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

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Date:	Thu, 18 Feb 2016 00:09:14 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH V3 2/2] sched: idle: IRQ based next prediction for idle period

On Tue, Feb 16, 2016 at 5:44 PM, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> On Tue, 16 Feb 2016, Daniel Lezcano wrote:
>
>> Many IRQs are quiet most of the time, or they tend to come in bursts of
>> fairly equal time intervals within each burst. It is therefore possible
>> to detect those IRQs with stable intervals and guestimate when the next
>> IRQ event is most likely to happen.
>>
>> Examples of such IRQs may include audio related IRQs where the FIFO size
>> and/or DMA descriptor size with the sample rate create stable intervals,
>> block devices during large data transfers, etc.  Even network streaming
>> of multimedia content creates patterns of periodic network interface IRQs
>> in some cases.
>>
>> This patch adds code to compute the mean interval and variance for each IRQ
>> over a window of time intervals between IRQ events. Those statistics can
>> be used to assist cpuidle in selecting the most appropriate sleep state
>> by predicting the most likely time for the next interrupt.
>>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
>
> The math in next_irq_event() is correct even though I think it could be
> done more simply.  But that can be optimized at a later time.
>
> Reviewed-by: Nicolas Pitre <nico@...aro.org>

Well, I'm likely overlooking something, but how is this going to be
hooked up to the code in idle.c?

Thanks,
Rafael