NTPfiend fro75uk at yahoo.co.uk
Sun Mar 10 13:45:57 UTC 2019

OK, replies noted carefully.

 From 1200gmt on 10 March, I started running the ntpviz graph production 
(and uploading to the web site) hourly.   It appears that the nasty 
spikes are related to this task.    Yes, typo; the results are nice -n 
19 (user script so lower priority).

CPU governor, new territory for me.   R Pi documentation says the 
default is "ondemand":
which at first sight is a problem.   But, my R Pi has the upper and 
lower limits both at 700 MHz, so unless the mere task of ramping nowhere 
takes cpu oomph, there should be no difference from "powersave" or 
"performance".   I could edit /etc/init.d/cpufrequtils or possibly 
/etc/init.d/raspi-config (not the usual raspi-config) perhaps.

$ cpufreq-info
cpufrequtils 008: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to cpufreq at vger.kernel.org, please.
analyzing CPU 0:
   driver: BCM2835 CPUFreq
   CPUs which run at the same hardware frequency: 0
   CPUs which need to have their frequency coordinated by software: 0
   maximum transition latency: 355 us.
   hardware limits: 700 MHz - 700 MHz
   available frequency steps: 700 MHz
   available cpufreq governors: conservative, ondemand, userspace, 
powersave, performance
   current policy: frequency should be within 700 MHz and 700 MHz.
                   The governor "performance" may decide which speed to use
                   within this range.
   current CPU frequency is 700 MHz.
   cpufreq stats: 700 MHz:100.00%

To use ntpviz on a remote machine, I'd have to transfer the files. It 
appears simple (to me) to rsync from the ntpsec R Pi to somewhere else, 
with rsync being nice'd, maybe ionice'd and well throttled back with the 
--bwlimit option.

I'd like to experiment with the gps plots as well, which ISTR can impact 
heavily on the ntpsec R Pi significantly.   Maybe I could test 
overclocking. although that seems inherently unreliable to me and 
therefore a "bad thing" for timekeeping.
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