* [PATCH] cgroup/cpuset: simplify the percpu kthreads check in update_tasks_cpumask()
@ 2023-07-04 11:30 Miaohe Lin
2023-07-05 3:14 ` Waiman Long
2023-07-10 20:25 ` Tejun Heo
0 siblings, 2 replies; 5+ messages in thread
From: Miaohe Lin @ 2023-07-04 11:30 UTC (permalink / raw)
To: longman, tj, hannes, lizefan.x; +Cc: cgroups, linux-kernel, linmiaohe
kthread_is_per_cpu() can be called directly without checking whether
PF_KTHREAD is set in task->flags. So remove PF_KTHREAD check to make
code more concise.
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
kernel/cgroup/cpuset.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 58e6f18f01c1..601c40da8e03 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1230,7 +1230,7 @@ static void update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
/*
* Percpu kthreads in top_cpuset are ignored
*/
- if ((task->flags & PF_KTHREAD) && kthread_is_per_cpu(task))
+ if (kthread_is_per_cpu(task))
continue;
cpumask_andnot(new_cpus, possible_mask, cs->subparts_cpus);
} else {
--
2.33.0
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] cgroup/cpuset: simplify the percpu kthreads check in update_tasks_cpumask()
2023-07-04 11:30 [PATCH] cgroup/cpuset: simplify the percpu kthreads check in update_tasks_cpumask() Miaohe Lin
@ 2023-07-05 3:14 ` Waiman Long
2023-07-05 5:56 ` Miaohe Lin
2023-07-10 20:25 ` Tejun Heo
1 sibling, 1 reply; 5+ messages in thread
From: Waiman Long @ 2023-07-05 3:14 UTC (permalink / raw)
To: Miaohe Lin, tj, hannes, lizefan.x; +Cc: cgroups, linux-kernel
On 7/4/23 07:30, Miaohe Lin wrote:
> kthread_is_per_cpu() can be called directly without checking whether
> PF_KTHREAD is set in task->flags. So remove PF_KTHREAD check to make
> code more concise.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
> kernel/cgroup/cpuset.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 58e6f18f01c1..601c40da8e03 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1230,7 +1230,7 @@ static void update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
> /*
> * Percpu kthreads in top_cpuset are ignored
> */
> - if ((task->flags & PF_KTHREAD) && kthread_is_per_cpu(task))
> + if (kthread_is_per_cpu(task))
> continue;
> cpumask_andnot(new_cpus, possible_mask, cs->subparts_cpus);
> } else {
The initial intention was to ignore only percpu kthreads. The current
code likely ignore all the kthreads. Removing the PF_KTHREAD flag,
however, may introduce unexpected regression at this point. I would like
to hold off for now until more investigation are done.
Thanks,
Longman
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] cgroup/cpuset: simplify the percpu kthreads check in update_tasks_cpumask()
2023-07-05 3:14 ` Waiman Long
@ 2023-07-05 5:56 ` Miaohe Lin
2023-07-05 14:49 ` Waiman Long
0 siblings, 1 reply; 5+ messages in thread
From: Miaohe Lin @ 2023-07-05 5:56 UTC (permalink / raw)
To: Waiman Long; +Cc: cgroups, linux-kernel, tj, hannes, lizefan.x
On 2023/7/5 11:14, Waiman Long wrote:
> On 7/4/23 07:30, Miaohe Lin wrote:
>> kthread_is_per_cpu() can be called directly without checking whether
>> PF_KTHREAD is set in task->flags. So remove PF_KTHREAD check to make
>> code more concise.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> ---
>> kernel/cgroup/cpuset.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 58e6f18f01c1..601c40da8e03 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -1230,7 +1230,7 @@ static void update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
>> /*
>> * Percpu kthreads in top_cpuset are ignored
>> */
>> - if ((task->flags & PF_KTHREAD) && kthread_is_per_cpu(task))
>> + if (kthread_is_per_cpu(task))
>> continue;
>> cpumask_andnot(new_cpus, possible_mask, cs->subparts_cpus);
>> } else {
>
> The initial intention was to ignore only percpu kthreads. The current code likely ignore all the kthreads. Removing the PF_KTHREAD flag, however, may introduce unexpected regression at this point. I would like to hold off for now until more investigation are done.
IMHO, the current code will ignore only percpu kthreads:
1.If PF_KTHREAD is set in task->flags, this patch doesn't make any difference.
2.If PF_KTHREAD is not set in task->flags, kthread_is_per_cpu will *always return false*. So this patch doesn't make any functional change.
bool kthread_is_per_cpu(struct task_struct *p)
{
struct kthread *kthread = __to_kthread(p);
if (!kthread)
return false;
....
}
static inline struct kthread *__to_kthread(struct task_struct *p)
{
void *kthread = p->worker_private;
if (kthread && !(p->flags & PF_KTHREAD))
^^^^^^^^^^^^^^^^^^^^^^
PF_KTHREAD is not set, so kthread = NULL.
kthread = NULL;
return kthread;
}
Or am I miss something? Thanks for comment and review.
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] cgroup/cpuset: simplify the percpu kthreads check in update_tasks_cpumask()
2023-07-05 5:56 ` Miaohe Lin
@ 2023-07-05 14:49 ` Waiman Long
0 siblings, 0 replies; 5+ messages in thread
From: Waiman Long @ 2023-07-05 14:49 UTC (permalink / raw)
To: Miaohe Lin; +Cc: cgroups, linux-kernel, tj, hannes, lizefan.x
On 7/5/23 01:56, Miaohe Lin wrote:
> On 2023/7/5 11:14, Waiman Long wrote:
>> On 7/4/23 07:30, Miaohe Lin wrote:
>>> kthread_is_per_cpu() can be called directly without checking whether
>>> PF_KTHREAD is set in task->flags. So remove PF_KTHREAD check to make
>>> code more concise.
>>>
>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>> ---
>>> kernel/cgroup/cpuset.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>>> index 58e6f18f01c1..601c40da8e03 100644
>>> --- a/kernel/cgroup/cpuset.c
>>> +++ b/kernel/cgroup/cpuset.c
>>> @@ -1230,7 +1230,7 @@ static void update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
>>> /*
>>> * Percpu kthreads in top_cpuset are ignored
>>> */
>>> - if ((task->flags & PF_KTHREAD) && kthread_is_per_cpu(task))
>>> + if (kthread_is_per_cpu(task))
>>> continue;
>>> cpumask_andnot(new_cpus, possible_mask, cs->subparts_cpus);
>>> } else {
>> The initial intention was to ignore only percpu kthreads. The current code likely ignore all the kthreads. Removing the PF_KTHREAD flag, however, may introduce unexpected regression at this point. I would like to hold off for now until more investigation are done.
> IMHO, the current code will ignore only percpu kthreads:
> 1.If PF_KTHREAD is set in task->flags, this patch doesn't make any difference.
> 2.If PF_KTHREAD is not set in task->flags, kthread_is_per_cpu will *always return false*. So this patch doesn't make any functional change.
>
> bool kthread_is_per_cpu(struct task_struct *p)
> {
> struct kthread *kthread = __to_kthread(p);
> if (!kthread)
> return false;
> ....
> }
>
> static inline struct kthread *__to_kthread(struct task_struct *p)
> {
> void *kthread = p->worker_private;
> if (kthread && !(p->flags & PF_KTHREAD))
> ^^^^^^^^^^^^^^^^^^^^^^
> PF_KTHREAD is not set, so kthread = NULL.
> kthread = NULL;
> return kthread;
> }
>
> Or am I miss something? Thanks for comment and review.
Yes, you are right. I was that conscious when I reviewed the patch last
night :-)
Reviewed-by: Waiman Long <longman@redhat.com>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] cgroup/cpuset: simplify the percpu kthreads check in update_tasks_cpumask()
2023-07-04 11:30 [PATCH] cgroup/cpuset: simplify the percpu kthreads check in update_tasks_cpumask() Miaohe Lin
2023-07-05 3:14 ` Waiman Long
@ 2023-07-10 20:25 ` Tejun Heo
1 sibling, 0 replies; 5+ messages in thread
From: Tejun Heo @ 2023-07-10 20:25 UTC (permalink / raw)
To: Miaohe Lin; +Cc: longman, hannes, lizefan.x, cgroups, linux-kernel
On Tue, Jul 04, 2023 at 07:30:49PM +0800, Miaohe Lin wrote:
> kthread_is_per_cpu() can be called directly without checking whether
> PF_KTHREAD is set in task->flags. So remove PF_KTHREAD check to make
> code more concise.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Applied to cgroup/for-6.6.
Thanks.
--
tejun
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2023-07-10 20:25 UTC | newest]
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2023-07-04 11:30 [PATCH] cgroup/cpuset: simplify the percpu kthreads check in update_tasks_cpumask() Miaohe Lin
2023-07-05 3:14 ` Waiman Long
2023-07-05 5:56 ` Miaohe Lin
2023-07-05 14:49 ` Waiman Long
2023-07-10 20:25 ` Tejun Heo
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