[ntp:questions] NTPD can take 10 hours to achieve stability

David Lord snews at lordynet.org
Wed Apr 20 09:26:28 UTC 2011


unruh wrote:
> On 2011-04-19, David Lord <snews at lordynet.org> wrote:
>> unruh wrote:
>>> On 2011-04-19, David Lord <snews at lordynet.org> wrote:

.....

>>>> When I first compared chrony with ntpd there was no contest
>>>> but more recent experiments with chrony had periods of
>>>> severe instability much worse than ntpd.
>>> More recent means what? What version of chrony? (there was a bug found
>>> in the past two weeks that was introduces a few months ago which did
>>> result in instability) 
>> More recent than  November 2009.
>> Probably between Dec 2009 and Jan 2010 and p4x2400c.
>>
>> chrony 1.23
> 
> OK well before that change. 
> 
>>
>>>> P4X2666 with chrony
>>>> <http://www.lordynet.org.uk/mrtg/stats/>
>>> Not at all sure what I am supposed to see. I have no idea what the graph
>>> axes represent?  What is 1.1k 
>> X-axis is in hours
>> Y-axis is offset in us so 1.1k = 1100us
> 
> WOW. What kind of network are you attached to? Even on an ADSL link
> through the phone company, I
> was getting in the tens of usec (not ms) as the offsets of chrony.
> (checked by a gps receiver attached to the local computer).

I'm on ADSL-1 with 2 Mbit/s down and 288 kbit/s up. Latency
is what BT delivers and has been as low as 12ms up to 50ms or
more but mostly it's about 18ms to nearest sites (when exchange
gets near capacity the latency jumps up by 15ms or more same as
when interleave is enabled on ADSSL-2).

Although the peaks of the graph are at about 1ms the stats
have "System time" mostly being in the 10s of usec.

> 
> And what is it about the graph that makes you believe you are seeing
> instability. 

There is nothing in that session but later graphs now
wrapped (as in loops around after a year) showed much
worse offset variations than the systems using ntpd at
which point I went back to using ntpd.


David

>> Next experiment is to couple up the GPS again but if you
>> click on the ME6000 in the current stats the yearly graph
>> for Sep/Oct/Nov was when I last had the gps connected.
>>




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