Hi, Ridong,
On Sat, 22 Nov 2025 09:33:34, Chen Ridong wrote:
>On 2025/11/21 18:32, Sun Shaojie wrote:
>> Hi, Ridong,
>>
>> On Thu, 20 Nov 2025 21:45:16, Chen Ridong wrote:
>>> On 2025/11/20 21:07, Sun Shaojie wrote:
>>>> I have carefully considered the scenario where parent effective CPUs are
>>>> empty, which corresponds to the following two cases. (After apply this
>>>> patch).
>>>>
>>>> root cgroup
>>>> |
>>>> A1
>>>> / \
>>>> A2 A3
>>>>
>>>> Case 1:
>>>> Step:
>>>> #1> echo "0-1" > A1/cpuset.cpus
>>>> #2> echo "root" > A1/cpuset.cpus.partition
>>>> #3> echo "0-1" > A2/cpuset.cpus
>>>> #4> echo "root" > A2/cpuset.cpus.partition
>>>>
>>>> After step #4,
>>>>
>>>> | A1 | A2 | A3 |
>>>> cpus_allowed | 0-1 | 0-1 | |
>>>> effective_cpus | | 0-1 | |
>>>> prstate | root | root | member |
>>>>
>>>> After step #4, A3's effective CPUs is empty.
>>>>
>>>
>>> That may be a corner case is unexpected.
>>>
>>>> #5> echo "0-1" > A3/cpuset.cpus
>>>>
>>>
>>> If we create subdirectories (e.g., A4, A5, ...) under the A1 cpuset and
>>> then configure cpuset.cpus
>>> for A1 (a common usage scenario), processes can no longer be migrated into
>>> these subdirectories (A4,
>>> A5, ...) afterward. However, prior to your patch, this migration was
>>> allowed.
>>
>> Are you referring to creating subdirectories (A4, A5, ...) after step #4?
>> And what parameters should be configured for A1's cpuset.cpus?
>> Could you provide a specific example?
>>
>
> #1> echo "0-1" > A1/cpuset.cpus
> #2> echo "root" > A1/cpuset.cpus.partition
> #3> echo "0-1" > A2/cpuset.cpus
> #4> echo "root" > A2/cpuset.cpus.partition
> mkdir A4
> mkdir A5
> echo "0" > A4/cpuset.cpus
> echo $$ > A4/cgroup.procs
> echo "1" > A5/cpuset.cpus
> echo $$ > A5/cgroup.procs
>
>You might be going to argue that we haven't set the cpus for A4/A5..., yeah,
>maybe a corner case.
>
>However, it’s common practice to configure a cpuset’s cpus first and then
>migrate processes—this is
>a typical usage scenario.
>
I'm sorry, I didn't quite understand the point you were trying to make with
this example.
If that's the case
root cgroup
|
A1
/ / \ \
A2 A3 A4 A5
#1> echo "0-1" > A1/cpuset.cpus
#2> echo "root" > A1/cpuset.cpus.partition
#3> echo "0-1" > A2/cpuset.cpus
#4> echo "root" > A2/cpuset.cpus.partition
mkdir A4
mkdir A5
echo "0" > A4/cpuset.cpus
echo $$ > A4/cgroup.procs ->This will return an error because A4's effective
CPUs are empty.
echo "1" > A5/cpuset.cpus
echo $$ > A5/cgroup.procs ->This will return an error because A5's effective
CPUs are empty.
Even with this patch applied, this result will not change.
>
>> Additionally, processes cannot be migrated into a cgroup whose
>> cpuset.cpus.effective is empty. However, this patch does not modify this
>> behavior.
>>
>> So why does applying this patch enable such migration?
Thanks,
Sun Shaojie
