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

Miroslav Lichvar mlichvar at redhat.com
Mon Jan 26 13:27:41 UTC 2015


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

-- 
Miroslav Lichvar


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