[PATCH -next] cgroup/cpuset: remove child_ecpus_count

[PATCH -next] cgroup/cpuset: remove child_ecpus_count

[Chen Ridong]

The child_ecpus_count variable was previously used to update
sibling cpumask when parent's effective_cpus is updated. However, it became
obsolete after commit e2ffe502ba45 ("cgroup/cpuset: Add
cpuset.cpus.exclusive for v2"). It should be removed.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
---
 kernel/cgroup/cpuset.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 40ec4abaf440..146bf9258db2 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -188,10 +188,8 @@ struct cpuset {
 	/*
 	 * Default hierarchy only:
 	 * use_parent_ecpus - set if using parent's effective_cpus
-	 * child_ecpus_count - # of children with use_parent_ecpus set
 	 */
 	int use_parent_ecpus;
-	int child_ecpus_count;
 
 	/*
 	 * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
@@ -1512,7 +1510,6 @@ static void reset_partition_data(struct cpuset *cs)
 	if (!cpumask_and(cs->effective_cpus,
 			 parent->effective_cpus, cs->cpus_allowed)) {
 		cs->use_parent_ecpus = true;
-		parent->child_ecpus_count++;
 		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
 	}
 }
@@ -1689,10 +1686,7 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
 	isolcpus_updated = partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
 	list_add(&cs->remote_sibling, &remote_children);
 	if (cs->use_parent_ecpus) {
-		struct cpuset *parent = parent_cs(cs);
-
 		cs->use_parent_ecpus = false;
-		parent->child_ecpus_count--;
 	}
 	spin_unlock_irq(&callback_lock);
 	update_unbound_workqueue_cpumask(isolcpus_updated);
@@ -2320,12 +2314,9 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 			cpumask_copy(tmp->new_cpus, parent->effective_cpus);
 			if (!cp->use_parent_ecpus) {
 				cp->use_parent_ecpus = true;
-				parent->child_ecpus_count++;
 			}
 		} else if (cp->use_parent_ecpus) {
 			cp->use_parent_ecpus = false;
-			WARN_ON_ONCE(!parent->child_ecpus_count);
-			parent->child_ecpus_count--;
 		}
 
 		if (remote)
@@ -4139,7 +4130,6 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
 		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
 		cs->effective_mems = parent->effective_mems;
 		cs->use_parent_ecpus = true;
-		parent->child_ecpus_count++;
 	}
 	spin_unlock_irq(&callback_lock);
 
@@ -4206,10 +4196,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
 		update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
 
 	if (cs->use_parent_ecpus) {
-		struct cpuset *parent = parent_cs(cs);
-
 		cs->use_parent_ecpus = false;
-		parent->child_ecpus_count--;
 	}
 
 	cpuset_dec();
-- 
2.34.1

Re: [PATCH -next] cgroup/cpuset: remove child_ecpus_count

[Waiman Long]

On 7/23/24 21:08, Chen Ridong wrote:
> The child_ecpus_count variable was previously used to update
> sibling cpumask when parent's effective_cpus is updated. However, it became
> obsolete after commit e2ffe502ba45 ("cgroup/cpuset: Add
> cpuset.cpus.exclusive for v2"). It should be removed.
Thanks for finding that.
>
> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> ---
>   kernel/cgroup/cpuset.c | 13 -------------
>   1 file changed, 13 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 40ec4abaf440..146bf9258db2 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -188,10 +188,8 @@ struct cpuset {
>   	/*
>   	 * Default hierarchy only:
>   	 * use_parent_ecpus - set if using parent's effective_cpus
> -	 * child_ecpus_count - # of children with use_parent_ecpus set
>   	 */
>   	int use_parent_ecpus;
> -	int child_ecpus_count;
>   
>   	/*
>   	 * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
> @@ -1512,7 +1510,6 @@ static void reset_partition_data(struct cpuset *cs)
>   	if (!cpumask_and(cs->effective_cpus,
>   			 parent->effective_cpus, cs->cpus_allowed)) {
>   		cs->use_parent_ecpus = true;
> -		parent->child_ecpus_count++;
>   		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
>   	}
>   }
> @@ -1689,10 +1686,7 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
>   	isolcpus_updated = partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
>   	list_add(&cs->remote_sibling, &remote_children);
>   	if (cs->use_parent_ecpus) {
> -		struct cpuset *parent = parent_cs(cs);
> -
>   		cs->use_parent_ecpus = false;
> -		parent->child_ecpus_count--;
>   	}
You can also remove { } or just set use_parent_ecpus to false.
>   	spin_unlock_irq(&callback_lock);
>   	update_unbound_workqueue_cpumask(isolcpus_updated);
> @@ -2320,12 +2314,9 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
>   			cpumask_copy(tmp->new_cpus, parent->effective_cpus);
>   			if (!cp->use_parent_ecpus) {
>   				cp->use_parent_ecpus = true;
> -				parent->child_ecpus_count++;
>   			}
Just set it to true.
>   		} else if (cp->use_parent_ecpus) {
>   			cp->use_parent_ecpus = false;
> -			WARN_ON_ONCE(!parent->child_ecpus_count);
> -			parent->child_ecpus_count--;
>   		}
Remove {} or set it to false.
>   
>   		if (remote)
> @@ -4139,7 +4130,6 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
>   		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
>   		cs->effective_mems = parent->effective_mems;
>   		cs->use_parent_ecpus = true;
> -		parent->child_ecpus_count++;
>   	}
>   	spin_unlock_irq(&callback_lock);
>   
> @@ -4206,10 +4196,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
>   		update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
>   
>   	if (cs->use_parent_ecpus) {
> -		struct cpuset *parent = parent_cs(cs);
> -
>   		cs->use_parent_ecpus = false;
> -		parent->child_ecpus_count--;
>   	}
>   
Just set it to false.

Cheers,
Longman

Re: [PATCH -next] cgroup/cpuset: remove child_ecpus_count

[chenridong]

On 2024/7/24 10:16, Waiman Long wrote:
> On 7/23/24 21:08, Chen Ridong wrote:
>> The child_ecpus_count variable was previously used to update
>> sibling cpumask when parent's effective_cpus is updated. However, it 
>> became
>> obsolete after commit e2ffe502ba45 ("cgroup/cpuset: Add
>> cpuset.cpus.exclusive for v2"). It should be removed.
> Thanks for finding that.
>>
>> Signed-off-by: Chen Ridong <chenridong@huawei.com>
>> ---
>>   kernel/cgroup/cpuset.c | 13 -------------
>>   1 file changed, 13 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 40ec4abaf440..146bf9258db2 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -188,10 +188,8 @@ struct cpuset {
>>       /*
>>        * Default hierarchy only:
>>        * use_parent_ecpus - set if using parent's effective_cpus
>> -     * child_ecpus_count - # of children with use_parent_ecpus set
>>        */
>>       int use_parent_ecpus;
>> -    int child_ecpus_count;
>>       /*
>>        * number of SCHED_DEADLINE tasks attached to this cpuset, so 
>> that we
>> @@ -1512,7 +1510,6 @@ static void reset_partition_data(struct cpuset *cs)
>>       if (!cpumask_and(cs->effective_cpus,
>>                parent->effective_cpus, cs->cpus_allowed)) {
>>           cs->use_parent_ecpus = true;
>> -        parent->child_ecpus_count++;
>>           cpumask_copy(cs->effective_cpus, parent->effective_cpus);
>>       }
>>   }
>> @@ -1689,10 +1686,7 @@ static int remote_partition_enable(struct 
>> cpuset *cs, int new_prs,
>>       isolcpus_updated = partition_xcpus_add(new_prs, NULL, 
>> tmp->new_cpus);
>>       list_add(&cs->remote_sibling, &remote_children);
>>       if (cs->use_parent_ecpus) {
>> -        struct cpuset *parent = parent_cs(cs);
>> -
>>           cs->use_parent_ecpus = false;
>> -        parent->child_ecpus_count--;
>>       }
> You can also remove { } or just set use_parent_ecpus to false.
>>       spin_unlock_irq(&callback_lock);
>>       update_unbound_workqueue_cpumask(isolcpus_updated);
>> @@ -2320,12 +2314,9 @@ static void update_cpumasks_hier(struct cpuset 
>> *cs, struct tmpmasks *tmp,
>>               cpumask_copy(tmp->new_cpus, parent->effective_cpus);
>>               if (!cp->use_parent_ecpus) {
>>                   cp->use_parent_ecpus = true;
>> -                parent->child_ecpus_count++;
>>               }
> Just set it to true.
>>           } else if (cp->use_parent_ecpus) {
>>               cp->use_parent_ecpus = false;
>> -            WARN_ON_ONCE(!parent->child_ecpus_count);
>> -            parent->child_ecpus_count--;
>>           }
> Remove {} or set it to false.
>>           if (remote)
>> @@ -4139,7 +4130,6 @@ static int cpuset_css_online(struct 
>> cgroup_subsys_state *css)
>>           cpumask_copy(cs->effective_cpus, parent->effective_cpus);
>>           cs->effective_mems = parent->effective_mems;
>>           cs->use_parent_ecpus = true;
>> -        parent->child_ecpus_count++;
>>       }
>>       spin_unlock_irq(&callback_lock);
>> @@ -4206,10 +4196,7 @@ static void cpuset_css_offline(struct 
>> cgroup_subsys_state *css)
>>           update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
>>       if (cs->use_parent_ecpus) {
>> -        struct cpuset *parent = parent_cs(cs);
>> -
>>           cs->use_parent_ecpus = false;
>> -        parent->child_ecpus_count--;
>>       }
> Just set it to false.
> 
> Cheers,
> Longman
> 
> 
> 

Thank you, Longman, I will do that.

I am considering the necessity of use_parent_ecpus. Currently, the 
use_parent_ecpus variable is only utilized within the 
update_sibling_cpumasks function. This implies that if a cpuset is not 
configured to use its parent's effective_cpus, it might not need to 
invoke update_cpumasks_hier. However, the invocation of 
update_cpumasks_hier may not be necessary for a cpuset, regardless of 
whether it uses its parent's effective_cpus, if there is no change in 
the cpuset's effective_cpus.

Is use_parent_ecpus still relevant?
Or, do I miss something?

Thanks
Ridong