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Sender: Tejun Heo <htejun@gmail.com>
Date:   Sat, 26 Jun 2021 05:57:28 -0400
From:   Tejun Heo <tj@kernel.org>
To:     Josh Don <joshdon@google.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Paul Turner <pjt@google.com>,
        David Rientjes <rientjes@google.com>,
        Oleg Rombakh <olegrom@google.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Steve Sistare <steven.sistare@oracle.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH] sched: cgroup SCHED_IDLE support
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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