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

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Date:   Mon, 05 Mar 2018 18:27:01 -0500
From:   Rik van Riel <riel@...riel.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <fweisbec@...il.com>
Cc:     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 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?

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