inaccurate system clock when HZ != 100

[Eric Cooper <ecc@cmu.edu>]

I've been running vanilla kernel.org kernels on my PowerMac 7600.
With one of the recent 2.6.14-rcX versions, the default value for HZ
could be set to 250 or 1000 for non-interactive machines, with 250
being suggested.  So I started running that version, and I noticed
that my system clock no longer tracked my hardware clock.

Even a few minutes after doing
    $ ntpdate -b pool.ntp.org
    $ hwclock --utc --systohc
the system clock had started falling behind.

Finally I rebuilt the kernel with the old HZ=100 and the problem has
gone away.

Not sure whether this is a kernel problem or an interaction with NTP,
etc., but my x86 machines have HZ=250 and don't exhibit this problem,
so it seems to be powerpc-specific.

-- 
Eric Cooper             e c c @ c m u . e d u