linux-kernel - Re: [PATCH -next RFC 03/16] cpuset: factor out partition

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Message-ID: <fa7fa2e5-c602-4318-90e1-89c742c6cc1a@huaweicloud.com>
Date: Mon, 20 Oct 2025 15:48:38 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Waiman Long <llong@...hat.com>, tj@...nel.org, hannes@...xchg.org,
 mkoutny@...e.com
Cc: cgups@...r.kernel.org, linux-kernel@...r.kernel.org,
 lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH -next RFC 03/16] cpuset: factor out partition_enable()
 function



On 2025/10/20 10:39, Waiman Long wrote:
> On 9/28/25 3:12 AM, Chen Ridong wrote:
>> From: Chen Ridong <chenridong@...wei.com>
>>
>> Extract the core partition enablement logic into a dedicated
>> partition_enable() function. This refactoring centralizes updates to key
>> cpuset data structures including remote_sibling, effective_xcpus,
>> partition_root_state, and prs_err.
>>
>> The function handles the complete partition enablement workflow:
>> - Adding exclusive CPUs via partition_xcpus_add()
>> - Managing remote sibling relationships
>> - Synchronizing effective exclusive CPUs mask
>> - Updating partition state and error status
>> - Triggering required scheduler domain rebuilds
>>
>> This creates a coherent interface for partition operations and establishes
>> a foundation for future local partition support while maintaining existing
>> remote partition behavior.
>>
>> Signed-off-by: Chen Ridong <chenridong@...wei.com>
>> ---
>>   kernel/cgroup/cpuset.c | 55 +++++++++++++++++++++++++++++++++---------
>>   1 file changed, 44 insertions(+), 11 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 0787904321a9..43ce62f4959c 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -1515,6 +1515,49 @@ static inline bool is_local_partition(struct cpuset *cs)
>>       return is_partition_valid(cs) && !is_remote_partition(cs);
>>   }
>>   +static void partition_state_update(struct cpuset *cs, int new_prs,
>> +                      enum prs_errcode prs_err)
>> +{
>> +    lockdep_assert_held(&callback_lock);
>> +
>> +    cs->partition_root_state = new_prs;
>> +    WRITE_ONCE(cs->prs_err, prs_err);
>> +    if (!is_partition_valid(cs))
>> +        reset_partition_data(cs);
>> +}
>> +
>> +/**
>> + * partition_enable - Transitions a cpuset to a partition root
>> + * @cs: The cpuset to enable partition for
>> + * @parent: Parent cpuset of @cs, NULL for remote parent
>> + * @new_prs: New partition root state to set
>> + * @new_excpus: New exclusive CPUs mask for the partition
>> + *
>> + * Transitions a cpuset to a partition root, only for v2.
>> + */
>> +static void partition_enable(struct cpuset *cs, struct cpuset *parent,
>> +                 int new_prs, struct cpumask *new_excpus)
>> +{
>> +    bool isolcpus_updated;
>> +
>> +    lockdep_assert_held(&cpuset_mutex);
>> +    WARN_ON_ONCE(new_prs <= 0);
>> +    WARN_ON_ONCE(!cpuset_v2());
>> +
>> +    if (cs->partition_root_state == new_prs)
>> +        return;
>> +
>> +    spin_lock_irq(&callback_lock);
>> +    /* enable partition should only add exclusive cpus */
>> +    isolcpus_updated = partition_xcpus_add(new_prs, parent, new_excpus);
>> +    list_add(&cs->remote_sibling, &remote_children);
>> +    cpumask_copy(cs->effective_xcpus, new_excpus);
>> +    partition_state_update(cs, new_prs, PERR_NONE);
>> +    spin_unlock_irq(&callback_lock);
>> +    update_unbound_workqueue_cpumask(isolcpus_updated);
>> +    cpuset_force_rebuild();
>> +}
>> +
> partition_enable() is supposed to be a common helper used for the creation of both local and remote
> partitions. The one in this patch does work for remote partition but not for local partition. I
> would prefer to make it good for both cases when you introduce it instead adding code in patch 6 to
> make it work for local partition later in the series. It will make it easier to review instead of
> jumping back and forth to make sure that it will do the right thing.
> 
> Cheers,
> Longman
> 

Thank you, Longman.

My original intention was to keep the changes easier to review. Patches 3–5 are meant to be pure
refactoring moves of code from the remote partition logic, without altering any behavior.

Would it be clearer to proceed in the following stages:

1. Introduce partition_enable(), partition_disable(), and partition_update() with their complete
logic first.
2. Replace the corresponding logic in remote partitions with these new helpers.
3. Then, replace the logic in local partitions with the same helpers.

-- 
Best regards,
Ridong