linux-kernel - Re: [PATCH] sched/fair: Fix non-empty throttled_limbo_list warning in tg_throttle

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Message-ID: <98c1968e-8629-43d1-a4b8-600d263bd5a1@amd.com>
Date: Fri, 24 Oct 2025 10:06:43 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Hao Jia <jiahao.kernel@...il.com>, <mingo@...hat.com>,
	<peterz@...radead.org>, <mingo@...nel.org>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
	<vschneid@...hat.com>
CC: <linux-kernel@...r.kernel.org>, Hao Jia <jiahao1@...iang.com>, Aaron Lu
	<ziqianlu@...edance.com>
Subject: Re: [PATCH] sched/fair: Fix non-empty throttled_limbo_list warning in
 tg_throttle_down()

Hello Hao,

On 10/23/2025 5:42 PM, Hao Jia wrote:
> @@ -5287,7 +5287,9 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  	se->on_rq = 1;
>  
>  	if (cfs_rq->nr_queued == 1) {
> -		check_enqueue_throttle(cfs_rq);
> +		if (!(flags & ENQUEUE_THROTTLE))
> +			check_enqueue_throttle(cfs_rq);
> +

So my only concern here is:

check_enqueue_throttle()
  account_cfs_rq_runtime()
    __account_cfs_rq_runtime()
      assign_cfs_rq_runtime()
        __assign_cfs_rq_runtime()
          start_cfs_bandwidth() /* Starts the BW timer. */

If we skip it, we wouldn't know we've run out of bandwidth until the
hierarchy is picked which would cause additional delay until the
bandwidth is replenished.

At the very least, we should pass the enqueue flags to
check_enqueue_throttle() and only skip the throttle_cfs_rq() part if
we spot ENQUEUE_THROTTLE.

Thoughts?

-- 
Thanks and Regards,
Prateek