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SubjectRe: Clock inaccuracy seen on NVIDIA nForce2 systems
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On Wed, 2004-10-13 at 21:27, linux@horizon.com wrote:
> > The system is running 2.6.9-rc4 and has been up for 2 days. I'm showing
> > an offset of -32 seconds and growing.
>
> That's -185 ppm (parts per million) error, or -0.0185%.
>
> Typical cheap quartz crystals are +/- 100 ppm, but there are some cheaper
> than that, and ceramic resonators like
> http://www.ecsxtal.com/cerares.htm
>
> I know Dave Mills learned from experience that the original +/-100 ppm
> specs in NTP weren't wide enough and he had to change it to cope with
> +/-500 ppm error in some clocks.
>
> It *could* just be your motherboard's clock source.

possible but....

a) When I boot without 'acpi_skip_timer_override' and I fall back to
using ExtINT for the timer there is no drift.

b) I rebooted and set FSB spread spectrum to 1.0 and let the machine run
over night. In 10 hours of uptime I'm off -45 seconds and growing. This
is -0.125%. So clearly having spread spectrum enabled does affect the
clock.

Thanks

Jesse

--
Jesse Stockall <stockall@magma.ca>

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