Re: [PATCH] sched/fair: Fix non-empty throttled_limbo_list warning in tg_throttle_down()

[Hao Jia <jiahao.kernel@gmail.com>]

Hi Prateek,

On 2025/10/24 12:36, K Prateek Nayak wrote:
> 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 for your suggestion. This is indeed a potential risk, and it will 
do it in the next version.

Thanks,
Hao