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

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Message-ID: <CAJZ5v0ggvvSnV8qvoOhOKBAMkmERzr22rqgqKV--fny1q35M+g@mail.gmail.com>
Date:   Thu, 17 Aug 2023 11:29:15 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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>
Subject: Re: [RFT] [PATCH v2] cpuidle: menu: Skip tick_nohz_get_sleep_length()
 call in some cases

On Mon, Aug 14, 2023 at 4:52 PM Doug Smythies <dsmythies@...us.net> wrote:
>
> 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>

Thank you!