linux-kernel - Re: [PATCH v1 2/5] cpuidle: governors: teo: Avoid fake intercepts produced by tick

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Message-ID: <f32d40ff-dc1d-4c37-a607-77dd9423ec91@arm.com>
Date: Wed, 21 Jan 2026 13:34:46 +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 2/5] cpuidle: governors: teo: Avoid fake intercepts
 produced by tick

On 1/14/26 19:44, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Tick wakeups can lead to fake intercepts that may skew idle state
> selection towards shallow states, so it is better to avoid counting
> them as intercepts.
> 
> For this purpose, add a check causing teo_update() to only count
> tick wakeups as intercepts if intercepts within the tick period
> range are at least twice as frequent as any other events.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpuidle/governors/teo.c |   11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -239,6 +239,17 @@ static void teo_update(struct cpuidle_dr
>  			cpu_data->state_bins[drv->state_count-1].hits += PULSE;
>  			return;
>  		}
> +		/*
> +		 * If intercepts within the tick period range are not frequent
> +		 * enough, count this wakeup as a hit, since it is likely that
> +		 * the tick has woken up the CPU because an expected intercept
> +		 * was not there.  Otherwise, one of the intercepts may have
> +		 * been incidentally preceded by the tick wakeup.
> +		 */
> +		if (3 * cpu_data->tick_intercepts < 2 * total) {
> +			cpu_data->state_bins[idx_timer].hits += PULSE;
> +			return;
> +		}
>  	}

Reviewed-by: Christian Loehle <christian.loehle@....com>
Makes sense to me, let me try to find something that triggers this (often)