Messages in this thread | | | Date | Fri, 10 Jun 2022 18:55:29 +0800 | Subject | Re: [External] Re: [PATCH v2] sched/fair: combine detach into dequeue when migrating task | From | Chengming Zhou <> |
| |
Hi,
On 2022/6/10 18:49, Dietmar Eggemann wrote: > 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.
Yes.
> > [...] > >> @@ -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)))
Better, will do.
> >> + 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) */
Thanks for the description, it's clearer, I should put it in the commit message.
> > [...] > >> @@ -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)) {
Will do. Thanks!
> > [...]
| |