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Date: Thu, 18 Aug 2022 19:03:11 +0800 From: Chengming Zhou <zhouchengming@...edance.com> To: Peter Zijlstra <peterz@...radead.org> Cc: vincent.guittot@...aro.org, dietmar.eggemann@....com, mingo@...hat.com, rostedt@...dmis.org, bsegall@...gle.com, vschneid@...hat.com, linux-kernel@...r.kernel.org, tj@...nel.org Subject: Re: [PATCH v5 8/9] sched/fair: defer task sched_avg attach to enqueue_entity() On 2022/8/18 18:39, Peter Zijlstra wrote: > On Thu, Aug 18, 2022 at 11:43:42AM +0800, Chengming Zhou wrote: >> When wake_up_new_task(), we would use post_init_entity_util_avg() >> to init util_avg/runnable_avg based on cpu's util_avg at that time, >> then attach task sched_avg to cfs_rq. >> >> Since enqueue_entity() would always attach any unattached task entity, >> so we can defer this work to enqueue_entity(). >> >> post_init_entity_util_avg(p) >> attach_entity_cfs_rq() --> (1) >> activate_task(rq, p) >> enqueue_task() := enqueue_task_fair() >> enqueue_entity() >> update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH) >> if (!se->avg.last_update_time && (flags & DO_ATTACH)) >> attach_entity_load_avg() --> (2) >> >> This patch defer attach from (1) to (2) >> >> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com> >> --- >> kernel/sched/fair.c | 4 ---- >> 1 file changed, 4 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index e0d34ecdabae..aacf38a72714 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -799,8 +799,6 @@ void init_entity_runnable_average(struct sched_entity *se) >> /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */ >> } >> >> -static void attach_entity_cfs_rq(struct sched_entity *se); >> - >> /* >> * With new tasks being created, their initial util_avgs are extrapolated >> * based on the cfs_rq's current util_avg: >> @@ -863,8 +861,6 @@ void post_init_entity_util_avg(struct task_struct *p) >> se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq); >> return; >> } >> - >> - attach_entity_cfs_rq(se); >> } > > There are comments with update_cfs_rq_load_avg() and > remove_entity_load_avg() that seem to rely on post_init_entity_util() > doing this attach. > > If that is no longer true; at the very least those comments need to be > updated, but also, I don't immediately see why that's no longer the > case, so please explain. This attach in post_init_entity_util() will be done in enqueue_entity() -> update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH) loop. So these comments should be updated in the next version. Thanks!
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