Message-ID: <c111762e29004c7d9d39d96387035c89@BJMBX02.spreadtrum.com>
Date:   Thu, 5 Nov 2020 12:50:10 +0000
From:   闫学文 (Xuewen Yan) <Xuewen.Yan@...soc.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
CC:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        "Daniel Bristot de Oliveira" <bristot@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "xuewen.yan94@...il.com" <xuewen.yan94@...il.com>
Subject: 答复: [PATCH v2] sched: revise the initial value of the util_avg.

Hi,Vincent,

At first, I think "sa->util_avg  = cfs_rq->avg.util_avg * se_weight(se)" should
apply to all classes, but I am not sure how this modification would affect other classes.
so I added this cfs condition.

As you said, this is meaningless for this else keeps using se->load.weight.

Thanks!


________________________________________
发件人: Vincent Guittot <vincent.guittot@...aro.org>
发送时间: 2020年11月5日 20:30
收件人: 闫学文 (Xuewen Yan)
抄送: Ingo Molnar; Peter Zijlstra; Juri Lelli; Dietmar Eggemann; Steven Rostedt; Ben Segall; Mel Gorman; Daniel Bristot de Oliveira; linux-kernel; xuewen.yan94@...il.com
主题: Re: [PATCH v2] sched: revise the initial value of the util_avg.

On Thu, 5 Nov 2020 at 12:22, Xuewen Yan <xuewen.yan@...soc.com> wrote:
>
> According to the original code logic:
>                 cfs_rq->avg.util_avg
> sa->util_avg  = -------------------- * se->load.weight
>                 cfs_rq->avg.load_avg

this should have been scale_load_down(se->load.weight) from the beginning

> but for fair_sched_class:
> se->load.weight = 1024 * sched_prio_to_weight[prio];

This is only true for 64bits platform otherwise scale_load and
scale_load_down are nop

>         cfs_rq->avg.util_avg
> so the  -------------------- must be extremely small, the
>         cfs_rq->avg.load_avg
> judgment condition "sa->util_avg < cap" could be established.
> It's not fair for those tasks who has smaller nice value.
>
> Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
> ---
>  kernel/sched/fair.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 290f9e3..079760b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -794,7 +794,11 @@ void post_init_entity_util_avg(struct task_struct *p)
>
>         if (cap > 0) {
>                 if (cfs_rq->avg.util_avg != 0) {

We should now use cpu_util() instead of cfs_rq->avg.util_avg which
takes into account other classes

> -                       sa->util_avg  = cfs_rq->avg.util_avg * se->load.weight;
> +                       if (p->sched_class == &fair_sched_class)
> +                               sa->util_avg  = cfs_rq->avg.util_avg * se_weight(se);
> +                       else
> +                               sa->util_avg  = cfs_rq->avg.util_avg * se->load.weight;

Why this else keeps using se->load.weight ?

Either we uses sa->util_avg  = cfs_rq->avg.util_avg * se_weight(se);
for all classes

Or we want a different init value for other classes. But in this case
se->load.weight is meaningless and we should simply set them to 0
although we could probably compute a value based on bandwidth for
deadline class

> +
>                         sa->util_avg /= (cfs_rq->avg.load_avg + 1);
>
>                         if (sa->util_avg > cap)
> --
> 1.9.1
>
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 This email (including its attachments) is intended only for the person or entity to which it is addressed and may contain information that is privileged, confidential or otherwise protected from disclosure. Unauthorized use, dissemination, distribution or copying of this email or the information herein or taking any action in reliance on the contents of this email or the information herein, by anyone other than the intended recipient, or an employee or agent responsible for delivering the message to the intended recipient, is strictly prohibited. If you are not the intended recipient, please do not read, copy, use or disclose any part of this e-mail to others. Please notify the sender immediately and permanently delete this e-mail and any attachments if you received it in error. Internet communications cannot be guaranteed to be timely, secure, error-free or virus-free. The sender does not accept liability for any errors or omissions.
本邮件及其附件具有保密性质，受法律保护不得泄露，仅发送给本邮件所指特定收件人。严禁非经授权使用、宣传、发布或复制本邮件或其内容。若非该特定收件人，请勿阅读、复制、 使用或披露本邮件的任何内容。若误收本邮件，请从系统中永久性删除本邮件及所有附件，并以回复邮件的方式即刻告知发件人。无法保证互联网通信及时、安全、无误或防毒。发件人对任何错漏均不承担责任。

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