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

On Jun 27, 2011, at 8:56 AM, Tim Deegan wrote:

> Hi Tom,
> At 09:18 -0400 on 16 Jun (1308215917), Tom Goetz wrote:
>> 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
> Have you been able to reproduce this on 4.1 or 4.2-unstable?  The Win7
> clock seems to be running at the right speed for me on unstable, just by
> booting win7 (sp1, 64-bit) and bringing up the desktop clock.  Or do I
> need to do something in particular to change the granularity to 1ms?
> Tim.
>> 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.

I resolved the issue. Our brand new Qemu from upstream was emitting interrupts 
for the PIC. The extra timer interrupts were making time go faster.

Thanks for replying.

Tom Goetz

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