linux-kernel - Re: [RFC PATCH] sched/util_est: Do not sub the delayed-task's util-est

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Message-ID: <7dbd7dd3-dbf7-42e0-97c4-c5eb50250947@arm.com>
Date: Fri, 14 Mar 2025 13:14:33 +0000
From: Hongyan Xia <hongyan.xia2@....com>
To: Xuewen Yan <xuewen.yan@...soc.com>, dietmar.eggemann@....com,
 vincent.guittot@...aro.org, mingo@...hat.com, peterz@...radead.org,
 juri.lelli@...hat.com
Cc: rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.co, linux-kernel@...r.kernel.org, qyousef@...alina.io,
 ke.wang@...soc.com, di.shen@...soc.com, xuewen.yan94@...il.com
Subject: Re: [RFC PATCH] sched/util_est: Do not sub the delayed-task's
 util-est

On 14/03/2025 09:09, Xuewen Yan wrote:
> In cpu_util_without, When the task is in rq, we should
> sub the task's util_est, however, the delayed_task->on_rq
> is true, however, the delayed_task's util had been sub
> when sleep, so there is no need to sub the delayed task's
> util-est. So add the checking of delayed-task.
> 
> On the other hand, as said in [1], the logic of util_est's
> enqueue/dequeue could be simplified.
> So simplify it by aligning with the conditions of uclamp.
> 
> [1]https://lore.kernel.org/all/CAB8ipk8pEvOtCm-d0o1rsekwxPWUHk9iBGtt9TLTWW-iWTQKiA@mail.gmail.com/
> 
> Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
> ---
>   kernel/sched/fair.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c798d2795243..bebf40a0fa4e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6930,7 +6930,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>   	 * Let's add the task's estimated utilization to the cfs_rq's
>   	 * estimated utilization, before we update schedutil.
>   	 */
> -	if (!(p->se.sched_delayed && (task_on_rq_migrating(p) || (flags & ENQUEUE_RESTORE))))
> +	if (!p->se.sched_delayed || (flags & ENQUEUE_DELAYED))
>   		util_est_enqueue(&rq->cfs, p);
>   
>   	if (flags & ENQUEUE_DELAYED) {
> @@ -7168,7 +7168,7 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
>    */
>   static bool dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>   {
> -	if (!(p->se.sched_delayed && (task_on_rq_migrating(p) || (flags & DEQUEUE_SAVE))))
> +	if (!p->se.sched_delayed)
>   		util_est_dequeue(&rq->cfs, p);
>   
>   	util_est_update(&rq->cfs, p, flags & DEQUEUE_SLEEP);
> @@ -8037,7 +8037,8 @@ cpu_util(int cpu, struct task_struct *p, int dst_cpu, int boost)
>   		 */
>   		if (dst_cpu == cpu)
>   			util_est += _task_util_est(p);
> -		else if (p && unlikely(task_on_rq_queued(p) || current == p))
> +		else if (p && unlikely(current == p ||
> +			 (task_on_rq_queued(p) && !p->se.sched_delayed)))
>   			lsub_positive(&util_est, _task_util_est(p));
>   
>   		util = max(util, util_est);

Have you tested the above changes to make sure util_est enqueue dequeue 
are balanced? util_est was broken for quite a while when merging delayed 
dequeue because now enqueue_ and dequeue_task() do not always appear in 
pairs. Since then, I always have a local patch like this (may be a bit 
out of date now) to make sure util_est is balanced

https://lore.kernel.org/all/752ae417c02b9277ca3ec18893747c54dd5f277f.1724245193.git.hongyan.xia2@arm.com/