linux-kernel - Re: [PATCH -next RFC 09/11] cpuset: refactor partition_cpus

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Message-ID: <2a6759fa-841a-4185-ae94-b8215c93daf5@redhat.com>
Date: Tue, 2 Sep 2025 09:30:17 -0400
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>, Waiman Long <llong@...hat.com>,
 tj@...nel.org, hannes@...xchg.org, mkoutny@...e.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH -next RFC 09/11] cpuset: refactor partition_cpus_change

On 8/29/25 10:01 PM, Chen Ridong wrote:
>
> On 2025/8/30 4:32, Waiman Long wrote:
>> On 8/28/25 8:56 AM, Chen Ridong wrote:
>>> From: Chen Ridong <chenridong@...wei.com>
>>>
>>> Refactor the partition_cpus_change function to handle both regular CPU
>>> set updates and exclusive CPU modifications, either of which may trigger
>>> partition state changes. This generalized function will also be utilized
>>> for exclusive CPU updates in subsequent patches.
>>>
>>> Signed-off-by: Chen Ridong <chenridong@...wei.com>
>>> ---
>>>    kernel/cgroup/cpuset.c | 59 ++++++++++++++++++++++++++----------------
>>>    1 file changed, 36 insertions(+), 23 deletions(-)
>>>
>>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>>> index 75ad18ab40ae..e3eb87a33b12 100644
>>> --- a/kernel/cgroup/cpuset.c
>>> +++ b/kernel/cgroup/cpuset.c
>>> @@ -2447,6 +2447,41 @@ static int acpus_validate_change(struct cpuset *cs, struct cpuset *trialcs,
>>>        return retval;
>>>    }
>>>    +/**
>>> + * partition_cpus_change - Handle partition state changes due to CPU mask updates
>>> + * @cs: The target cpuset being modified
>>> + * @trialcs: The trial cpuset containing proposed configuration changes
>>> + * @tmp: Temporary masks for intermediate calculations
>>> + *
>>> + * This function handles partition state transitions triggered by CPU mask changes.
>>> + * CPU modifications may cause a partition to be disabled or require state updates.
>>> + */
>>> +static void partition_cpus_change(struct cpuset *cs, struct cpuset *trialcs,
>>> +                    struct tmpmasks *tmp)
>>> +{
>>> +    if (cs_is_member(cs))
>>> +        return;
>>> +
>>> +    invalidate_cs_partition(trialcs);
>>> +    if (trialcs->prs_err)
>>> +        cs->prs_err = trialcs->prs_err;
>>> +
>>> +    if (is_remote_partition(cs)) {
>>> +        if (trialcs->prs_err)
>>> +            remote_partition_disable(cs, tmp);
>>> +        else
>>> +            remote_cpus_update(cs, trialcs->exclusive_cpus,
>>> +                       trialcs->effective_xcpus, tmp);
>>> +    } else {
>>> +        if (trialcs->prs_err)
>>> +            update_parent_effective_cpumask(cs, partcmd_invalidate,
>>> +                            NULL, tmp);
>>> +        else
>>> +            update_parent_effective_cpumask(cs, partcmd_update,
>>> +                            trialcs->effective_xcpus, tmp);
>>> +    }
>>> +}
>>> +
>>>    /**
>>>     * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
>>>     * @cs: the cpuset to consider
>>> @@ -2483,29 +2518,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>>>         */
>>>        force = !cpumask_equal(cs->effective_xcpus, trialcs->effective_xcpus);
>>>    -    invalidate_cs_partition(trialcs);
>>> -    if (trialcs->prs_err)
>>> -        cs->prs_err = trialcs->prs_err;
>>> -
>>> -    if (is_partition_valid(cs) ||
>>> -       (is_partition_invalid(cs) && !trialcs->prs_err)) {
>>> -        struct cpumask *xcpus = trialcs->effective_xcpus;
>>> -
>>> -        if (cpumask_empty(xcpus) && is_partition_invalid(cs))
>>> -            xcpus = trialcs->cpus_allowed;
>> This if statement was added in commit 46c521bac592 ("cgroup/cpuset: Enable invalid to valid local
>> partition transition") that is missing in your new partition_cpus_change() function. Have you run
>> the test_cpuset_prs.sh selftest with a patched kernel to make sure that there is no test failure?
>>
>> Cheers,
>> Longman
> Thank you Longman,
>
> I did run the self-test for every patch, and I appreciate the test script test_cpuset_prs.sh you
> provided.
>
> The trialcs->effective_xcpus will be updated using compute_trialcs_excpus, which was introduced in
> Patch 4. The corresponding logic was then added in Patch 5:
>
> -	cpumask_and(excpus, user_xcpus(trialcs), parent->effective_xcpus);
> +	/* trialcs is member, cpuset.cpus has no impact to excpus */
> +	if (cs_is_member(cs))
> +		cpumask_and(excpus, trialcs->exclusive_cpus,
> +				parent->effective_xcpus);
> +	else
> +		cpumask_and(excpus, user_xcpus(trialcs), parent->effective_xcpus);
> +
>
> Therefore, as long as excpus is computed correctly, I believe this implementation can handle the
> scenario appropriately.

It will be helpful to put down a note in the commit log that the missing 
logic will be re-introduced in a subsequent patch.

Thanks,
Longman