Re: [PATCH 2/2] sched/uclamp: Add uclamp_is_used() check before enable it

[Hongyan Xia]

On 13/02/2025 09:15, Xuewen Yan wrote:
> Because the static_branch_enable() would get the cpus_read_lock(),
> and sometimes users may frequently set the uclamp value of tasks,
> and the uclamp_validate() would call the static_branch_enable()
> frequently, so add the uclamp_is_used() check to prevent calling
> the cpus_read_lock() frequently.
>
> Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
> ---
>   kernel/sched/syscalls.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
> index 456d339be98f..d718fddadb03 100644
> --- a/kernel/sched/syscalls.c
> +++ b/kernel/sched/syscalls.c
> @@ -368,7 +368,8 @@ static int uclamp_validate(struct task_struct *p,
>   	 * blocking operation which obviously cannot be done while holding
>   	 * scheduler locks.
>   	 */
> -	static_branch_enable(&sched_uclamp_used);
> +	if (!uclamp_is_used())
> +		static_branch_enable(&sched_uclamp_used);

NIT: I was also wondering about race conditions, and then realized we 
never disable this static key, so maybe worth adding a comment here.

>   
>   	return 0;
>   }

Reviewed-by: Hongyan Xia <hongyan.xia2@xxxxxxx>