Re: [PATCH v1] sched: idle: Make skipping governor callbacks more consistent

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

On 3/7/26 16:12, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> If the cpuidle governor .select() callback is skipped because there
> is only one idle state in the cpuidle driver, the .reflect() callback
> should be skipped as well, at least for consistency (if not for
> correctness), so do it.
> 
> Fixes: e5c9ffc6ae1b ("cpuidle: Skip governor when only one idle state is available")
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/cpuidle/cpuidle.c |   10 ----------
>  kernel/sched/idle.c       |   11 ++++++++++-
>  2 files changed, 10 insertions(+), 11 deletions(-)
> 
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -359,16 +359,6 @@ noinstr int cpuidle_enter_state(struct c
>  int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>  		   bool *stop_tick)
>  {
> -	/*
> -	 * If there is only a single idle state (or none), there is nothing
> -	 * meaningful for the governor to choose. Skip the governor and
> -	 * always use state 0 with the tick running.
> -	 */
> -	if (drv->state_count <= 1) {
> -		*stop_tick = false;
> -		return 0;
> -	}
> -
>  	return cpuidle_curr_governor->select(drv, dev, stop_tick);
>  }
>  
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -221,7 +221,7 @@ static void cpuidle_idle_call(void)
>  
>  		next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
>  		call_cpuidle(drv, dev, next_state);
> -	} else {
> +	} else if (drv->state_count > 1) {
>  		bool stop_tick = true;
>  
>  		/*
> @@ -239,6 +239,15 @@ static void cpuidle_idle_call(void)
>  		 * Give the governor an opportunity to reflect on the outcome
>  		 */
>  		cpuidle_reflect(dev, entered_state);
> +	} else {
> +		tick_nohz_idle_retain_tick();
> +
> +		/*
> +		 * If there is only a single idle state (or none), there is
> +		 * nothing meaningful for the governor to choose.  Skip the
> +		 * governor and always use state 0.
> +		 */
> +		call_cpuidle(drv, dev, 0);
>  	}
>  
>  exit_idle:
> 
> 
> 

Duh, good catch.
Reviewed-by: Christian Loehle <christian.loehle@arm.com>