Richard,
Carefully read my pouty lips. Time constant, time constant. When the
time constant is forced small, switching to a long poll interval is
unstable. Really, really. That's the design consideration. You might be
able to get away with doing that in fact, but that's not the design intent.
Dave
Richard B. Gilbert wrote:
David L. Mills wrote:
David,
The poll intervals are not managed as you think. The basic
consideration is for the discipline loop time constant, which
determines the optimum poll interval. The design goal is to move it to
the highest value consistent with the anticipated clock frequency
wander. A secondary consideration is that the loop not be undersampled
should the timing source change. You have constrained the poll
interval and time constant when you specify a maxpoll for a source
that happens to synchronize the client and that forces all the others
to the same value in case one of them is selected.
There small gain in performance when forcing the poll interval to
smaller values as against letting the algorithms optimize for ambient
conditions. If you are trying to squeeze the optimum performance when
doing that, the cost is all the sources are constrained as well.
Dave
David J Taylor wrote:
Richard B. Gilbert wrote:
[]
The reference implementation of ntpd contributes to the deluge in a
small way! Running a Motorola Oncore as a reference clock causes my
home server to query its internet servers every 16 seconds. It's
nothing I would do by choice; they serve only as a sanity check on my
Oncore reference clock There does not appear to be any way of
turning this feature off short of modifying the code.
Agreed. I would like to have my client PCs poll their two LAN
servers at 64s and one Internet server at 1024s (also as a sanity
check), but it seems that if any LAN server is set to 64s the
Internet servers are also polled at 64s intervals.
David
I realize that the poll intervals are carefully selected for optimum
performance when only network servers are involved but do those
considerations really require that network servers be polled every
sixteen seconds when a GPS reference clock is the synchronization
source? Wouldn't it be sufficient to poll the network servers
immediately if it is considered necessary to switch synchronization
sources? After all, they would not normally be polled at intervals of
less than 64 seconds even if they were the sole time source!
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