Messages in this thread | | | Date | 26 Oct 2006 05:24:30 -0400 | From | linux@horizon ... | Subject | 2.6.19-rc2 and very unstable NTP |
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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.) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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