[ntp:questions] frequency adjusting only

Unruh unruh-spam at physics.ubc.ca
Wed Apr 30 17:10:57 UTC 2008


m.louvel at gmail.com (maxime louvel) writes:

>On Tue, Apr 29, 2008 at 6:27 PM, Unruh <unruh-spam at physics.ubc.ca> wrote:


>You're right on this point, what I  actually  get with PTP is delay of 100
>usec, with a variation of 10 usec.
>But I'm only interested in the variation as the 100usec can be removed
>easily because it's constant

The delay is probably what ntp also calls the delay-- the time between when
the packet is sent and when it is received back (minus the time spent in
the server) (t4-t1)-(t3-t2) in ntp jargon. 
This is assumed to be symmetric and is already cancelled. The ONLY way to
really measure if there assymetry is to put a real clock on each of the
machines (Ie, a clock synchronized to usec accuracy to UTC-- eg a GPS PPS )
and measure the offset of each of the machines from GPS time.



>>
>>
>> >I might try the other solutions, if yeI do I'll send an email to complete
>> >the results.
>>
>> As I said, I am completely at a loss to know why you would only be getting
>> 1ms using ntp to synchronize. That is much worse than my experience. (Look
>> at flory on www.theory.physics.ubc.ca/chrony/chrony.html which uses ntp vs
>> the other machine which all use chrony. flory's fluctutations are
>> certainly  not 1ms.)
>>

>I have to say that I 'm also surprise of the bad performance of NTP, I will
>try chrony if it is suitable to my nodes (embedded cards, with the latest
>linux kernel).

If it is a 64 bit machine, there is a little bug being tracked down right
now. The latest version of chrony  is 1.23

As I said I get nothing like your inaccuracy with ntp.





More information about the questions mailing list