On 21/12/2012 19:51, Rick Jones wrote:
[]
Does the gpsd do anything every 5/3 minutes? Or put another way, can
you find a similar periodicity in the CPU utilization? If it does do
something interesting at that frequency and it involves a system call,
while the act of tracing would perturb things, you might find it in a
(timestamped) system call trace (strace) of the gpsd.
Perhaps the luck of process scheduling and the gpsd or some other
daemon holds-off the ntpd? (Raspberry Pi's are single-core systems
right?) Does the ntpd run at a higher (realtime?) priority than the
gpsd?
Might there be any other background dameons consuming more CPU on the
one system than the other?
rick jones
Thanks for your input, Rick. There's nothing obvious on the CPU plot
which correlates with the NTP offset plot, so I'm unsure whether they
are related. As an experiment, I've now removed NTP's dependency on
gpsd (although it didn't appear to be selected as a source, and was
/not/ the "prefer" source), and I will see whether the oscillation
re-occurs.
If I still see the problem, I will restart the system without gpsd enabled.
The systems are nominally identical, except that the oscillating system
has the serial data fed via GPIO pins, and the stable system is using
USB for the serial I/O, but that serial data isn't being used anywhere
(NTP relies on the LAN servers for its coarse time, and experimentally
it's now doing that on /both/ systems).
--
Cheers,
David
Web: http://www.satsignal.eu
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