[ntp:questions] NTP vs chrony comparison (Was: oscillations in ntp clock synchronization)
unruh at physics.ubc.ca
Thu Jan 31 17:07:45 UTC 2008
On Wed, 30 Jan 2008, Danny Mayer wrote:
> 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.
No they are not lost interrupts. They are NOT jumps in the offset, they are
jumps in the frequency, which will last for a few hours and then jump back.
Lost interrupts do not act like that-- they would jump the offset by 10ms
(or 4ms) which is definitely not happening. Andit is hard to gain
William G. Unruh | Canadian Institute for| Tel: +1(604)822-3273
Physics&Astronomy | Advanced Research | Fax: +1(604)822-5324
UBC, Vancouver,BC | Program in Cosmology | unruh at physics.ubc.ca
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