linux-kernel - Re: Ques: [kernel/time/*] Is there any disadvantage in using sleep

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Message-ID: <alpine.DEB.2.11.1512081147050.3595@nanos>
Date:	Tue, 8 Dec 2015 11:48:39 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Aniroop Mathur <aniroop.mathur@...il.com>
cc:	John Stultz <john.stultz@...aro.org>, a.mathur@...sung.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Ques: [kernel/time/*] Is there any disadvantage in using
 sleep_range for more than 20ms delay ?

On Tue, 8 Dec 2015, Aniroop Mathur wrote:
> On Tue, Dec 8, 2015 at 12:07 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > The real question is how precise must your delay be? If the delay
> > needs to be precise within the min/max sleep time limits, then
> > usleep_range() is probably the way to go. If the delay can be
> > imprecise then using msleep() is the right way because that lets the
> > kernel batch timers for power saving purposes.
>
> Thank you for the answer !
> Normally, we insert delays in driver while enabling the chip.
> So here usleep_range seems to service better as we do not want to delay
> the initialisation process of chip and make it ready to generate data,
> especially for faster devices like sensor.

The initialization process is hardly something critical, so why would
the delay need to be precise? What's the point of having data 10ms
earlier?
 
> One last thing,
> Considering HZ=100, would the power saving be same if we set the
> range in usleep_range equivalent to msleep ?
> For example: msleep (33) and usleep_range(33000, 40000)
> So for such case, would both have same impact on power saving ?

Probably, but what's the point of doing that?

Thanks,

	tglx
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