[ntp:questions] PPM steps vs kernel PPS

A C agcarver+ntp at acarver.net
Fri Feb 17 07:29:00 UTC 2012

Since I was forced to restart ntpd I decided to play with flag3 now that 
I have all the statistics being generated.  I notced some behavior I 
don't quite understand.  If I have flag3 disabled, I see that the clock 
adjustment in PPM slews slowly in steps of 0.001 PPM as it tries to keep 
the clock offset near zero.  I usually see this when the furnace turns 
on and shifts the room temperature so I know the root cause of the shift.

Now, if I enable flag3, kernel PPS is engaged (seen in the main log 
file).  At this point I see that the clock adjustment will hold a steady 
value for a while and then suddenly change by some amount usually over 
0.010 PPM instead of the finer steps of 0.001 like in the previous case.

Is this normal behavior when kernel PPS is enabled or has something gone 
wrong with my configuration?

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