linux-kernel - Re: [PATCH] sched: Improve the accuracy of sched_stat

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Date: Tue, 16 Apr 2024 15:13:00 +0800
From: Zhang Qiao <zhangqiao22@...wei.com>
To: <mingo@...hat.com>, <peterz@...radead.org>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
	<bristot@...hat.com>, <vschneid@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <qianjun.kernel@...il.com>,
	<laoar.shao@...il.com>
Subject: Re: [PATCH] sched: Improve the accuracy of sched_stat_wait statistics
 for rt and dl

ping.

在 2024/3/22 16:15, Zhang Qiao 写道:
> Where commit b9c88f752268 ("sched/fair: Improve the accuracy of
> sched_stat_wait statistics") fixed a wrong scenairio for cfs schedstat.
> 
> This wrong scenario is also present for the RT task. For avoiding this
> scenario, add wait_start check in __update_stats_wait_end();
> 
> Signed-off-by: Zhang Qiao <zhangqiao22@...wei.com>
> ---
>  kernel/sched/fair.c  |  9 ---------
>  kernel/sched/stats.c | 11 ++++++++++-
>  2 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 6a16129f9a5c..36c81fe0086b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1208,15 +1208,6 @@ update_stats_wait_end_fair(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  
>  	stats = __schedstats_from_se(se);
>  
> -	/*
> -	 * When the sched_schedstat changes from 0 to 1, some sched se
> -	 * maybe already in the runqueue, the se->statistics.wait_start
> -	 * will be 0.So it will let the delta wrong. We need to avoid this
> -	 * scenario.
> -	 */
> -	if (unlikely(!schedstat_val(stats->wait_start)))
> -		return;
> -
>  	if (entity_is_task(se))
>  		p = task_of(se);
>  
> diff --git a/kernel/sched/stats.c b/kernel/sched/stats.c
> index 857f837f52cb..7077eb490c09 100644
> --- a/kernel/sched/stats.c
> +++ b/kernel/sched/stats.c
> @@ -20,8 +20,17 @@ void __update_stats_wait_start(struct rq *rq, struct task_struct *p,
>  void __update_stats_wait_end(struct rq *rq, struct task_struct *p,
>  			     struct sched_statistics *stats)
>  {
> -	u64 delta = rq_clock(rq) - schedstat_val(stats->wait_start);
> +	u64 delta;
>  
> +	/*
> +	 * When the sched_schedstat changes from 0 to 1, some sched se
> +	 * maybe already in the runqueue, the stats->wait_start will be 0.
> +	 * So it will let the delta wrong. We need to avoid this scenario.
> +	 */
> +	if (unlikely(!schedstat_val(stats->wait_start)))
> +		return;
> +
> +	delta = rq_clock(rq) - schedstat_val(stats->wait_start);
>  	if (p) {
>  		if (task_on_rq_migrating(p)) {
>  			/*
>