[ntp:questions] Leap second to be introduced in June

Miroslav Lichvar mlichvar at redhat.com
Tue Jan 27 08:38:30 UTC 2015

On Mon, Jan 26, 2015 at 06:45:58PM +0100, Terje Mathisen wrote:
> Miroslav Lichvar wrote:
> >Here is a test showing error between two clients of a server
> >smearing.a large offset. With the cosine function you can see a large
> >spike when smearing started.
> >
> >https://mlichvar.fedorapeople.org/tmp/smear_cos.png
> >https://mlichvar.fedorapeople.org/tmp/smear_sinx.png
> >
> This seems wrong!?!
> First of all, you seem to extend the smearing over a million seconds or so?
> I.e. 10-15 days?


> How large is the adjustment to be smeared out?

10000 seconds. It was a test to see how useful is smearing when
bringing an isolated network back to UTC in a controlled manner.

> The google cosine approach starts with a derivate of zero and ends the same
> way, I really can't see how that leads to that huge (more than 128 ms!)
> spike at the start?

The frequency is changing too quickly at start (2nd derivative is at
the maximum) and the clients don't have a chance to shorten their polling
interval to better track the server.

The point is that there are better functions than cosine for this.

Miroslav Lichvar

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