linux-kernel - Re: firewire: CLOCK_MONOTONIC

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Message-ID: <53C6633D.9080905@ladisch.de>
Date:	Wed, 16 Jul 2014 13:34:21 +0200
From:	Clemens Ladisch <clemens@...isch.de>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Stefan Richter <stefanr@...6.in-berlin.de>
CC:	linux-kernel@...r.kernel.org,
	linux1394-devel@...ts.sourceforge.net,
	Peter Zijlstra <peterz@...radead.org>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: firewire: CLOCK_MONOTONIC_RAW exposure

Thomas Gleixner wrote:
> I wonder why firewire exposed CLOCK_MONOTONIC_RAW to user space.
>
> What's the purpose of that? CLOCK_MONOTONIC_RAW is the raw time based
> on the initial frequency setup of the clocksource. That can be quite
> off from the NTP corrected frequency which is exposed by
> CLOCK_MONOTONIC.

The purpose is to get a stable clock, i.e., to avoid clock rate changes
caused by NTP corrections.

ALSA is adding CLOCK_MONOTONIC_RAW for the same reason.


Regards,
Clemens
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