[ntp:questions] NTP offset doesn't change.

William Unruh unruh at invalid.ca
Wed Feb 11 17:17:31 UTC 2015


On 2015-02-11, Harlan Stenn <stenn at ntp.org> wrote:
> William Unruh writes:
>> On 2015-02-11, Harlan Stenn <stenn at ntp.org> wrote:
>> > It's one thing if a system rarely steps.  It's a bit different if those
>> > steps happen more frequently.
>> 
>> Yes. And it is either equally rare that the system will go over 500PPM,
>> but sometimes a computer can have a large "natural" drift, (even over
>> 500PPM) and that will drastically reduce the "headroom" to deal with
>> unusual situations. (ie, if the computers normal drift is 400PPM, that
>> means that the effective cap is only 100PPM, not 500). 
>> stepping is much worse than high PPM since it is infinite PPM. 
>
> Where would you get the idea that a 400ppm swing would be "normal"?
> Or even 200PPM?

I did NOT say a 400PPM swing. I said a static 400PPM drift. That would
then only allow a 100PPM headroom for dynamic drifts. Or if one had a
498PPM static drift, one would be left with a 2PPM headroom. 

>
>> Note that were ntpd designed for 5000 PPM then anything else could
>> follow it since it could also do 5000 PPM. 
>
> Sure, and if it was designed for 10S/S it would handle 10S/S swings.  But
> none of this has been shown to be normal or useful.

Most drifts are static drifts, not swings. ntpd does not differentiate.

>
>> Yes, we are talking about choices. And all I was saying was that this
>> particular choice was somewhat arbitrary. 
>
> That depends on your definition of "somewhat".
>
> More or less, "everything tastes like chicken".  More or less...
>
> H



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