linux-kernel - Re: [PATCH -next RFC -v2 09/11] cpuset: refactor partition_cpus

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Message-ID: <3815a523-a6d1-4612-8ec8-b955694a5792@redhat.com>
Date: Mon, 15 Sep 2025 15:34:40 -0400
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.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 -v2 09/11] cpuset: refactor
 partition_cpus_change

On 9/8/25 11:32 PM, 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.
>
> With the introduction of compute_trialcs_excpus in a previous patch,
> the trialcs->effective_xcpus field is now consistently computed and
> maintained. Consequently, the legacy logic which assigned
> **trialcs->allowed_cpus to a local 'xcpus' variable** when
> trialcs->effective_xcpus was empty has been removed.
>
> This removal is safe because when trialcs is not a partition member,
> trialcs->effective_xcpus is now correctly populated with the intersection
> of user_xcpus and the parent's effective_xcpus. This calculation inherently
> covers the scenario previously handled by the removed code.
>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
>   kernel/cgroup/cpuset.c | 66 +++++++++++++++++++++++++-----------------
>   1 file changed, 40 insertions(+), 26 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 6aa93bd9d5dd..de61520f1e44 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -2453,6 +2453,45 @@ static int cpus_allowed_validate_change(struct cpuset *cs, struct cpuset *trialc
>   	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)
> +{
> +	enum prs_errcode prs_err;
> +
> +	if (cs_is_member(cs))
> +		return;
> +
> +	prs_err = validate_partition(cs, trialcs);
> +	if (prs_err) {
> +		trialcs->prs_err = prs_err;
> +		cs->prs_err = prs_err;
> +	}

The assignment can be simplified into

     trialcs->prs_err = cs->prs_err = 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
> @@ -2466,7 +2505,6 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>   	struct tmpmasks tmp;
>   	bool force = false;
>   	int old_prs = cs->partition_root_state;
> -	enum prs_errcode prs_err;
>   
>   	retval = parse_cpuset_cpulist(buf, trialcs->cpus_allowed);
>   	if (retval < 0)
> @@ -2491,31 +2529,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>   	 */
>   	force = !cpumask_equal(cs->effective_xcpus, trialcs->effective_xcpus);
>   
> -	prs_err = validate_partition(cs, trialcs);
> -	if (prs_err) {
> -		trialcs->prs_err = prs_err;
> -		cs->prs_err = 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;
> -
> -		/*
> -		 * Call remote_cpus_update() to handle valid remote partition
> -		 */
> -		if (is_remote_partition(cs))
> -			remote_cpus_update(cs, NULL, xcpus, &tmp);
> -		else if (trialcs->prs_err)
> -			update_parent_effective_cpumask(cs, partcmd_invalidate,
> -							NULL, &tmp);
> -		else
> -			update_parent_effective_cpumask(cs, partcmd_update,
> -							xcpus, &tmp);
> -	}
> +	partition_cpus_change(cs, trialcs, &tmp);
>   
>   	spin_lock_irq(&callback_lock);
>   	cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
Reviewed-by: Waiman Long <longman@...hat.com>