Re: [PATCH 2/2] docs: cgroup-v2: Describe effective CPUs of partition roots

[Ridong Chen <ridong.chen@linux.dev>]

On 9/18/2026 6:23 PM, Guopeng Zhang wrote:
> From: Guopeng Zhang <zhangguopeng@kylinos.cn>
> 
> The cpuset.cpus.effective description says that the effective CPUs are
> granted by the parent and are normally a subset of cpuset.cpus. This
> does not always hold for a valid non-root partition root. Its effective
> CPUs are the active CPUs in cpuset.cpus.exclusive.effective after CPUs
> assigned to valid child partition roots are removed.
> 
> If cpuset.cpus.exclusive differs from cpuset.cpus, the effective CPUs
> may therefore be outside cpuset.cpus. Remote partitions also do not
> necessarily get their CPUs from their immediate parent.
> 
> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
> ---
>   Documentation/admin-guide/cgroup-v2.rst | 29 ++++++++++++++++---------
>   1 file changed, 19 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 272e9f2432bd..49ce8deb4115 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -2505,16 +2505,25 @@ Cpuset Interface Files
>   	A read-only multiple values file which exists on all
>   	cpuset-enabled cgroups.
>   
> -	It lists the onlined CPUs that are actually granted to this
> -	cgroup by its parent.  These CPUs are allowed to be used by
> -	tasks within the current cgroup.
> -
> -	If "cpuset.cpus" is empty, the "cpuset.cpus.effective" file shows
> -	all the CPUs from the parent cgroup that can be available to
> -	be used by this cgroup.  Otherwise, it should be a subset of
> -	"cpuset.cpus" unless none of the CPUs listed in "cpuset.cpus"
> -	can be granted.  In this case, it will be treated just like an
> -	empty "cpuset.cpus".
> +	It lists the active CPUs available to tasks in this cgroup.
> +
> +	For a cgroup that is not a valid partition root, an empty
> +	"cpuset.cpus" makes "cpuset.cpus.effective" show all CPUs
> +	available from the parent cgroup.  Otherwise, it is a subset
> +	of "cpuset.cpus" unless none of the requested CPUs can be
> +	granted.  In that case, it is treated like an empty
> +	"cpuset.cpus".
> +
> +	For a valid non-root partition root, "cpuset.cpus.effective" contains
> +	the active CPUs from "cpuset.cpus.exclusive.effective" except
> +	those granted to valid child partition roots.  If
> +	"cpuset.cpus.exclusive" is set to a value different from
> +	"cpuset.cpus", the effective CPUs need not be a subset of
> +	"cpuset.cpus".  For example, if CPUs 2-5 are active,
> +	available, and not assigned to a valid child partition root,
> +	a partition root with "cpuset.cpus" set to "0-3" and
> +	"cpuset.cpus.exclusive" set to "2-5" has "2-5" in
> +	"cpuset.cpus.effective".
>   
>   	Its value will be affected by CPU hotplug events.
>   

Hi Guopeng,

Thank you for your effort.

May I suggest adding a simple diagram to help clarify the relationship? 
Similarly, could you add a simple diagram to illustrate the relationship? 
Something like:

```
   A(cpu,memory) - B(memory) - C()
                             \ D()
```

I mean adding one diagram for the valid root case and another for the others 
(member / invalid root), so it becomes easier to see how they differ. What do 
you think?

-- 
Best regards
Ridong