linux-kernel - Re: [PATCH] sched/fair: fix runnable

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Message-ID: <xm26r1yhtbjr.fsf@bsegall-linux.svl.corp.google.com>
Date:   Wed, 26 Feb 2020 11:04:40 -0800
From:   bsegall@...gle.com
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, linux-kernel@...r.kernel.org, pauld@...hat.com,
        parth@...ux.ibm.com, valentin.schneider@....com, hdanton@...a.com,
        zhout@...aldi.net
Subject: Re: [PATCH] sched/fair: fix runnable_avg for throttled cfs

Vincent Guittot <vincent.guittot@...aro.org> writes:

> When a cfs_rq is throttled, its group entity is dequeued and its running
> tasks are removed. We must update runnable_avg with current h_nr_running
> and update group_se->runnable_weight with new h_nr_running at each level
> of the hierarchy.

You'll also need to do this for task enqueue/dequeue inside of a
throttled hierarchy, I'm pretty sure.

>
> Fixes: 9f68395333ad ("sched/pelt: Add a new runnable average signal")
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
> This patch applies on top of tip/sched/core
>
>  kernel/sched/fair.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index fcc968669aea..6d46974e9be7 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4703,6 +4703,11 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
>  
>  		if (dequeue)
>  			dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP);
> +		else {
> +			update_load_avg(qcfs_rq, se, 0);
> +			se_update_runnable(se);
> +		}
> +
>  		qcfs_rq->h_nr_running -= task_delta;
>  		qcfs_rq->idle_h_nr_running -= idle_task_delta;
>  
> @@ -4772,6 +4777,11 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
>  		cfs_rq = cfs_rq_of(se);
>  		if (enqueue)
>  			enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
> +		else {
> +			update_load_avg(cfs_rq, se, 0);


> +			se_update_runnable(se);
> +		}
> +
>  		cfs_rq->h_nr_running += task_delta;
>  		cfs_rq->idle_h_nr_running += idle_task_delta;