[ntp:questions] NTP vs chrony comparison (Was: oscillations in ntp clock synchronization)
David L. Mills
mills at udel.edu
Fri Jan 25 05:57:08 UTC 2008
The default minpoll of 64 s was chosen on the basis of expected use not
only on fast Ethernets but on paths elsewhere in the Internet where a
smaller time constant can result in a good deal of flap. Setting minpoll
to 16 s results in a zero crossing of a little over ten minutes while
still preserving the shape of the impulse response. In principle, the
time constant could be even smaller, but I wouldn't want to do that
ouside a fast LAN.
Richard B. Gilbert wrote:
> You are certainly at liberty to write your own version that does it your
> way. The startup performance of ntpd seems a little clumsy to me and I
> think that I could do it better by hand if I had knobs to tweak. OTOH I
> see it in ONE setting on ONE network and ntpd really has to work on the
> streets of New York, Vancouver, and "Podunk".
> I use a GPS timing receiver as a reference clock and what I see when
> ntpd starts up is that it makes a "mad dash" for zero offset, overshoots
> and then "rings" for a while. It gets where it's going eventually and I
> normally run the machine 24x7 except during power outrages that last
> longer than my UPS battery so it's not a big issue for me.
> If I had the knobs to control it I would "tap the brakes" gently as it
> approached zero offset with the objective of reaching zero offset and
> the correct frequency simultaneously. But I don't have the math I'd
> need to tamper with the code intelligently nor do I have the experience
> to make it work under all the conditions likely to be encountered.
> Dave and his crew DO have that knowledge and experience and I'm glad
> that they are willing to share it with us.
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