linux-kernel - Re: [RFC PATCH v4 1/2] sched/fair: Introduce short duration task check

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Date:   Thu, 5 Jan 2023 12:33:16 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Chen Yu <yu.c.chen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Tim Chen <tim.c.chen@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>
Cc:     Juri Lelli <juri.lelli@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Aaron Lu <aaron.lu@...el.com>,
        Abel Wu <wuyun.abel@...edance.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Yicong Yang <yangyicong@...ilicon.com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Hillf Danton <hdanton@...a.com>,
        Honglei Wang <wanghonglei@...ichuxing.com>,
        Len Brown <len.brown@...el.com>,
        Chen Yu <yu.chen.surf@...il.com>,
        Tianchen Ding <dtcccc@...ux.alibaba.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Don <joshdon@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v4 1/2] sched/fair: Introduce short duration task
 check

On 16/12/2022 07:11, Chen Yu wrote:

[...]

> @@ -5995,6 +6005,18 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>  
>  static void set_next_buddy(struct sched_entity *se);
>  
> +static inline void dur_avg_update(struct task_struct *p, bool task_sleep)
> +{
> +	u64 dur;
> +
> +	if (!task_sleep)
> +		return;
> +
> +	dur = p->se.sum_exec_runtime - p->se.prev_sum_exec_runtime_vol;
> +	p->se.prev_sum_exec_runtime_vol = p->se.sum_exec_runtime;

Shouldn't se->prev_sum_exec_runtime_vol be set in enqueue_task_fair()
and not in dequeue_task_fair()->dur_avg_update()? Otherwise `dur` will
contain sleep time.

Like we do for se->prev_sum_exec_runtime in set_next_entity() but for
one `set_next_entity()-put_prev_entity()` run section.

AFAICS, you want to measure the exec_runtime sum over all run sections
between enqueue and dequeue.

> +	update_avg(&p->se.dur_avg, dur);
> +}
> +

[...]