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

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Message-ID: <YNb6CL6Q9CJnbB2R@mtj.duckdns.org>
Date:   Sat, 26 Jun 2021 05:57:28 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Josh Don <joshdon@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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 <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH] sched: cgroup SCHED_IDLE support

Hello,

On Wed, Jun 16, 2021 at 06:01:59PM -0700, Josh Don wrote:
> Consider a tree like
> 
>                   root
>              /             \
>             A              C
>         /      \             |
>       B       idle       t4
>      |           |     \
>      t1         t2   t3
> 
> Here, 'idle' is our cpu.idle cgroup. The following properties would
> not be possible if we moved t2/t3 into SCHED_IDLE without the cgroup
> interface:
> - t1 always preempts t2/t3 on wakeup, but t4 does not
> - t2 and t3 have different, non-minimum weights. Technically we could
> also achieve this by adding another layer of nested cgroups, but that
> starts to make the hierarchy much more complex.
> - I've also discussed with Peter a possible extension (vruntime
> adjustments) to the current SCHED_IDLE semantics. Similarly to the
> first bullet here, we'd need a cgroup idle toggle to achieve certain
> scheduling behaviors with this.

Would you care to share some concrete use cases?

Thank you.

-- 
tejun