linux-kernel - Re: [PATCH] sched: cgroup SCHED

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Message-ID: <bd6320bb038f02d2bad0bb07ecf2b23f3cda9167.camel@surriel.com>
Date:   Sat, 26 Jun 2021 07:42:27 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>
Cc:     Josh Don <joshdon@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        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>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Paul Turner <pjt@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Oleg Rombakh <olegrom@...gle.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Steve Sistare <steven.sistare@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: cgroup SCHED_IDLE support

On Fri, 2021-06-25 at 10:08 +0200, Peter Zijlstra wrote:
> On Wed, Jun 16, 2021 at 11:42:05AM -0400, Tejun Heo wrote:
> > A high-level problem that I see with the proposal is that this
> > would bake
> > the current recursive implementation into the interface. The
> > semantics of
> > the currently exposed interface, at least the weight based part, is
> > abstract
> > and doesn't necessarily dictate how the scheduling is actually
> > performed.
> > Adding this would mean that we're now codifying the current
> > behavior of
> > fully nested scheduling into the interface.
> 
> It's a direct concequence of the hierarchical requirement. The
> approach
> is the only valid one. The other relative controllers that don't do
> this, are simply broken.
> 
> Absolute controllers have it easier, they can be trivially flattened.

I'm pretty sure CFS can be mostly flattened too, just not
trivially :)

Doing the delta_exectime to vruntime accounting in a somewhat
delayed fashion, with never more than one or two timeslices
worth of vruntime at a time being accounted, should make the
flat CFS runqueue model work.

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