[tor-bugs] #25052 [Core Tor/Tor]: [armhf, tor] strange "your system clock just jumped" warnings

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#25052: [armhf, tor] strange "your system clock just jumped" warnings
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     Reporter:  bundesgebaermutter  |      Owner:  (none)
         Type:  defect              |     Status:  new
     Priority:  Medium              |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core Tor/Tor        |    Version:  Tor: 0.3.2.9
     Severity:  Normal              |   Keywords:  clock,jumped
Actual Points:                      |  Parent ID:
       Points:                      |   Reviewer:
      Sponsor:                      |
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 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

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25052>
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