[ntp:questions] Hopelessly broken clock?

Jason Rabel jason at extremeoverclocking.com
Sun Nov 16 14:22:22 UTC 2008


This is *probably* caused from EIST and/or C1E being enabled in your BIOS.
These features dynamically adjust the speed of your CPU (and voltage)
according to the CPU demand. You can try to disable them and see if things
stabilize, if they do then you know what the culprit is.

If you really want EIST & C1E enabled (or just want to see if you can get a
more stable time source), check which time source you are using in Linux,
and if possible try changing to a different one.

# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
(what you are currently using will be here)

# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
(what you can choose from will be here)

I'm running CentOS 5 on my system and the only clock source I have available
is jiffies. Newer kernels should give you options like: acpi_pm jiffies hpet
tsc pit.


> I'm trying to set up ntp on a new Core2 Duo box running Fredora Core9.
> It appears that it's local clock runs several seconds an hour fast.  I'm
> basing this on running ntpdate against the existing box I have running
> ntp with pps.  It reports skewing the clock by seconds even after just
> a few minutes.

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