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Message-ID: <Yv4W5u4+CXir3bjZ@worktop.programming.kicks-ass.net>
Date: Thu, 18 Aug 2022 12:39:34 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Chengming Zhou <zhouchengming@...edance.com>
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 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.
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