ntpd struggling to keep up - how to fix?
torfinn.ingolfsen at broadpark.no
Sun Feb 21 09:02:30 UTC 2010
On Sun, 21 Feb 2010 16:08:23 +1100
Peter Jeremy <peterjeremy at acm.org> wrote:
> That's definitely not good - though it's marginally better than before.
> I have checked on a local machine and the timecounter frequency definitely
> needs to be adjusted in the opposite direction to the ntpd drift.
> I think I see the problem: I suggested 3579545Hz - 2500ppm, which
> gives an ACPI frequency of 3570596Hz. There was some miscommunication
> and you have set an ACPI frequency of 3577045Hz which is 2500Hz (or
> 698ppm) lower. The drift reported by the time resets has gone from
> +1930ppm (14.5s in 2:05:17) to +1233ppm (8.4s in 2:20:06) - which is
> 697ppm - fairly close to the change you made. (The PLL is running
> at +500ppm so the actual clock offset is 500ppm more than the "time
> reset" reports suggest.
Very good info, it helps me understand more. Thanks!
> Having re-checked my maths, using both your "time reset" results, can
> you please try:
> sysctl machdep.acpi_timer_freq=3570847
Ok, trying that now:
root at kg-f2# sysctl machdep.acpi_timer_freq=3570847
machdep.acpi_timer_freq: 3577045 -> 3570847
root at kg-f2# /etc/rc.d/ntpd stop
root at kg-f2# rm /var/db/ntpd.drift
root at kg-f2# /etc/rc.d/ntpd start
> That should result in a drift of close to zero (well within NTP's
> lock range of +/- 300ppm).
> No. Once ntpd decides to continuously step, something is broken.
Aha, very good to know.
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