[ntp:questions] Re: is there a way to "lock" the drift frequency

Tim Shoppa shoppa at trailing-edge.com
Mon Nov 17 12:50:05 UTC 2003


wayne <wayne at midwestcs.com> wrote in message news:<x4smkqvhvv.fsf at footbone.midwestcs.com>...
> Is there a way to "lock" down the pll frequency to some value around
> what is in the drift file?
>
> The two most common causes of this are when my ADSL line gets
> saturated for a long period of time (usually due to people trying to
> download my entire 2GB website)

For this case, a patch to NTP's "MAXDISPERSE" value might do some good.
(Actually, it's peerdelay/2 + peerdispersion that this is compared to.)
By lowering it you could cause your peers, when they don't respond
quickly (and you would set the threshold to be a chunk above "normal"
network load) to appear unreachable.  Your machine will keep it's
nominal frequency and "drift" until the network load reduces and you
trust it again.  When the delay comes back down and they are deemed
reachable, then you meet the problem found in the "pinball" thread, though.
(A case of "a hole in the bucket"!)

MAXDISPERSE is in include/ntp.h in the NTP source tree.

If you really don't like tweaking MAXDISPERSE you could add another
test based only on peerdelay in ntp_proto.c.  It could be added near
test 8, in particular.

Tim.



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