linux-kernel - Re: [PATCH] sched/fair: update tg->load_avg and se->load in throttle_cfs

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Date:   Wed, 13 Apr 2022 10:30:10 -0700
From:   Benjamin Segall <bsegall@...gle.com>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, mgorman@...e.de, bristot@...hat.com,
        linux-kernel@...r.kernel.org, duanxiongchun@...edance.com,
        songmuchun@...edance.com, zhengqi.arch@...edance.com
Subject: Re: [PATCH] sched/fair: update tg->load_avg and se->load in
 throttle_cfs_rq()

Chengming Zhou <zhouchengming@...edance.com> writes:

> We use update_load_avg(cfs_rq, se, 0) in throttle_cfs_rq(), so the
> cfs_rq->tg_load_avg_contrib and task_group->load_avg won't be updated
> even when the cfs_rq's load_avg has changed.
>
> And we also don't call update_cfs_group(se), so the se->load won't
> be updated too.
>
> Change to use update_load_avg(cfs_rq, se, UPDATE_TG) and add
> update_cfs_group(se) in throttle_cfs_rq(), like we do in
> dequeue_task_fair().

Hmm, this does look more correct; Vincent, was having this not do
UPDATE_TG deliberate, or an accident that we all missed when checking?

It looks like the unthrottle_cfs_rq side got UPDATE_TG added later in
the two-loops pass, but not the throttle_cfs_rq side.

Also unthrottle_cfs_rq I'm guessing could still use update_cfs_group(se)


>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
>  kernel/sched/fair.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d4bd299d67ab..b37dc1db7be7 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4936,8 +4936,9 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
>  		if (!se->on_rq)
>  			goto done;
>  
> -		update_load_avg(qcfs_rq, se, 0);
> +		update_load_avg(qcfs_rq, se, UPDATE_TG);
>  		se_update_runnable(se);
> +		update_cfs_group(se);
>  
>  		if (cfs_rq_is_idle(group_cfs_rq(se)))
>  			idle_task_delta = cfs_rq->h_nr_running;