linux-kernel - Re: [RFT][PATCH v2 2/3] cpuidle: teo: Skip tick_nohz_get_sleep

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Message-ID: <28e2d9ce-89db-807a-9d39-f2fcccfb2ad4@linutronix.de>
Date:   Fri, 11 Aug 2023 10:52:03 +0200 (CEST)
From:   Anna-Maria Behnsen <anna-maria@...utronix.de>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
cc:     Linux PM <linux-pm@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Kajetan Puchalski <kajetan.puchalski@....com>
Subject: Re: [RFT][PATCH v2 2/3] cpuidle: teo: Skip tick_nohz_get_sleep_length()
 call in some cases

Hi Rafael,

On Thu, 3 Aug 2023, Rafael J. Wysocki wrote:

> Index: linux-pm/drivers/cpuidle/governors/teo.c
> ===================================================================
> --- linux-pm.orig/drivers/cpuidle/governors/teo.c
> +++ linux-pm/drivers/cpuidle/governors/teo.c
> @@ -166,6 +166,12 @@
>   */
>  #define NR_RECENT	9
>  
> +/*
> + * Idle state target residency threshold used for deciding whether or not to
> + * check the time till the closest expected timer event.
> + */
> +#define RESIDENCY_THRESHOLD_NS	(15 * NSEC_PER_USEC)
> +

I would like to understand why this residency threshold is a fixed value
and not related to TICK_NSEC. I'm sure there is a reason for it - but for
me it is not obvious. Can you please explain it to me?

Thanks,

	Anna-Maria