linux-kernel - Re: [PATCH V3 2/2] sched: idle: IRQ based next prediction for idle period

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Date:	Mon, 22 Feb 2016 20:32:13 +0530
From:	Shreyas B Prabhu <shreyas@...ux.vnet.ibm.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	tglx@...utronix.de, peterz@...radead.org, rafael@...nel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	nicolas.pitre@...aro.org, vincent.guittot@...aro.org
Subject: Re: [PATCH V3 2/2] sched: idle: IRQ based next prediction for idle
 period

Hi Daniel,

On 02/16/2016 09:13 PM, Daniel Lezcano wrote:
> +
> +/**
> + * sched_idle_next_wakeup - Predict the next wakeup on the current cpu
> + *
> + * The next event on the cpu is based on a statistic approach of the
> + * interrupt events and the timer deterministic value. From the timer
> + * or the irqs, we return the one expected to occur first.
> + *
> + * Returns the expected remaining idle time before being woken up by
> + * an interruption.
> + */
> +s64 sched_idle_next_wakeup(void)
> +{
> +	s64 next_timer = ktime_to_us(tick_nohz_get_sleep_length());
> +	s64 next_irq = next_irq_event();

Since next_irq_event() uses RCU and we are in idle this should probably
be wrapped in RCU_NONIDLE().

> +
> +	return min(next_irq, next_timer);
> +}
> +

Thanks,
Shreyas