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

[Guopeng Zhang <guopeng.zhang@linux.dev>]

在 2026/9/21 14:38, Ridong Chen 写道:
> 
> 
> 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?
> 

Thanks for the suggestion. I agree that a simple diagram would make this easier to understand.

I'll add the diagrams in v2.

Thanks,
Guopeng