[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


Richard,

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.

Dave

Richard B. Gilbert wrote:

> <snip>
> 
> 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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