_TG; > + > + /* > + * If we are migrating task from the CPU, detach load_avg when dequeue. > + */ > + if (entity_is_task(se) && task_of(se)->on_rq == TASK_ON_RQ_MIGRATING)
- if (entity_is_task(se) && task_of(se)->on_rq == TASK_ON_RQ_MIGRATING) + if (entity_is_task(se) && task_on_rq_migrating(task_of(se)))
> + action |= DO_DETACH;
With the `entity_is_task(se)` you make sure we only call detach_entity_load_avg() and update_tg_load_avg() for the se representing the task itself (and not taskgroups the task might run in). So IMHO this looks good.
You save the propagate_entity_cfs_rq(&p->se) call from (2) by doing the detach_entity_load_avg(), update_tg_load_avg() for a migrating task inside (1) (the task being the first se in the loop )
detach_task() deactivate_task() dequeue_task_fair() for_each_sched_entity(se) dequeue_entity() update_load_avg() /* (1) */
set_task_cpu() migrate_task_rq_fair() /* called detach_entity_cfs_rq() before the patch (2) */
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> @@ -6940,15 +6957,10 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) > se->vruntime -= min_vruntime; > } > > - if (p->on_rq == TASK_ON_RQ_MIGRATING) { > - /* > - * In case of TASK_ON_RQ_MIGRATING we in fact hold the 'old' > - * rq->lock and can modify state directly. > - */ > - lockdep_assert_rq_held(task_rq(p)); > - detach_entity_cfs_rq(&p->se); > - > - } else { > + /* > + * In case of TASK_ON_RQ_MIGRATING we already detach in dequeue_entity. > + */ > + if (p->on_rq != TASK_ON_RQ_MIGRATING) {
- if (p->on_rq != TASK_ON_RQ_MIGRATING) { + if (!task_on_rq_migrating(p)) {
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