linux-kernel - Re: [PATCH v1 4/9] cpuidle: teo: Drop local variable prev_intercept

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Message-ID: <d4bcd083-11fd-48b6-9dab-30717f3080d4@arm.com>
Date: Wed, 15 Jan 2025 19:46:14 +0000
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>,
 Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Subject: Re: [PATCH v1 4/9] cpuidle: teo: Drop local variable
 prev_intercept_idx

On 1/13/25 18:40, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Local variable prev_intercept_idx in teo_select() is redundant becase

s/becase/because

> it cannot be 0 when candidate state index is 0.
> 
> The prev_intercept_idx value is the index of the deepest enabled idle
> state, so if it is 0, state 0 is the deepest enabled idle state, in
> which case it must be the only enabled idle state, but then teo_select()
> would have returned early before initializing prev_intercept_idx.
> 
> Thus prev_intercept_idx must be nonzero and the check of it against 0
> always passes, so it can be dropped altogether.
> 
> No intentional functional impact.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpuidle/governors/teo.c |   15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -292,7 +292,6 @@
>  	unsigned int hit_sum = 0;
>  	int constraint_idx = 0;
>  	int idx0 = 0, idx = -1;
> -	int prev_intercept_idx;
>  	s64 duration_ns;
>  	int i;
>  
> @@ -370,7 +369,6 @@
>  	 * all of the deeper states, a shallower idle state is likely to be a
>  	 * better choice.
>  	 */
> -	prev_intercept_idx = idx;
>  	if (2 * idx_intercept_sum > cpu_data->total - idx_hit_sum) {
>  		int first_suitable_idx = idx;
>  
> @@ -437,14 +435,11 @@
>  		idx = constraint_idx;
>  
>  	if (!idx) {
> -		if (prev_intercept_idx) {
> -			/*
> -			 * Query the sleep length to be able to count the wakeup
> -			 * as a hit if it is caused by a timer.
> -			 */
> -			duration_ns = tick_nohz_get_sleep_length(&delta_tick);
> -			cpu_data->sleep_length_ns = duration_ns;
> -		}
> +		/*
> +		 * Query the sleep length to be able to count the wakeup as a
> +		 * hit if it is caused by a timer.
> +		 */
> +		cpu_data->sleep_length_ns = tick_nohz_get_sleep_length(&delta_tick);
>  		goto out_tick;

Just like the previous one:
Reviewed-by: Christian Loehle <christian.loehle@....com>