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[Xen-devel] Re: Clock Running Fast on Win7 DomU

We've tracked this down further an it seems to be an issue with the virtual 
HPET. Some difference between 3.4.2 and 4.0.1 results in Win7 clock running 
fast. The lower the programmed frequency the more accurate the Win7 clock is.

HPET frequency vs time for Win7 clock to tick off 60s:
1ms     60s
10ms   50s
15ms   46s

In Win7 the 'rate adjustment' column of the HalpHpetClockTable is zero for all 
frequencies. Our current working theory is that an issue at startup is causing 
the error calibration to fail or not happen resulting in larger errors at 
larger frequencies.

On Jun 14, 2011, at 9:05 AM, Tom Goetz wrote:

> Has any seen the following?
> The Win7 clock ticks of 60s in 47s. Reproducible 100% on multiple machines. 
> Happens on Win7, but not XP. This made me think of Viridian, but disabling 
> Viridian didn't change anything. Also happens with one or two CPUs in the 
> DomU. DomU VPUs are pinned to CPUs 0 -> 0, 1 -> 1, etc.
> Any ideas?
> DomU: Win7
> Dom0: 2.6.38 PVOPs, Ubuntu 11.04
> Xen: 4.0.1

Tom Goetz

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