[ntp:questions] Keeping NTP Honest Redux

David Mills mills at udel.edu
Sat Nov 7 15:27:26 UTC 2009


Richard,

It's amazing how much bullshit is spread by others without checking the 
documentation, the code, the loopstats data and for that matter the 
papers and the book. You correctly observe the poll interval does change 
in response to measured system jitter and oscillator wander. As 
confirmed by experience and the data, the dynamics are quick to respond 
to increasing wander and slow to respond to decreasing wander.

Dave

Richard B. Gilbert wrote:

>Unruh wrote:
>  
>
>>"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:
>>
>>    
>>
>>>Terje Mathisen wrote:
>>>      
>>>
>>>>Evandro Menezes wrote:
>>>>        
>>>>
>>>>>I've come to the conclusion that since NTP doesn't correct for
>>>>>temperature variations, it's long-term compensation is counter-
>>>>>productive.  Therefore, instead of letting the poll period increase to
>>>>>the default 1024s, perhaps it'd be best to limit it to 64s.  However,
>>>>>this requires that each server has the option maxpoll attached to it.
>>>>>It'd be more convenient to have set this parameter for all servers
>>>>>from a single place, such as the old tinker maxpoll option.
>>>>>
>>>>>So, why was tinker maxpoll removed?  Any chance to get it back in?
>>>>>          
>>>>>
>>>>Maybe because the algorithms have been optimized to get the best 
>>>>possible time with minimum load on the servers?
>>>>
>>>>Making it more convenient to lock polling at 64s isn't a good idea, imho.
>>>>        
>>>>
>>>Locking the polling interval at ANY value probably isn't a good idea. 
>>>If not tampered with, NTPD will adjust the polling interval to the 
>>>optimum value for the conditions then obtaining.  The conditions do change.
>>>      
>>>
>>Well, not really. ntp is designed to quite rapidly go to maxpoll of 10
>>and to stay there. The routine is very loath to decrease the poll and
>>quick to increase it, so that it rarely decreases the poll interval. Ie,
>>    
>>
>
>My observations do not support that.  The polling interval changes 
>throughout the day in both directions.
>
><snip>
>
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