Andrey Skvortsov <andrej.skvortzov@gmail.com> [Fri, 01 Jun 2018 12:21:37 +0300] rev 2171
use CLOCK_MONOTONIC instead of CLOCK_REALTIME for timer setup
CLOCK_REALTIME is a wall clock, that could change back and forth (user
changes system time, winter/summer time, NTP corrections and so on).
For real-time application CLOCK_MONOTONIC should be used, it doesn't
have such jumps.