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

Terje Mathisen terje.mathisen at tmsw.no
Mon Jan 26 17:45:58 UTC 2015


Miroslav Lichvar wrote:
> On Mon, Jan 26, 2015 at 01:03:48PM +0100, Terje Mathisen wrote:
>> One of the good points about Google's smear is the fact that they use a half
>> cosine to distribute the offset, which means that they have a time function
>> which is both continuous and monotonic, as well as having an infinite number
>> of defined derivatives, i.e. it is maximally smooth.
>
> They could have chosen a better function though. If its second
> derivative (wander) started at zero, the NTP clients could adjust
> their polling interval if necessary before the error gets large and
> the maximum error between the clients could be minimized.
>
> 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?

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?

Terje

-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"



More information about the questions mailing list