linux-kernel - Re: [PATCH v1] cpuset: Avoid unnecessary partition invalidation

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Message-ID: <b9dce00a-4728-4ac8-ae38-7f41114c7c81@redhat.com>
Date: Tue, 11 Nov 2025 23:09:29 -0500
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>,
 Sun Shaojie <sunshaojie@...inos.cn>
Cc: tj@...nel.org, hannes@...xchg.org, mkoutny@...e.com, shuah@...nel.org,
 cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v1] cpuset: Avoid unnecessary partition invalidation

On 11/11/25 10:33 PM, Chen Ridong wrote:
>
> On 2025/11/12 10:11, Sun Shaojie wrote:
> Hello Shaojie,
>
>> Currently, when a non-exclusive cpuset's "cpuset.cpus" overlaps with a
>> partitioned sibling, the sibling's partition state becomes invalid.
>> However, this invalidation is often unnecessary.
>>
>> This can be observed in specific configuration sequences:
>>
>> Case 1: Partition created first, then non-exclusive cpuset overlaps
>>   #1> mkdir -p /sys/fs/cgroup/A1
>>   #2> echo "0-1" > /sys/fs/cgroup/A1/cpuset.cpus
>>   #3> echo "root" > /sys/fs/cgroup/A1/cpuset.cpus.partition
>>   #4> mkdir -p /sys/fs/cgroup/B1
>>   #5> echo "0-3" > /sys/fs/cgroup/B1/cpuset.cpus
>>   // A1's partition becomes "root invalid" - this is unnecessary
>>
>> Case 2: Non-exclusive cpuset exists first, then partition created
>>   #1> mkdir -p /sys/fs/cgroup/B1
>>   #2> echo "0-1" > /sys/fs/cgroup/B1/cpuset.cpus
>>   #3> mkdir -p /sys/fs/cgroup/A1
>>   #4> echo "0-1" > /sys/fs/cgroup/A1/cpuset.cpus
>>   #5> echo "root" > /sys/fs/cgroup/A1/cpuset.cpus.partition
>>   // A1's partition becomes "root invalid" - this is unnecessary
>>
>> In Case 1, the effective CPU mask of B1 can differ from its requested
>> mask. B1 can use CPUs 2-3 which don't overlap with A1's exclusive
>> CPUs (0-1), thus not violating A1's exclusivity requirement.
>>
>> In Case 2, B1 can inherit the effective CPUs from its parent, so there
>> is no need to invalidate A1's partition state.
>>
>> This patch relaxes the overlap check to only consider conflicts between
>> partitioned siblings, not between a partitioned cpuset and a regular
>> non-exclusive one.
>>
> Does this rule have any negative impact on your products?
>
> The CPUs specified by the user (including cpuset.cpus and cpuset.cpus.exclusive) can be treated as
> the dedicated exclusive CPUs for the partition. For the cases you provided, both siblings can be
> partitions. For example, in case 1, A1 can also be converted to a partition. If this rule is
> relaxed, I don’t see any check for exclusive conflicts when A1 becomes a partition.
>
> Additionally, I think we should preserve the CPU affinity as the user intends as much as possible.

Where does the original patch sent to? I didn't see it.

Anyway it is late for me. I will take a further look tomorrow.

Cheers,
Longman