linux-kernel - Re: [PATCH 2/2] sched/core: Uncookied force idle accounting per cpu

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Date:   Tue, 4 Jan 2022 17:56:17 -0800
From:   Josh Don <joshdon@...gle.com>
To:     Cruz Zhao <CruzZhao@...ux.alibaba.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched/core: Uncookied force idle accounting per cpu

Hi Cruz,

On Thu, Dec 23, 2021 at 4:30 AM Cruz Zhao <CruzZhao@...ux.alibaba.com> wrote:
>
> Forced idle can be divided into two types, forced idle with cookie'd task
> running on it SMT sibling, and forced idle with uncookie'd task running
> on it SMT sibling, which should be accounting to measure the cost of
> enabling core scheduling too.
>
> This patch accounts the forced idle time with uncookie'd task, and the
> sum of both.
>
> A few details:
>  - Uncookied forceidle time and total forceidle time is displayed via
>    the last two columns of /proc/stat.
>  - Uncookied forceidle time is ony accounted when this cpu is forced
>    idle and a sibling hyperthread is running with an uncookie'd task.

What is the purpose/use-case to account the forced idle from
uncookie'd tasks? The forced-idle from cookie'd tasks represents
capacity loss due to adding in some cookie'd tasks. If forced idle is
high, that can be rectified by making some changes to the cookie'd
tasks (ie. their affinity, cpu budget, etc.).