2012/4/7 Steven D'Aprano <st...@pearwood.info>: > Victor Stinner wrote: >> >> 2012/4/7 Janzert <janz...@janzert.com>: >>> >>> On 4/5/2012 6:32 AM, Victor Stinner wrote: >>>> >>>> I prefer to use CLOCK_MONOTONIC, not because it is also available for >>>> older Linux kernels, but because it is more reliable. Even if the >>>> underlying clock source is unstable (unstable frequency), a delta of >>>> two reads of the CLOCK_MONOTONIC clock is a result in *seconds*, >>>> whereas CLOCK_MONOTONIC_RAW may use an unit a little bit bigger or >>>> smaller than a second. time.monotonic() unit is the second, as written >>>> in its documentation. >>> >>> I believe the above is only true for sufficiently large time deltas. One >>> of >>> the major purposes of NTP slewing is to give up some short term accuracy >>> in >>> order to achieve long term accuracy (e.g. whenever the clock is found to >>> be >>> ahead of real time it is purposefully ticked slower than real time). >> >> I don't think that NTP works like that. NTP only uses very smooth >> adjustements: >> >> ""slewing": change the clock frequency to be slightly faster or slower >> (which is done with adjtime()). Since the slew rate is limited to 0.5 >> ms/s, each second of adjustment requires an amortization interval of >> 2000 s. Thus, an adjustment of many seconds can take hours or days to >> amortize." >> http://www.python.org/dev/peps/pep-0418/#ntp-adjustment >
> That is incorrect. NTP by default will only slew the clock for small > discrepancies. For large discrepancies, it will step the clock, causing the > time to jump. By default, "large" here means more than 128 milliseconds. > > Yes, milliseconds. > > http://www.ntp.org/ntpfaq/NTP-s-config-tricks.htm#AEN4249 We are talking about CLOCK_MONOTONIC. Steping is disabled on this clock. Victor _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com