[ntp:questions] NTP vs chrony comparison (Was: oscillations in ntp clock synchronization)

Danny Mayer mayer at ntp.isc.org
Thu Jan 31 02:27:56 UTC 2008


Unruh wrote:
> "David L. Mills" <mills at udel.edu> writes:
> 
>> David,
> 
>> We can argue about the Hurst parameter, which can't be truly random-walk 
>> as I have assumed, but the approximation is valid up to lag times of at 
>> least a week. However, as I have been cautioned, these plots are really 
>> sensitive to spectral lines due to nonuniform sampling. I was very 
>> careful to avoid such things.
> 
> But the "lines" I am refering to are not artifacts, they are there because
> of the way the computer is used. -- the temp fluctuations caused by people
> running the machine daily, except on weekends. These are not part of any
> "random walk" process. They are real jumps in the drift rate of the
> machine, large jumps, and definitely not random.
> 

Well of course. You are running Linux and losing interrupts. FreeBSD and 
friends don't suffer from that problem. I seem to remember setting 
HZ=100 mostly eliminates that problem, at the price of rebuilding the 
kernel.

Danny



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