linux-kernel - Re: [RFCv4 PATCH 11/34] sched: Remove blocked load and utilization contributions of dying tasks

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Date:	Tue, 12 May 2015 17:33:22 -0700
From:	Sai Gurrappadi <sgurrappadi@...dia.com>
To:	Morten Rasmussen <morten.rasmussen@....com>,
	<peterz@...radead.org>, <mingo@...hat.com>
CC:	<vincent.guittot@...aro.org>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	<yuyang.du@...el.com>, <preeti@...ux.vnet.ibm.com>,
	<mturquette@...aro.org>, <rjw@...ysocki.net>,
	Juri Lelli <Juri.Lelli@....com>, <pang.xunlei@....com.cn>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	Peter Boonstoppel <pboonstoppel@...dia.com>
Subject: Re: [RFCv4 PATCH 11/34] sched: Remove blocked load and utilization
 contributions of dying tasks

On 05/12/2015 12:38 PM, Morten Rasmussen wrote:
> Task being dequeued for the last time (state == TASK_DEAD) are dequeued
> with the DEQUEUE_SLEEP flag which causes their load and utilization
> contributions to be added to the runqueue blocked load and utilization.
> Hence they will contain load or utilization that is gone away. The issue
> only exists for the root cfs_rq as cgroup_exit() doesn't set
> DEQUEUE_SLEEP for task group exits.
> 
> If runnable+blocked load is to be used as a better estimate for cpu
> load the dead task contributions need to be removed to prevent
> load_balance() (idle_balance() in particular) from over-estimating the
> cpu load.
> 
> cc: Ingo Molnar <mingo@...hat.com>
> cc: Peter Zijlstra <peterz@...radead.org>
> 
> Signed-off-by: Morten Rasmussen <morten.rasmussen@....com>
> ---
>  kernel/sched/fair.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e40cd88..d045404 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3202,6 +3202,8 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  	 * Update run-time statistics of the 'current'.
>  	 */
>  	update_curr(cfs_rq);
> +	if (entity_is_task(se) && task_of(se)->state == TASK_DEAD)
> +		flags &= !DEQUEUE_SLEEP;
>  	dequeue_entity_load_avg(cfs_rq, se, flags & DEQUEUE_SLEEP);
>  
>  	update_stats_dequeue(cfs_rq, se);
> 

Maybe you could use the sched_class->task_dead() callback instead? I
remember seeing a patch from Yuyang that did that.
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