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    SubjectRe: time warps, I despair
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    >>>>> "IM" == Ingo Molnar <mingo@pc5829.hil.siemens.at> writes:
    In article <Pine.LNX.3.93.961101175301.3565B-100000@pc5829.hil.siemens.at>
    Ingo Molnar <mingo@pc5829.hil.siemens.at> writes:

    IM> On Thu, 31 Oct 1996, Ulrich Windl wrote:
    IM>
    >> So what's the effect? From time to time the clock offset jumps for
    >> some amount always less or equal to what's worth one tick (i.e.
    >> offset jumps around from -5ms to 5ms when synchronized). [...]
    IM>
    IM> this could be caused by a 'lost jiffy'. Lost jiffy is a timer hardware
    IM> interrupt that misses us completely. Under normal hardware circumstances
    IM> (no APM, etc.), this is only possible if there is a cli()/sti() pair that
    IM> lasts for more than 10 millisec.
    IM>
    IM> You can totally eliminate the Pentium stuff by turning APM support on in
    IM> the kernel (or commenting out the last few lines in time.c), thus the PIC
    IM> timer is used as high precision timing offset source.

    Sorry, but I think this is NOT only pentium related - It might be a more
    general problem!

    Ulrich's graphs show spike interval of 10-12 minutes if I read these graphs
    correctly. On my system I can see a similar spike interval of about
    120 minutes.

    My system is a i486-DX2/66 running on a ASUS-SP3G motherboard with
    xntpd-3.4z and linux 2.0.14. I see this anomaly for about two years
    now (since kernel 1.1.3x or so). Time source is a cheap DCF77 receiver
    on a serial port. Before you ask: There are no processes which runs every
    even hour like cron or so.

    - - Andreas

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    --
    Andreas Koppenhoefer, Student der Universitaet Stuttgart, BR Deutschland
    Franz-Schubert-Str. 2, 97616 Bad Neustadt; Phone +49 9771 7943, Fax/Data 7947
    <akoppenhoefer@schweinfurt.netsurf.de>,<koppenas@informatik.uni-stuttgart.de>
    <Andreas.Koppenhoefer@studbox.uni-stuttgart.de>; PGP-Key available at
    URL <http://www.informatik.uni-stuttgart.de/menschen/ako/impressum.html>

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