[ntp:questions] Tighter regulation?
david at ex.djwhome.demon.invalid
Sat May 25 12:57:27 UTC 2013
Mischanko, Edward T wrote:
> I would modify the current algorithm with an exception that if offsets
> exceed 1 millisecond for more than one polling cycle, then, polling will be
> reduced by one interval, else, continue normal operation.
Whilst I still think the OP is trying to make the statistics look good,
rather than have good time keeping, I can sort of see two feature
1) a tinker option to specify an assumed maximum jitter, which will
allow the user to put in a long term jitter statistic for their system,
rather than having ntpd work it out for itself.
2) a tinker option for a panic level of offset, where, it is assumed to
be so improbable, given the specific noise statistics of the actual
system, that it should immediately be considered to be due to a local
clock frequency error. Measurement noise is often non-gaussian, so it
unlikely to be safe to make this a fixed multiple of the value in item
(1). If this is to be used without filtering by the minimum delay
filter, it will need to be a lot higher than the filtered value, as the
minimum delay filter will take out most one off spikes in offset.
I am not volunteering to write the code for these, and I do have concern
that an urban folklore will develop in which in become it becomes common
advice to set them excessively low.
However, I still feel that, if the underlying problem is clock frequency
drift, the primary fix is to address the cause of that drift, and the
stop gap solution is to reduce maxpoll. If it is almost anything else,
the offset changes do not indicate a timekeeping error and should not be
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