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

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Message-ID: <031d83b6-bc67-4941-8c49-e1d12df74062@huaweicloud.com>
Date: Sat, 30 Aug 2025 10:01:34 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: 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 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.

-- 
Best regards,
Ridong