linux-kernel - Re: [PATCH] sched/rt: Don't active rt throtting when no running cfs task

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Date:   Tue, 16 Jun 2020 09:50:27 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Lichao Liu <liulichao@...ngson.cn>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/rt: Don't active rt throtting when no running cfs
 task

On Tue, 16 Jun 2020 20:37:29 +0800
Lichao Liu <liulichao@...ngson.cn> wrote:

> Active rt throtting will dequeue rt_rq from rq at least 50ms,
> When there is no running cfs task, do we still active it?
> 

This is something I would like to have.

Peter, what's your thought on this?

-- Steve

> Signed-off-by: Lichao Liu <liulichao@...ngson.cn>
> ---
>  kernel/sched/rt.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index df11d88c9895..d6524347cea0 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -961,12 +961,13 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
>  
>  	if (rt_rq->rt_time > runtime) {
>  		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
> +		struct rq *rq = rq_of_rt_rq(rt_rq);
>  
>  		/*
>  		 * Don't actually throttle groups that have no runtime assigned
>  		 * but accrue some time due to boosting.
>  		 */
> -		if (likely(rt_b->rt_runtime)) {
> +		if (likely(rt_b->rt_runtime) && rq->cfs.nr_running > 0) {
>  			rt_rq->rt_throttled = 1;
>  			printk_deferred_once("sched: RT throttling activated\n");
>  		} else {