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Re: [Ntp] Resending: Thoughts on draft-ietf-ntp-refid-updates

Martin Burnicki <martin.burnicki@meinberg.de> Fri, 20 July 2018 14:00 UTC

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To: Daniel Franke <dfoxfranke@gmail.com>, ntp@ietf.org
Cc: ask@develooper.com
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From: Martin Burnicki <martin.burnicki@meinberg.de>
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Date: Fri, 20 Jul 2018 16:00:24 +0200
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Archived-At: <https://mailarchive.ietf.org/arch/msg/ntp/oaa7dfs4tbuJFODuGCvVU46Otec>
Subject: Re: [Ntp] Resending: Thoughts on draft-ietf-ntp-refid-updates
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Daniel Franke wrote:
> On Fri, Jul 20, 2018 at 9:33 AM Martin Burnicki
> <martin.burnicki@meinberg.de> wrote:
>> Please don't blame ntpd for smearing leap seconds.
>>
>> The leap second is inserted/handled by the kernel, and that's basically
>> the way it should be.
>>
>> However, this is often done in a way that applications may become
>> confused if the system time is simply stepped back by 1 s.
>>
>> If you used any other time synchronization software which just passes a
>> leap second announcement to the kernel then the applications will have
>> the same problems.
>>
>> Leap second smearing by an NTP server is just an optional way to avoid
>> these problems because there's no better way to get around it.
> 
> In a better world, both NTP time and POSIX time would be TAI-based,
> and leap second updates would be handled through the time zone
> facility, with UTC being just another local time zone. Alas, that ship
> sailed away a long time ago.

Unfortunately, yes.

> In a slightly worse world still better than the current one, NTP would
> provide unsmeared time to the kernel, which would provide smeared time
> through the what-ought-to-be-legacy POSIX APIs, and unsmeared time
> through a new better-designed API that expresses time as
> whole-days-since-epoch + seconds-since midnight, so that time can be
> expressed unambiguously during leap seconds. That ship, too, has
> lifted anchor, but maybe it's not too late to jump onto it.

Again, I absolutely agree with you.

However, Steve Summit has proposed a kernel patch which introduces some
new clock IDs for clock_gettime(), which return the time according to
different "clock models", including a time smeared by the kernel.

This sounds like a good solution to me.

Martin
-- 
Martin Burnicki

Senior Software Engineer

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