linux-kernel - Re: [PATCH v1 1/5] cpuidle: governors: teo: Avoid selecting states with zero-size bins

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Message-ID: <0d066ce0-b0bf-43f2-a1c4-56e5ac47cce1@arm.com>
Date: Wed, 21 Jan 2026 13:09:56 +0000
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
 Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Doug Smythies <dsmythies@...us.net>
Subject: Re: [PATCH v1 1/5] cpuidle: governors: teo: Avoid selecting states
 with zero-size bins

On 1/14/26 19:44, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> If the last two enabled idle states have the same target residency which
> is at least equal to TICK_NSET, teo may select the next-to-last one even

s/TICK_NSET/TICK_NSEC

> though the size of that state's bin is 0, which is confusing.
> 
> Prevent that from happening by adding a target residency check to the
> relevant code path.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpuidle/governors/teo.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -388,6 +388,15 @@ static int teo_select(struct cpuidle_dri
>  			while (min_idx < idx &&
>  			       drv->states[min_idx].target_residency_ns < TICK_NSEC)
>  				min_idx++;
> +
> +			/*
> +			 * Avoid selecting a state with a lower index, but with
> +			 * the same target residency as the current candidate
> +			 * one.
> +			 */
> +			if (drv->states[min_idx].target_residency_ns ==
> +					drv->states[idx].target_residency_ns)

We need to check that min_idx isn't disabled though, otherwise we now skip a
potential (enabled) idx==1 if min_idx==2 and min_idx is disabled. 
Other than that LGTM and with that check and the nit above:

Reviewed-by: Christian Loehle <christian.loehle@....com>

> +				goto constraint;
>  		}
>  
>  		/*
> @@ -410,6 +419,7 @@ static int teo_select(struct cpuidle_dri
>  		}
>  	}
>  
> +constraint:
>  	/*
>  	 * If there is a latency constraint, it may be necessary to select an
>  	 * idle state shallower than the current candidate one.
> 
> 
>