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 18:29:00 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Shreyas B Prabhu <shreyas@...ux.vnet.ibm.com>
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

On 02/22/2016 04:02 PM, Shreyas B Prabhu wrote:
> 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().

That is a good point but the function is not supposed to be called in 
the rcu_idle_enter/rcu_idle_exit section which is inside 
cpuidle_idle_call().


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