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From:   Josh Don <joshdon@google.com>
Date:   Thu, 10 Jun 2021 12:14:57 -0700
Message-ID: <CABk29Nu=mxz3tugjhDV9xCF7DRsMi9U747H+BqubviEva36RUw@mail.gmail.com>
Subject: Re: [PATCH] sched: cgroup SCHED_IDLE support
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        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>,
        Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org
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Precedence: bulk

Hey Dietmar,

On Thu, Jun 10, 2021 at 5:53 AM Dietmar Eggemann
<dietmar.eggemann@arm.com> wrote:
>
> Any reason why this should only work on cgroup-v2?

My (perhaps incorrect) assumption that new development should not
extend v1. I'd actually prefer making this work on v1 as well; I'll
add that support.

> struct cftype cpu_legacy_files[] vs. cpu_files[]
>
> [...]
>
> > @@ -11340,10 +11408,14 @@ void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
> >
> >  static DEFINE_MUTEX(shares_mutex);
> >
> > -int sched_group_set_shares(struct task_group *tg, unsigned long shares)
> > +#define IDLE_WEIGHT sched_prio_to_weight[ARRAY_SIZE(sched_prio_to_weight) - 1]
>
> Why not 3 ? Like for tasks (WEIGHT_IDLEPRIO)?
>
> [...]

Went back and forth on this; on second look, I do think it makes sense
to use the IDLEPRIO weight of 3 here. This gets converted to a 0,
rather than a 1 for display of cpu.weight, which is also actually a
nice property.