linux-kernel - Re: [PATCH v12 3/4] cpuidle: Export the next timer/tick expiration for a CPU

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Date:   Thu, 21 Mar 2019 11:04:08 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org
Cc:     Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Mark Rutland <mark.rutland@....com>,
        "Raju P . L . S . S . S . N" <rplsssn@...eaurora.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        Kevin Hilman <khilman@...nel.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 3/4] cpuidle: Export the next timer/tick expiration
 for a CPU

On 27/02/2019 20:58, Ulf Hansson wrote:
> To be able to predict the sleep duration for a CPU that is entering idle,
> knowing when the next timer/tick is going to expire, is extremely useful.
> Both the teo and the menu cpuidle governors already makes use of this
> information, while selecting an idle state.
> 
> Moving forward, the similar prediction needs to be done, but for a group of
> idle CPUs rather than for a single idle CPU. Following changes implements a
> new genpd governor, which needs this.
> 
> Support this, by sharing a new function called
> tick_nohz_get_next_hrtimer(), which returns the next hrtimer or the next
> tick, whatever that expires first.
> 
> Additionally, when cpuidle is about to invoke the ->enter() callback, then
> call tick_nohz_get_next_hrtimer() and store its return value in the per CPU
> struct cpuidle_device, as to make it available outside cpuidle.
> 
> Do note, at the point when cpuidle calls tick_nohz_get_next_hrtimer(), the
> governor's ->select() callback has already made a decision whether to stop
> the tick or not. In this way, tick_nohz_get_next_hrtimer() actually returns
> the next timer expiration, whatever origin.
> 
> Cc: Lina Iyer <ilina@...eaurora.org>
> Co-developed-by: Lina Iyer <lina.iyer@...aro.org>
> Co-developed-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> ---

Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org>

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