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

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Message-ID: <CADYu308at=9Dx3oxtDjwKDcax6LorJGi59VYBeAmTmyJCeT2LQ@mail.gmail.com>
Date:	Wed, 9 Dec 2015 00:51:06 +0530
From:	Aniroop Mathur <aniroop.mathur@...il.com>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>, 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
 usleep_range for more than 20ms delay ?

On Tue, Dec 8, 2015 at 2:33 PM, Clemens Ladisch <clemens@...isch.de> wrote:
> Aniroop Mathur wrote:
>> As in the kernel documentation, it is mentioned to use msleep for
>> 10ms+ delay, I am confused whether there would be any disadvantage in
>> using usleep_range for higher delays values because normally drivers
>> have variety of delays used (2, 10, 20, 40, 100, 500 ms).
>>
>> So, could you please help to confirm that if we use usleep_range for
>> inserting delays greater than 20 ms, would it be harmful or beneficial
>> or does not make any difference at all ?
>
> As the documentation told you, usleep_range() is likely to require
> a separate interrupt, while msleep() is likely to round to some other,
> already-scheduled interrupt.  The former is possibly harmful regarding
> CPU and power usage; you have to balance it against your need for
> accuracy.
>

Thank you for the answer!
usleep_range will generate an interrupt to achieve accuracy.
However, would that be considered as harmful or a disadvantage ?
Would the power usage and cpu really substantial ?

PS: I have added my more concern and explanation in another email
thread whose subject misses u in usleep_range, by mistake. Added
you in it as well.

> (And usleep_range() has a 32-bit nanosecond limit on 32-bit
> architectures.)
>
>
> Regards,
> Clemens
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