[ntp:questions] Thoughts on huff and puff
david at ex.djwhome.demon.co.uk.invalid
Sat Oct 11 10:09:07 UTC 2008
I had cause to look at tinker huffpuff recently and a number of things
1) It is applied globally, and that seems to include reference clocks,
including the local clock (which you can expect to find on most real
world configurations, even though it is often inappropriate for them).
That means that the presence of a reference clock as a reference, or the
use of another source on the same LAN may artificially depress the
estimate of the minimum delay.
Ideally it should be done per association, and if that is too expensive,
one should be able to opt servers into the the mechanism, which one
would, probably, only then do for ones LAN servers. It should not be
applied to reference clocks in general and certainly should not be
applied to the local clock.
2) Its method for determining the sign of the correction is
oversimplistic. It would probably work if the actual clock error was
small, but, as we've seen discussed recently, ntpd handles real world
startup and temperature change transients poorly, which could result in
huff and puff trying to increase the error.
In many cases where huffpuff would be useful, one knows that the
asymmetry is overwhelmingly in one direction and there needs to be a way
of conveying that information.
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