[ntp:questions] chrony and ntp comparison-- ADSL hookup

Unruh unruh-spam at physics.ubc.ca
Fri Feb 22 01:49:38 UTC 2008

"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:

>Unruh wrote:
>> "David J Taylor" <david-taylor at blueyonder.neither-this-bit.nor-this-bit.co.uk> writes:
>>>Unruh wrote:
>>>>>- the default for min and max poll are 6 and 10 (IIRC), and not 4
>>>>>and 7
>>>>And so? Exactly how is this supposed to make a difference?
>>>It means that your tests are not carried out on an "out of the box" 
>>>configuration, and therefore perhaps less useful than they might otherwise 
>>>be.  It's possible that some servers would see min/maxpoll of 4 and 7 as 
>> And no "out of box" test is possible. Neither ntp ( althoug it is much
>> closer) or chrony are set up to do so. 
>> Right now I do not care what servers find abusive. I am using my own
>> server, so I decide what is abusive. I am not advocating these parameters,
>> I am using them to test ntp and chrony. ALL of the tests indicate that
>> chrony disciplines the clock about a factor of 2-3 better than does ntp.

>Testing ntpd and chrony using a local server or servers is not a very 
>realistic test of "real world" performance!

>Try configuring both with the same set of four to ten internet servers. 
>  Set up a stratum 1 server using GPS or a cesium clock as a reference 
>to serve as a standard to measure with.  Collect statistics for a month 
>or so.

>Then tell us what you learned.

You are starting to sound like the cigarette people when it was pointed out
that smoking might cause cancer.

I was trying to test the algorithms NOT the programs as a whole. 

I am not advocating that the world rush out and abandon NTP and alkl run
chonry. Too many problems. Chrony does not do refclocks. chrony does not
handle leap seconds. chrony runs only on Linux ( well a bit on a few others
but not many). However where chrony does run it "beats the pants off" ntp.
This suggests that the algorithm in chrony is a better clock discipline
algorithm than ntp's. Has this been tested extensively? No. Is it a
foolproof conclusion? No. But ALL the evidence at present is that chrony's
algorithm beats ntp's. If you believe that there are conditions under which
ntp's would beat chrony's it now becomes your duty to suggest why and
where. "You have not done enough tests" is the response of someone with a
completely closed mind.

I really do not care what you believe about ntp since you have zero data to
back up your position. I am not claiming that ntp fails. It is a robust,
well tested algorithm. It works and is certainly "good enough" for almost
everyone who uses it.  I am asking if it is the best we can do. My data
suggests it is not. 

Note the my latest test was NOT using a local server. It was a remoTE
stratum 1 server, over an ADSL hookup with a 16ms delay. 
It had 100 times the mean delay and 10 times or more the variance in that
delay of the "local" test. 
And exactly what would you expect to find if I ran it for a month rather
than a day? Would you really expect something about the chrony algorithm to
show up in  a month?  What? I suspect you have no idea whatsoever as to
what the chrony algorithm is so you could not if you wanted to.

And I used a GPS PPS as the reference source on the ADSL client to measure
the clock offset with.

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