linux-kernel - Re: [RFC/RFT][PATCH 6/7] sched: idle: Predict idle duration before stopping the tick

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Message-ID: <2173697.qZXBTo6fPi@aspire.rjw.lan>
Date:   Tue, 06 Mar 2018 09:18:04 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Rik van Riel <riel@...riel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Thomas Ilsche <thomas.ilsche@...dresden.de>,
        Doug Smythies <dsmythies@...us.net>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Mike Galbraith <mgalbraith@...e.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [RFC/RFT][PATCH 6/7] sched: idle: Predict idle duration before stopping the tick

On Tuesday, March 6, 2018 12:27:01 AM CET Rik van Riel wrote:
> On Sun, 2018-03-04 at 23:28 +0100, Rafael J. Wysocki wrote:
> > 
> > +++ linux-pm/kernel/sched/idle.c
> > @@ -188,13 +188,14 @@ static void cpuidle_idle_call(void)
> >  	} else {
> >  		unsigned int duration_us;
> >  
> > -		tick_nohz_idle_go_idle(true);
> > -		rcu_idle_enter();
> > -
> >  		/*
> >  		 * Ask the cpuidle framework to choose a convenient
> > idle state.
> >  		 */
> >  		next_state = cpuidle_select(drv, dev, &duration_us);
> > +
> > +		tick_nohz_idle_go_idle(duration_us > USEC_PER_SEC /
> > HZ);
> > +		rcu_idle_enter();
> > +
> >  		entered_state = call_cpuidle(drv, dev, next_state);
> 
> When the expected idle period is short enough
> that the timer is not stopped, does it make
> sense to still call rcu_idle_enter?
> 
> Should rcu_idle_enter also be conditional on
> the expected idle period?

Well, that would be the next step. :-)