[time-nuts] Linux timekeeping / jiffy source

[Robert Darlington]

Are you running ntp, and if so, did you kill the old drift file?

On Dec 2, 2010 8:18 PM, "Mike S" <mikes at flatsurface.com> wrote:

Anyone familiar with Linux kernel timekeeping?

I've recently upgraded a server to an AMD 890FX/SB850 based motherboard.
After doing so, I observed a large (in time-nut terms) inconsistency in
system timing, as seen in the rate of the system's Time Of Day clock.

Sync'ing to a local GPS locked NTP server, I see up to an 80 ppm spread
between reboots, which I've documented at
http://www.flatsurface.com/AMD_SB850/index.html . I'm running kernel 2.6.32
(Debian squeeze).

I think that kernel timekeeping ("jiffies") are linked to the "8254" timer
in the SB850 south bridge, but maybe it's the HPET in the 890FX north
bridge. Anyone know how to tell which the kernel is using for timekeeping?

Also, is it possible to restart the Linux kernel without a full reboot
(avoiding BIOS initialization), to see if it's a kernel or BIOS issue? I
don't believe a simple change of runlevel restarts the kernel from scratch.

I haven't seen this inconsistency on previous Intel or Serverworks based
motherboards, but I've seen this behavior on 890FX/SB850 motherboards from
two different manufacturers (although I think both use Award BIOS).

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