Re: [Xen-devel] More RTC issues with Win2k3

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.09.13 at 14:34, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 04/09/13 10:38, Jan Beulich wrote:
>> Which raises two questions: Does that specific version of Windows
>> not honor the WAET flags saying that REG_C reads are unnecessary?
>> Or does this only occur during very early boot (where iirc a first,
>> temporary RTC interrupt handler gets installed for a very brief period
>> of time that doesn't pay attention to the WAET flag)?
> 
> When the VM falls into the loop, it is still in text mode with "Starting
> windows..." and a block progress bar which is full.  This means that
> ntldr has finished loading the base drivers using int 13h.  From
> Xentrace, we do see that it is in 64 bit mode, so execution is probably
> right at the beginning of the kernel, even before switching the VGA mode.

So that might then be the early probing interrupt handler that I
had found they install transiently.

>>> I have attached xen-hvmctx from the affected domain, and do have one
>>> example of a VM in this loop so can poke for other state, if there are
>>> any sensible suggestions
>> The REG_A value says 64Hz for the periodic interrupt if I'm not
>> mistaken, so RTC_PF getting re-set between two iterations would
>> first of all hint at a significantly overcommitted system (such that
>> no two iterations of the loop can complete within 1/64 second).
> 
> This is part of our automatic testing.  There are two VMs (32 and 64bit
> variants) running the same set of tests, being basic lifecycle/migrate
> etc loops.  The hosts are not overcommitted in the slightest.

In which case, unless there's some scheduler anomaly involved, I
see no explanation for the behavior.

Not knowing what precise data Xentrace produces - does that include
any timing information? If so, what's the smallest delta between two
of these REG_C reads?

Jan


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