[time-nuts] Linux timekeeping / jiffy source
mikes at flatsurface.com
Fri Dec 3 03:17:52 UTC 2010
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
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
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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