linux-kernel - Re: [RFC PATCH] sched/fair: Choose the CPU where short task is running during wake up

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Message-ID: <YyRiZTTi2KQfJebc@hirez.programming.kicks-ass.net>
Date:   Fri, 16 Sep 2022 13:47:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     Vincent Guittot <vincent.guittot@...aro.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>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched/fair: Choose the CPU where short task is
 running during wake up

On Fri, Sep 16, 2022 at 12:54:07AM +0800, Chen Yu wrote:

> Current proposal is a variant of 2:
> If the target CPU is running a short-time slice task, and the wakee
> is also a short-time slice task, the target CPU could be chosen as the
> candidate when the system is busy.

Since this benchmark only has short running tasks, the result is that
you always pick the local cpu and therefore the migrations are reduced?

Doesn't this inhibit spreading the workload when there's geniunely idle
CPUs around?