[armhf, tor] strange "your system clock just jumped" warnings

I recently upgraded to 0.3.2 because 0.3.0 won´t be supported beyond the end of this month anymore. The warning first occured in 0.3.1 by the way. The tor relay is running on a bananapi box on Debian Jessie and a custom grsec enabled kernel 4.8 (soon to be upgraded to stretch).

[https://atlas.torproject.org/#details/15841A96CA5C1171985A9565BF7CDDFE2BF8E91E]

At first I thought the new "diff-cache" consumes too much cpu and causes the clock jump warning. But even if I set the consensus age to one second, the warning won´t disappear. They can be found one or two times per hour in the syslog saying the clock is 100-500 (forward) seconds off.

A ntp client is running to keep the clock up to date. So I began to record the clock skew into a rrd and queried(*) the local network ntp server every ten seconds. The average is 1.6 milliseconds so far.

Maybe the experts have some ideas. Thanks for your time :)

---

Collected information can be found on the webserver - please don´t mind the self-signed certificate:

The clock skew graph: [https://bundesgebaermutter.ddnss.eu/graphs/torinfo4.png]

CPU usage (tor is limited to one core at the moment): [https://bundesgebaermutter.ddnss.eu/graphs/torinfo5.png]

An excerpt of tor´s debug log around a clock jump: [https://bundesgebaermutter.ddnss.eu/torlog.sample1.gz]

(*) = ntpdate-debian -q -p2 ntp-server-ip-address

Trac:
Username: bundesgebaermutter