linux-kernel - Re: [PATCH] sched/rt: Don't reschedule a throttled task even if it's higher priority

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Message-ID: <CAJWu+ora8F0eurnYkSXRqcT4mB8k8wy9CyKj1EGk52vEVEkT3A@mail.gmail.com>
Date:   Tue, 30 Nov 2021 18:36:52 -0500
From:   Joel Fernandes <joelaf@...gle.com>
To:     Doug Anderson <dianders@...omium.org>,
        Qais Yousef <qais.yousef@....com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/rt: Don't reschedule a throttled task even if it's
 higher priority

On Tue, Nov 30, 2021 at 11:30 AM Doug Anderson <dianders@...omium.org> wrote:
> I know this isn't crazy urgent and I'm happy to sit and twiddle my
> thumbs a bit longer if everyone is still sleepy from tryptophan, but
> I'm curious if anyone had a chance to look at this. Can anyone confirm
> that my script reproduces for them on something other than my system?

Maybe +Qais Yousef can also chime in. Just to add, I think Doug's
issue is that under RT group scheduling, he expects *other* well
behaved RT tasks to not be throttled while the tasks that are
misbehaving to be *gracefully* throttled. Gracefully being- it is
probably WAI that they are exceeding their runtime and so *should
naturally* be bandwidth-limited similar to deadline. I am not sure if
the design of RT throttling considers throttling as an anomaly or
something that's expected to happen. If it is expected to happen, then
I see Doug's point that the mechanism shouldn't affect other RT tasks.

> Does my patch seem sane?

To be honest, I don't understand that bit enough :(

 -Joel