linux-kernel - Re: [RFT] [PATCH v2] cpuidle: menu: Skip tick_nohz_get_sleep

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Date:   Mon, 14 Aug 2023 07:51:41 -0700
From:   Doug Smythies <dsmythies@...us.net>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Kajetan Puchalski <kajetan.puchalski@....com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Doug Smythies <dsmythies@...us.net>
Subject: Re: [RFT] [PATCH v2] cpuidle: menu: Skip tick_nohz_get_sleep_length()
 call in some cases

On Thu, Aug 10, 2023 at 11:38 AM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Subject: [PATCH] cpuidle: menu: Skip tick_nohz_get_sleep_length() call in some cases
>
> Because the cost of calling tick_nohz_get_sleep_length() may increase
> in the future, reorder the code in menu_select() so it first uses the
> statistics to determine the expected idle duration.  If that value is
> higher than RESIDENCY_THRESHOLD_NS, tick_nohz_get_sleep_length() will
> be called to obtain the time till the closest timer and refine the
> idle duration prediction if necessary.
>
> This causes the governor to always take the full overhead of
> get_typical_interval() with the assumption that the cost will be
> amortized by skipping the tick_nohz_get_sleep_length() call in the
> cases when the predicted idle duration is relatively very small.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

I ran the same tests as I did for the teo governor changes.
Nothing of significance to report (well, some minor improvements
in records per second at the long interval end of the sleeping
ebizzy test, with a corresponding slight increase in processor
package power).

Tested-by: Doug Smythies <dsmythies@...us.net>

> ---
>
> v1 -> v2: Add missing max check to get_typical_interval().
>

... Doug