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Re: [Ntp] Antw: [EXT] Re: CLOCK_TAI (was NTPv5: big picture)

Martin Burnicki <martin.burnicki@meinberg.de> Fri, 08 January 2021 15:47 UTC

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To: Warner Losh <imp@bsdimp.com>
Cc: Doug Arnold <doug.arnold@meinberg-usa.com>, Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>, "mlichvar@redhat.com" <mlichvar@redhat.com>, "emmanuel.fuste@thalesgroup.com" <emmanuel.fuste@thalesgroup.com>, "ntp@ietf.org" <ntp@ietf.org>, "magnus@rubidium.se" <magnus@rubidium.se>
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From: Martin Burnicki <martin.burnicki@meinberg.de>
Organization: Meinberg Funkuhren GmbH & Co. KG, Bad Pyrmont, Germany
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Date: Fri, 08 Jan 2021 16:47:15 +0100
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Subject: Re: [Ntp] Antw: [EXT] Re: CLOCK_TAI (was NTPv5: big picture)
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Warner Losh said:
> On Fri, Jan 8, 2021, 8:22 AM Martin Burnicki
> <martin.burnicki=40meinberg.de@dmarc.ietf.org
> <mailto:40meinberg.de@dmarc.ietf.org>> wrote:
> 
>     Doug Arnold wrote:
>     > I think that the point of a leap smear is that no special handling
>     of leap seconds is needed by the client.  It is introduced gradually
>     over a number of polling periods.
> 
>     That's exactly the point. You want to hide the leap second from the
>     client to avoid that *applications* run into problems when the kernel
>     just steps the time back by 1 second.
> 
> 
> My fundamental position on leap seconds hasn't changed in 20 years: they
> are evil and must die. Earth clocks and atomic clocks need a different
> way to synchronize.

Agreed. But as long as there is no decision to abolish them, we have to
live with them, and have the same discussions over and over again. ;-)

> Leap seconds generate dozens of edge cases,
> operational difficulties and data dependencies that complicate time for
> everyone and all that added complication has a cost that far exceeds the
> benefit. 
> 
> Smearing is the latest way to paper over all this and keep applications
> naive. I'm not sure if I view it as a brilliant hack to protect the
> applications from a rushed standard we are stuck with, or a deeply
> worrying "enabling" of bad behavior by applications, libraries and
> operating systems. 

The biggest problem I see with smearing in general is to decide if
applications that require millisecond accuracy can tolerate offsets up
to +/- 0.5 or even 1 s in this special case.

Beside this, there are lots of potential problems due to different
shapes and intervals for the smearing.


Martin
-- 
Martin Burnicki

Senior Software Engineer

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