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    Subject2.6.19-rc2 and very unstable NTP
    There have been a bunch of changes to timekeeping since 2.6.17, and I've
    noticed that, with 2.6.19-rc2 + linuxpps, I'm getting some impressively
    unstable oscillations in the local time. +/- 350 us, when, given a
    good quality local PPS source, it should be wiggling +/- a few us.
    And the shape of the curves is not "wander" but "overcorrecting wildly".

    It's sort of series of exponential decay curves, but each one overshoots
    by 100%, and then before it fully flattens out, starts surging in the
    other direction. (Actually, the overshoot amplitudes fluctuate
    erratically, too.) As best I can render it in ASCII art:


    * * *
    * *
    * *
    * *
    * * * *

    * *
    * *
    --------------*----------------------*-----------
    * *

    * * * *
    * *
    * *
    * *
    * *

    600-700 us p-p, with 2200-2400 s per full cycle.

    It looks like ajtimex() isn't doing what NTP is expecting,
    leading to loop instability.


    I'm going to git bisect this, although it's a bit time-consuming
    waiting to see if things will settle own cleanly after each reboot.
    And some of the patches have been anything but one-liners, so
    that's not necessarily a direct pointer to the problem.

    I know there have been a number of reports of ntp timekeeping
    problems with 2.6.18. Has there been any progress already?

    (Local system: AMD64 uniprocessor, 2.6.19-rc2+linuxpps kernel,
    NTP 4.2.2, Acutime 2000 GPS clock + PPS input.)
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