Re: [PATCH] sched: Remove CONFIG_RT_GROUP_SCHED

[Tejun Heo <tj@kernel.org>]

Hello, Sebastian.

On Thu, Nov 05, 2026 at 05:47:24PM +0100, Sebastian Andrzej Siewior wrote:
> The RT_GROUP_SCHED is broken beyond repair and it is to not enable it
> during compile. If enabled it is recommended to disable it at boot time
> with the rt_group_sched= option.
> With it enabled it is not possible to set the policy of a task to
> SCHED_{FIFO|RR} because its cgroup has no runtime assigned. The runtime
> can not be assigned with cgroup v2. The root group has however all the
> runtime assigned meaning the global sysctl runtime parameter
> (sched_rt_runtime_us) can no be reduced because the new bandwidth will
> be less than what is current available.
> It is possible to schedule SCHED_DEADLINE tasks but the admission
> control is stuck can only be disabled via -1 (same sysctl parameter).
> 
> As a result all major distors (Debian, Open Suse, Fedora, Archlinux)
> have it disabled.
> 
> I don't think it is needed to somehow fix RT_GROUP_SCHED. The DL fair
> server already handles the RT throttling mechanism. There is work on
> Hierarchical constant bandwidth server (HCBS) which aim to group
> multiple real-time tasks within one deadline configuration.
> 
> Remove CONFIG_RT_GROUP_SCHED.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

I'm not against it but wonder whether it'd be useful to do it more gradually
so that people can pipe up if they depend on it. ie. Mark it deprecated and
put it behind EXPORT for a bit and then BROKEN before actual removal.

Thanks.

-- 
tejun