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

[Christian Loehle <christian.loehle@arm.com>]

On 2/13/25 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@unisoc.com>
> ---
>  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);
>  
>  	return 0;
>  }

Given that we never disable sched_uclamp_used once active this
is fine.
Reviewed-by: Christian Loehle <christian.loehle@arm.com>