linux-kernel - Re: [PATCH v4 1/6] sched/fair: Fix reschedule which is generated on throttled cfs

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Date:	Fri, 24 Oct 2014 07:27:14 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Kirill Tkhai <ktkhai@...allels.com>, linux-kernel@...r.kernel.org
CC:	peterz@...radead.org, pjt@...gle.com, oleg@...hat.com,
	rostedt@...dmis.org, umgwanakikbuti@...il.com, tkhai@...dex.ru,
	tim.c.chen@...ux.intel.com, mingo@...nel.org,
	nicolas.pitre@...aro.org
Subject: Re: [PATCH v4 1/6] sched/fair: Fix reschedule which is generated
 on throttled cfs_rq

Hi Kirill,
8/6/14, 4:06 PM, Kirill Tkhai:
> (sched_entity::on_rq == 1) does not guarantee the task is pickable;
> changes on throttled cfs_rq must not lead to reschedule.

Why (sched_entity::on_rq == 1) doesn't guarantee the task is pickable 
since entity will be dequeued during throttling cfs_rq?

>
> Check for task_struct::on_rq instead.

Do you mean task_struct::on_rq will be cleared during throttling cfs_rq? 
I can't find codes do this.

Regards,
Wanpeng Li

>
> Signed-off-by: Kirill Tkhai <ktkhai@...allels.com>
> ---
>   kernel/sched/fair.c |    6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index bfa3c86..6f0ce2b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7465,7 +7465,7 @@ static void task_fork_fair(struct task_struct *p)
>   static void
>   prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
>   {
> -	if (!p->se.on_rq)
> +	if (!p->on_rq)
>   		return;
>   
>   	/*
> @@ -7521,15 +7521,15 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
>    */
>   static void switched_to_fair(struct rq *rq, struct task_struct *p)
>   {
> -	struct sched_entity *se = &p->se;
>   #ifdef CONFIG_FAIR_GROUP_SCHED
> +	struct sched_entity *se = &p->se;
>   	/*
>   	 * Since the real-depth could have been changed (only FAIR
>   	 * class maintain depth value), reset depth properly.
>   	 */
>   	se->depth = se->parent ? se->parent->depth + 1 : 0;
>   #endif
> -	if (!se->on_rq)
> +	if (!p->on_rq)
>   		return;
>   
>   	/*
>
>
>
> --
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