From mboxrd@z Thu Jan  1 00:00:00 1970
From: Suravee Suthikulanit <suravee.suthikulpanit@amd.com>
Subject: Re: Time Skewing on Windows XP
Date: Tue, 12 Mar 2013 10:55:03 -0500
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To: Paul Durrant <Paul.Durrant@citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>, Jan Beulich <JBeulich@suse.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
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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