Re: Time Skewing on Windows XP

[Suravee Suthikulanit <suravee.suthikulpanit@amd.com>]

On 3/12/2013 10:55 AM, Suravee Suthikulanit wrote:
> On 3/12/2013 4:13 AM, Paul Durrant wrote:
>>> -----Original Message-----
>>> From: xen-devel-bounces@lists.xen.org [mailto:xen-devel-
>>> bounces@lists.xen.org] On Behalf Of Suravee Suthikulpanit
>>> Sent: 12 March 2013 04:40
>>> To: George Dunlap; Jan Beulich
>>> Cc: xen-devel@lists.xen.org
>>> Subject: [Xen-devel] Time Skewing on Windows XP
>>>
>>> Hi,
>>>
>>> While I was investigating the following issue on Windows XP (both 
>>> 32-bit and
>>> 64-bit):
>>>
>>> * AMD NPT performance regression after c/s 24770:7f79475d3de7
>>> Reference:http://marc.info/?l=xen-devel&m=135075376805215
>>>
>>>
>>> On the latest source form xen-unstable, I ran into an issue where 
>>> the timing
>>> on the HVM guests skewing about 2x slower than the actual wall clock 
>>> time.
>>> This results in the system time slowing down. This is regardless of the
>>> cpufreq governor scaling. (I tried with both ondemand and performance).
>>>
>>> However, I don't see the same behavior on the Win7 HVM guests. Is 
>>> this a
>>> known issue. I assume that XP and Win7 uses different mechanism for
>>> keeping time (e.g. rdtsc vs. HPET)?
>>>
>> I think XP uses TSC and more recent versions of Windows use PM TIMER. 
>> Try booting XP with the /USEPMTIMER switch in boot.ini.
>>
>>    Paul
> Paul,
>
> That still doesn't help in this case.  I still see the WindowsXP guest 
> time skewing.  Also, I would not think the normal RDTSC skewing should 
> be this severe (0.5x comparing to the wall-clock time).
>
> Suravee
Ok, I found that the WinXP is actually using PMTIMER.  After inserting 
the debug messages, I can see that the function pmt_update_timer() is 
continuously being called by the handle_pmt_io().

Suravee
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