Subject: Re: Ques: [kernel/time/*] Is there any disadvantage in using
 usleep_range for more than 20ms delay ?
To: Aniroop Mathur <aniroop.mathur@gmail.com>
References: <CADYu308GqGO8C2UA1H39u0ASBmRYcaOJD2pGEK2NenqtED_WhA@mail.gmail.com>
Cc: John Stultz <john.stultz@linaro.org>, Thomas Gleixner <tglx@linutronix.de>,
        a.mathur@samsung.com,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
From: Clemens Ladisch <clemens@ladisch.de>
Message-ID: <56669CFF.8040806@ladisch.de>
Date: Tue, 8 Dec 2015 10:03:59 +0100
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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.

(And usleep_range() has a 32-bit nanosecond limit on 32-bit
architectures.)


Regards,
Clemens
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