linux-kernel - Re: [PATCH] sched/core: Fix cpu controller for !RT_GROUP

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Date:   Wed, 19 Jun 2019 11:29:05 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     peterz@...radead.org, mingo@...hat.com, rostedt@...dmis.org,
        lizefan@...wei.com, tj@...nel.org, bristot@...hat.com,
        luca.abeni@...tannapisa.it, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/core: Fix cpu controller for !RT_GROUP_SCHED

On Wed, Jun 05, 2019 at 04:20:03PM +0200, Michal Koutný <mkoutny@...e.com> wrote:
> I considered relaxing the check to non-root cgroups only, however, as
> your example shows, it doesn't prevent reaching the avoided state by
> other paths. I'm not that familiar with RT sched to tell whether
> RT-priority tasks in different task_groups break any assumptions.
So I had another look and the check is bogus.

The RT sched with !CONFIG_RT_GROUP_SCHED works only with the struct
rt_rq embedded in the generic struct rq -- regardless of the task's
membership in the cpu controller hierarchy.

Perhaps, the commit message may mention this also prevents enabling cpu
controller on unified hierarchy (if there are any (kernel) RT tasks to
migrate).

Reviewed-by: Michal Koutný <mkoutny@...e.com>