linux-kernel - Re: [PATCH -next 3/3] cgroup/cpuset: remove use_parent

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Message-ID: <ca2721e6-b134-41a1-b303-988ddfe057b1@redhat.com>
Date: Mon, 19 Aug 2024 14:43:07 -0400
From: Waiman Long <longman@...hat.com>
To: Chen Ridong <chenridong@...wei.com>, tj@...nel.org,
 lizefan.x@...edance.com, hannes@...xchg.org, adityakali@...gle.com,
 sergeh@...nel.org, mkoutny@...e.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next 3/3] cgroup/cpuset: remove use_parent_ecpus of
 cpuset

On 8/16/24 04:27, Chen Ridong wrote:
> use_parent_ecpus is used to track whether the children are using the
> parent's effective_cpus. When a parent's effective_cpus is changed
> due to changes in a child partition's effective_xcpus, any child
> using parent'effective_cpus must call update_cpumasks_hier. However,
> if a child is not a valid partition, it is sufficient to determine
> whether to call update_cpumasks_hier based on whether the child's
> effective_cpus is going to change. To make the code more succinct,
> it is suggested to remove use_parent_ecpus.
>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
>   kernel/cgroup/cpuset.c | 30 ++++--------------------------
>   1 file changed, 4 insertions(+), 26 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 8be0259065f5..71c24542966b 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -185,12 +185,6 @@ struct cpuset {
>   	/* partition root state */
>   	int partition_root_state;
>   
> -	/*
> -	 * Default hierarchy only:
> -	 * use_parent_ecpus - set if using parent's effective_cpus
> -	 */
> -	int use_parent_ecpus;
> -
>   	/*
>   	 * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
>   	 * know when to rebuild associated root domain bandwidth information.
> @@ -1505,11 +1499,8 @@ static void reset_partition_data(struct cpuset *cs)
>   		if (is_cpu_exclusive(cs))
>   			clear_bit(CS_CPU_EXCLUSIVE, &cs->flags);
>   	}
> -	if (!cpumask_and(cs->effective_cpus,
> -			 parent->effective_cpus, cs->cpus_allowed)) {
> -		cs->use_parent_ecpus = true;
> +	if (!cpumask_and(cs->effective_cpus, parent->effective_cpus, cs->cpus_allowed))
>   		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
> -	}
>   }
>   
>   /*
> @@ -1683,8 +1674,6 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
>   	spin_lock_irq(&callback_lock);
>   	isolcpus_updated = partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
>   	list_add(&cs->remote_sibling, &remote_children);
> -	if (cs->use_parent_ecpus)
> -		cs->use_parent_ecpus = false;
>   	spin_unlock_irq(&callback_lock);
>   	update_unbound_workqueue_cpumask(isolcpus_updated);
>   
> @@ -2309,13 +2298,8 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
>   		 * it is a partition root that has explicitly distributed
>   		 * out all its CPUs.
>   		 */
> -		if (is_in_v2_mode() && !remote && cpumask_empty(tmp->new_cpus)) {
> +		if (is_in_v2_mode() && !remote && cpumask_empty(tmp->new_cpus))
>   			cpumask_copy(tmp->new_cpus, parent->effective_cpus);
> -			if (!cp->use_parent_ecpus)
> -				cp->use_parent_ecpus = true;
> -		} else if (cp->use_parent_ecpus) {
> -			cp->use_parent_ecpus = false;
> -		}
>   
>   		if (remote)
>   			goto get_css;
> @@ -2452,8 +2436,7 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
>   	 * Check all its siblings and call update_cpumasks_hier()
>   	 * if their effective_cpus will need to be changed.
>   	 *
> -	 * With the addition of effective_xcpus which is a subset of
> -	 * cpus_allowed. It is possible a change in parent's effective_cpus
> +	 * It is possible a change in parent's effective_cpus
>   	 * due to a change in a child partition's effective_xcpus will impact
>   	 * its siblings even if they do not inherit parent's effective_cpus
>   	 * directly.
> @@ -2467,8 +2450,7 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
>   	cpuset_for_each_child(sibling, pos_css, parent) {
>   		if (sibling == cs)
>   			continue;
> -		if (!sibling->use_parent_ecpus &&
> -		    !is_partition_valid(sibling)) {
> +		if (!is_partition_valid(sibling)) {
>   			compute_effective_cpumask(tmp->new_cpus, sibling,
>   						  parent);
>   			if (cpumask_equal(tmp->new_cpus, sibling->effective_cpus))
> @@ -4128,7 +4110,6 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
>   	if (is_in_v2_mode()) {
>   		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
>   		cs->effective_mems = parent->effective_mems;
> -		cs->use_parent_ecpus = true;
>   	}
>   	spin_unlock_irq(&callback_lock);
>   
> @@ -4194,9 +4175,6 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
>   	    is_sched_load_balance(cs))
>   		update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
>   
> -	if (cs->use_parent_ecpus)
> -		cs->use_parent_ecpus = false;
> -
>   	cpuset_dec();
>   	clear_bit(CS_ONLINE, &cs->flags);
>   

LGTM

Reviewed-by: Waiman Long <longman@...hat.com>