[chrony-dev] rtc under chrony has large fluctuations on some machines.

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

 have been looking at the offsets that chrony is reporting for the rtc
measurements. On both of the machines on which I have the new git chrony (
with the rtc patch) and one of the old machines ( without the patch) chrony is
reporting large fluctuations ( of order 10ms) in the offset readings of the
rtc clock. On other of the machines, the fluctuations are more like 100usec. 
I am not sure if this is due to the recent change in the way chrony is reading
the rtc ( ie doing another select wait and then a read, instead of two reads
with the second on a blocking read). 
I will do some more investigation to try to see what is going on.

It is of course not clear that getting the rtc to under 10ms is really
important, since the rate change with the computer switched off (cold crystal) is probably
larger than that needed to produce a 10ms offset even with chrony's attempt to
do rate estimation ( on a hot working machine) (a 1PPM rate change due to the
machine being cold would produce 10ms drift in 3hr, and chrony's fast
convergence means this is not that important as it will be corrected quickly
on starting chrony.) But it would be nice to get the "best possible".



--
William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology |     unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1     |      and Gravity       |  www.theory.physics.ubc.ca/

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