[ntp:questions] NTP roadmap (was Re: Poul-Henning Kamp and re-write of NTP)
stenn at ntp.org
Tue Dec 9 08:23:37 UTC 2014
William Unruh writes:
> On 2014-12-09, skillzero at gmail.com <skillzero at gmail.com> wrote:
>> On Sunday, December 7, 2014 7:25:01 PM UTC-8, Harlan Stenn wrote:
>>> Rob writes:
>>>> It has been discussed before that reference clock drivers should be
>>>> loadable modules or even separate processes.
>>> A complete rewrite of the full NTP software is slated for post-4.2.8.
>>> We're expecting (the names might be changed):
>>> - tsc - Time Sync Client: a leaf-client. PHK is working on this.
>> Are there any plans to incorporate ideas from RADclock? The PLL that
>> PHK mentions on his site implies a feedback model. I'm wondering if
>> any thought has been given to a feed forward design (e.g. determine
>> frequency based on raw ticks). Or was that model considered and
> Why would one want feedforward? You surely want the system to correct
> the errors in the local clock, and those are not constant or
> predictable. Temperature, crystal aging, maybe even computer load and
> voltages will all affect the clock in undetermined and undeterminable
Bill, have you read about RADclock?
> It would seem to me that the key parameter is the reach of the
> feedback-- does one only use the current error to correct the system,
> or does one use a longer stretch of errors to correct the system. The
> latter allow one at least in part to separate the random influences
> from the uniform errors-- the random errors get knocked down by the
> averaging of the fluctuations. Exactly which is best for time control
> still needs more study, but as mentioned, in the comparison of ntpd
> (PLL) and chrony (regression) it seems as if chrony wins in its speed
> of response to outside influences and in its ability to control the
> clock to track UTC.
> But I guess we all have our favourites.
Yes, and your/chrony's definition of "best time" isn't the same as the
one NTP uses.
If you use NTP's model, NTP keeps better time than chrony.
If you use chrony's modle, it keeps better time than NTP.
Harlan Stenn <stenn at ntp.org>
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