linux-kernel - Re: [PATCH v3 1/2] sched/fair: Introduce short duration task check

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Date:   Tue, 6 Dec 2022 18:23:47 -0800
From:   Josh Don <joshdon@...gle.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        Chen Yu <yu.c.chen@...el.com>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Honglei Wang <wanghonglei@...ichuxing.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        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>,
        Dietmar Eggemann <dietmar.eggemann@....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>,
        Len Brown <len.brown@...el.com>,
        Chen Yu <yu.chen.surf@...il.com>,
        Tianchen Ding <dtcccc@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] sched/fair: Introduce short duration task check

> We don't want to add more dedicated knobs. So using
> sysctl_sched_min_granularity as you are doing in this patch looks ok

If not a knob, then maybe at least a smaller hardcoded value? Several
milliseconds seems like too long for this optimization; the
opportunity cost of not doing the idle search likely doesn't make
sense if the waker is going to be active for several additional
milliseconds. I would have guessed something on the order of 100us.

Chen, what is the run duration of tasks in your ping pong example?