Re: [PATCH] sched/core: Report failed rt migrations to non-root cgroup without rt bandwidth under RT_GROUP_SCHED

[Aaron Tomlin]

On Tue, Sep 16, 2025 at 05:44:14PM +0200, Michal Koutný wrote:
> On Tue, Sep 16, 2025 at 10:47:56AM -0400, Aaron Tomlin <atomlin@xxxxxxxxxxx> wrote:
> > I would prefer not to take any action. However, is there a strong
> > preference to demote the rt task so the CPU controller can be enabled in
> > this context?
> 
> Maybe more context clarifies. The preference is not to end up in this
> corner.

I see. If I understand correctly, in this context, are you suggesting to
modify the identified task's scheduling class (e.g. to SCHED_NORMAL) so the
CPU controller can be enabled?

> I wonder does this combination come from a distro or is it your custom
> setup? I assume the latter (but I'm curious if there's such a distro), in
> that case you likely want to have the cpu controller on v1 hierarchy. v1
> usage is what the boottime switch is currently useful for, v2 de facto
> doesn't support RT group scheduling as of today [1], v2 systems should
> simply unset CONFIG_RT_GROUP_SCHED to avoid issues enabling cpu
> controller.

Yes. Under Red Hat Enterprise Linux (RHEL) 9 Kconfig option
CONFIG_RT_GROUP_SCHED and Cgroup version 2 is enabled by default.
Albeit, upstream can disable SCHED_FIFO/SCHED_RT group scheduling at
boot-time via rt_group_sched=.

> HTH,
> Michal
> 
> [1] This [2] didn't make it into tree thus I'd be reserved with the
>     message printed in your patch too.
> [2] https://lore.kernel.org/all/20250310170442.504716-11-mkoutny@xxxxxxxx/

I see. Understood.


Kind regards,
-- 
Aaron Tomlin