Re: [Xen-devel] Time Skewing on Windows XP

[Suravee Suthikulanit <suravee.suthikulpanit@xxxxxxx>]

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@xxxxxxxxxxxxx [mailto:xen-devel-
> > > bounces@xxxxxxxxxxxxx] On Behalf Of Suravee Suthikulpanit
> > > Sent: 12 March 2013 04:40
> > > To: George Dunlap; Jan Beulich
> > > Cc: xen-devel@xxxxxxxxxxxxx
> > > 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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