linux-kernel - Re: [PATCH -next RFC 01/16] cpuset: use update_partition_sd_lb in update_cpumasks

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Message-ID: <c40f7e09-3262-4de3-86e6-31a4a6a5338f@redhat.com>
Date: Sun, 19 Oct 2025 22:37:43 -0400
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.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 01/16] cpuset: use update_partition_sd_lb in
 update_cpumasks_hier

On 9/28/25 3:12 AM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@...wei.com>
>
> For cgroup v2, when a cpuset is not a valid partition root, it inherits
> the CS_SCHED_LOAD_BALANCE flag from its parent. The existing logic in
> update_cpumasks_hier() manually handled this inheritance condition.
>
> This patch replaces the inline implementation with a call to the dedicated
> update_partition_sd_lb() helper function, which already encapsulates the
> same logic. The helper function comprehensively handles both the load
> balance flag update and the necessary scheduling domain rebuild decision.
>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
>   kernel/cgroup/cpuset.c | 16 +++-------------
>   1 file changed, 3 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 52468d2c178a..052f9e0c7a65 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1257,6 +1257,8 @@ static void update_partition_sd_lb(struct cpuset *cs, int old_prs)
>   	bool rebuild_domains = (new_prs > 0) || (old_prs > 0);
>   	bool new_lb;
>   
> +	if (!cpuset_v2())
> +		return;
>   	/*
>   	 * If cs is not a valid partition root, the load balance state
>   	 * will follow its parent.
> @@ -2276,19 +2278,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
>   			!cpumask_equal(cp->cpus_allowed, cp->effective_cpus));
>   
>   		cpuset_update_tasks_cpumask(cp, cp->effective_cpus);
> -
> -		/*
> -		 * On default hierarchy, inherit the CS_SCHED_LOAD_BALANCE
> -		 * from parent if current cpuset isn't a valid partition root
> -		 * and their load balance states differ.
> -		 */
> -		if (cpuset_v2() && !is_partition_valid(cp) &&
> -		    (is_sched_load_balance(parent) != is_sched_load_balance(cp))) {
> -			if (is_sched_load_balance(parent))
> -				set_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
> -			else
> -				clear_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
> -		}
> +		update_partition_sd_lb(cp, old_prs);
>   
>   		/*
>   		 * On legacy hierarchy, if the effective cpumask of any non-
Calling update_partition_sd_lb() directly from update_cpumasks_hier() 
may incorrectly force rebuidling sched domain when it is not really 
necessary.

Cheers,
Longman