linux-kernel - Re: [PATCH 7/9] sched: Add migrate

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Message-ID: <20200923170809.GY1362448@hirez.programming.kicks-ass.net>
Date:   Wed, 23 Sep 2020 19:08:09 +0200
From:   peterz@...radead.org
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Daniel Bristot de Oliveira <bristot@...hat.com>, mingo@...nel.org,
        linux-kernel@...r.kernel.org, bigeasy@...utronix.de,
        qais.yousef@....com, swood@...hat.com, valentin.schneider@....com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, vincent.donnefort@....com
Subject: Re: [PATCH 7/9] sched: Add migrate_disable()

On Wed, Sep 23, 2020 at 10:31:10AM +0200, Thomas Gleixner wrote:
>    In practice migrate disable could be taken into account on placement
>    decisions, but yes we don't have anything like that at the moment.

I think at the very least we should do some of that.

The premise is wanting to run the M highest priority tasks, when a CPU
drops priority, it tries to PULL a higher priority task towards itself.
If this PULL selects a migrate_disable() tasks, it means the task is in
the M highest prio tasks.

Since obviously that task cannot get pulled, we should then pull the
current running task of that CPU, this would then allow the
migrate_disable() task to resume execution.

I'll go try and cook up something along those lines...