Simon Arlott schreef:
The PPS thread should be realtime - the rest of the daemon doesn't.
This is a bit difficult to achieve within the code structure of gpsd.
The main program drops root privileges early, before it reaches the
point where devices are attached.
So when the pps monitor thread is created, the program already has
dropped privileges and the realtime priority cannot be set.
As said, in practice it does not seem to be a problem. The pps monitor
thread does a blocking wait on an RS232 line transition, so when it is
sleeping at elevated priority (because of the nice -10) it will most
likely get the CPU for long enough to read the time. After that, exact
timing is not critical anymore.
When bettar accuracy is required, it is better to get a
nanosecond-patched kernel anyway.
Rob
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