NTPfiend fro75uk at yahoo.co.uk
Tue Mar 12 18:08:28 UTC 2019

Following on from recent suggestions, I experimented a bit.

First: Instead of producing 7-day ntpviz graphs, I just went for 24 hour 
graphs.   This reduced the nasty spikes to about 40% of previous, better 
but not acceptable.

Second: the R Pi (hardware 0010) was overclocked at 800 MHz (normal is 
700 MHz) and the governor set to fixed speed of performance.   I also 
tweaked /boot/config.txt
     added nohz=off
     commented out #dtparam=audio=on
     corrected gpu_mem=0 to gpu_mem=16
No obvious difference [...but]

Third: ntpstats were slowly moved (hourly cronjob) to another machine 
(an Odroid HC-2) running ntpsec (which compiled easily and quickly).   
This has been running over 24 hours now 
http://www.goldhill.uk/ntpvizplots/index.html and has completely solved 
the problem.   No nasty perfomance hits and the R Pi has settled down 

[...but] previously any small offset changes or jitter were rendered 
invisible by the spikes, now much more visible with the much reduced 
range of the y-axes.   I'm wondering what else I will now notice !

For now, it seems like a decently performing setup.   I'm still looking 
for ntploggps to add GPS, plus temperature graphs sometime.   I probably 
ought to let it settle down for a while beforehand.

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