[ntp:questions] ntpd and High resolution timer

Unruh unruh-spam at physics.ubc.ca
Tue Apr 29 18:12:52 UTC 2008

hal-usenet at ip-64-139-1-69.sjc.megapath.net (Hal Murray) writes:

>>I am using NTPd and I have guessed that it uses the High Resolution Timer,
>>brought to the linux kernel since the 2.6.16 release.
>>Does anyone know if it said somewhere in the documentation or any other
>>"official" source, a trusty one.

>ntpd "just" calls the kernel.

>Recent Linux kernels have several modules for timekeeping.
>Look in .../Documentation/kernel-parameters.txt

>I think the normal one is TSC.  (At least on the machines I've
>worked with.)  The TSC calibration code is buggy.  It doesn't
>quite get the same answer each time.  (If you patch the kernel
>to call it several times, you will get several different answers.)

>It's very close, but it's off by enough to confuse ntpd.  In
>particular, it will introuduce a startup transient after each
>roboot until ntpd figures out the new drift value.  It took my
>system several/many hours to do that.

>I haven't seen that problem since I added
>  clocksource=acpi_pm
>on the boot time parameters.

What version of the kernel do you have? 2.6.17 does not have clocksource
parameter or an acpi_pm option. Is there anywhere where these different
clock parameters are defined?

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