linux-kernel - Re: [PATCH RFC v2 06/22] cpuset: introduce partition

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Message-ID: <34aae8cd-fc41-46ef-875f-84d0cdafeca7@huaweicloud.com>
Date: Thu, 13 Nov 2025 15:22:42 +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 RFC v2 06/22] cpuset: introduce partition_update()



On 2025/11/13 4:58, Waiman Long wrote:
> On 10/25/25 2:48 AM, Chen Ridong wrote:
>> From: Chen Ridong <chenridong@...wei.com>
>>
>> Introduce partition_update() to centralize updates to key cpuset structures
>> during a partition update, including:
>> - effective_xcpus
>> - exclusive_cpus
>>
>> Key operations performed:
>> - Adding and removing exclusive CPUs via partition_xcpus_add()/del()
>> - Synchronizing the effective exclusive CPUs mask
>> - Updating the exclusive CPUs mask when modification is required
>> - Triggering necessary system updates and workqueue synchronization
>> - Updating the partition's exclusive flag
>> - Sending partition change notifications
>>
>> Signed-off-by: Chen Ridong <chenridong@...wei.com>
>> ---
>>   kernel/cgroup/cpuset.c | 47 ++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 47 insertions(+)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 4a79db1cdec1..3e414e19ae31 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -1604,6 +1604,53 @@ static void partition_disable(struct cpuset *cs, struct cpuset *parent,
>>       notify_partition_change(cs, old_prs);
>>   }
>>   +/**
>> + * partition_update - Update an existing partition configuration
>> + * @cs: The cpuset to update
>> + * @prs: Partition root state (must be positive)
>> + * @xcpus: New exclusive CPUs mask for the partition (NULL to keep current)
>> + * @excpus: New effective exclusive CPUs mask
>> + * @tmp: Temporary masks
>> + *
>> + * Updates partition-related fields. The tmp->addmask is the CPU mask that
>> + * will be added to the subpartitions_cpus and removed from parent's
>> + * effective_cpus, and the tmp->delmask vice versa.
>> + */
>> +static void partition_update(struct cpuset *cs, int prs, struct cpumask *xcpus,
>> +                  struct cpumask *excpus, struct tmpmasks *tmp)
>> +{
>> +    bool isolcpus_updated;
>> +    bool excl_updated;
>> +    struct cpuset *parent;
>> +    int old_prs;
>> +
>> +    lockdep_assert_held(&cpuset_mutex);
>> +    WARN_ON_ONCE(!cpuset_v2());
>> +    WARN_ON_ONCE(prs <= 0);
>> +
>> +    parent = is_remote_partition(cs) ? NULL : parent_cs(cs);
>> +    old_prs = cs->partition_root_state;
>> +    excl_updated = !cpumask_empty(tmp->addmask) ||
>> +               !cpumask_empty(tmp->delmask);
> Should partition_update() only be called if at least one of addmask/delmask is not empty? If they
> are both empty, no update is really needed. Right?

Right, it can return directly.

>> +
>> +    spin_lock_irq(&callback_lock);
>> +    isolcpus_updated = partition_xcpus_add(prs, parent, tmp->addmask);
>> +    isolcpus_updated |= partition_xcpus_del(prs, parent, tmp->delmask);
> 
> I see now that there is no adding and deleting boolean flags to indicate if the cpumasks are empty
> or not, so you have to add the empty cpumask check in those helpers. Please state that in your patch 2.
> 

Will update.

>> +    /*
>> +     * Need to update effective_xcpus and exclusive_cpus now as
>> +     * update_sibling_cpumasks() below may iterate back to the same cs.
>> +     */
>> +    cpumask_copy(cs->effective_xcpus, excpus);
>> +    if (xcpus)
>> +        cpumask_copy(cs->exclusive_cpus, xcpus);
>> +    spin_unlock_irq(&callback_lock);
>> +    update_unbound_workqueue_cpumask(isolcpus_updated);
>> +    if (excl_updated)
>> +        cpuset_force_rebuild();
>> +    update_partition_exclusive_flag(cs, prs);
>> +    notify_partition_change(cs, old_prs);
>> +}
>> +
>>   /*
>>    * prstate_housekeeping_conflict - check for partition & housekeeping conflicts
>>    * @prstate: partition root state to be checked
> 

-- 
Best regards,
Ridong