Re: [PATCH 1/2] cgroup, docs: Be explicit about independence of RT_GROUP_SCHED and non-cpu controllers

[Waiman Long <llong@redhat.com>]

On 3/4/25 11:12 PM, Shashank Balaji via B4 Relay wrote:
> From: Shashank Balaji <shashank.mahadasyam@sony.com>
>
> The cgroup v2 cpu controller has a limitation that if
> CONFIG_RT_GROUP_SCHED is enabled, the cpu controller can be enabled only
> if all the realtime processes are in the root cgroup. The other
> controllers have no such restriction. They can be used for the resource
> control of realtime processes irrespective of whether
> CONFIG_RT_GROUP_SCHED is enabled or not.
>
> Signed-off-by: Shashank Balaji <shashank.mahadasyam@sony.com>
> ---
>   Documentation/admin-guide/cgroup-v2.rst | 23 ++++++++++++++---------
>   1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index cb1b4e759b7e267c24d7f4f69564c16fb29c4d89..f293a13b42ed69e7c6bf5e974cb86e228411af4e 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1076,15 +1076,20 @@ cpufreq governor about the minimum desired frequency which should always be
>   provided by a CPU, as well as the maximum desired frequency, which should not
>   be exceeded by a CPU.
>   
> -WARNING: cgroup2 doesn't yet support control of realtime processes. For
> -a kernel built with the CONFIG_RT_GROUP_SCHED option enabled for group
> -scheduling of realtime processes, the cpu controller can only be enabled
> -when all RT processes are in the root cgroup.  This limitation does
> -not apply if CONFIG_RT_GROUP_SCHED is disabled.  Be aware that system
> -management software may already have placed RT processes into nonroot
> -cgroups during the system boot process, and these processes may need
> -to be moved to the root cgroup before the cpu controller can be enabled
> -with a CONFIG_RT_GROUP_SCHED enabled kernel.
> +WARNING: cgroup2 cpu controller doesn't yet fully support the control of
> +realtime processes. For a kernel built with the CONFIG_RT_GROUP_SCHED option
> +enabled for group scheduling of realtime processes, the cpu controller can only
> +be enabled when all RT processes are in the root cgroup. Be aware that system
> +management software may already have placed RT processes into non-root cgroups
> +during the system boot process, and these processes may need to be moved to the
> +root cgroup before the cpu controller can be enabled with a
> +CONFIG_RT_GROUP_SCHED enabled kernel.
> +
> +With CONFIG_RT_GROUP_SCHED disabled, this limitation does not apply and some of
> +the interface files either affect realtime processes or account for them. See
> +the following section for details. Only the cpu controller is affected by
> +CONFIG_RT_GROUP_SCHED. Other controllers can be used for the resource control of
> +realtime processes irrespective of CONFIG_RT_GROUP_SCHED.
>   
>   
>   CPU Interface Files

LGTM

Acked-by: Waiman Long <longman@redhat.com>