linux-kernel - Re: [RFC PATCH V3 6/6] sched/fair: Implement starvation monitor

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Message-ID: <ZInLcNqGpLCw8xsn@localhost.localdomain>
Date:   Wed, 14 Jun 2023 16:15:12 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vineeth Pillai <vineeth@...byteword.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [RFC PATCH V3 6/6] sched/fair: Implement starvation monitor

Hey,

So Daniel provided the gory details :) .. but please let me highlight
one of his points below, which I think it might clarify why we might
want to start with a special case, patch 6 improved approach, before
possibly moving to more complex implementations.

On 14/06/23 15:45, Daniel Bristot de Oliveira wrote:

...

> By postponing the enqueue/replanishment of the DL server here, we are fixing the
> problem in a practical way, that works without breaking existing useful properties &
> use-cases.

In my understanding, if we simply postpone actual activation of the DL
server up to the point it really needs to boost/run for giving CFS tasks
some breath (the infamous 0-laxity :), we save RT tasks from useless
interruptions and still can keep EDF/CBS working w/o much changes.

It looks like a low hanging fruit, small improvement on what we have today
than doesn't prevent us for implementing more complex features (i.e., full
blown hierarchical scheduling, alternative schedulers) in the future if
the need arises.

Thanks!
Juri