Re: how to keep time of windows pvhvm synchronized with host after resuming

[ANNIE LI <annie.li@oracle.com>]

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> More specifically, they're what you should add to the current Xen system
> time to get the wallclock time (they can change over time as the system
> time drifts).  I'm surprised to hear that they're zero.  Even if dom0
> isn't updating them (which IIRC pv-ops dom0 doesn't) they should have
> been set from the RTC at boot time.  It's possible that your domain's
> shared-info page is in the wrong word size - if you haven't set up a
> hypercall page or set HVM_PARAM_CALLBACK_IRQ since the domain was
> created (i.e. since restore) it might be wrong. 
>   
Maybe this is not a problem of shared-info page.
The problem is wc_sec and wc_nsec does not change until i modify 
wallclock time of windows vm manually.
If i do not change the wallclock, wc_sec will keep the same value. For 
example: the initial value of wc_sec is zero,
then it changes to 0x4c64da92 if i change wallclock, 0x4c64da92 is about 
40 years since 1970.

I am using xen3.4 for test, any patch i missed?

Thanks
Annie
> One problem with using wc_[n]sec to get the wallclock time is that the
> usual Xen way to get the system time is to interpolate it from the RDTSC
> value and the per-vcpu time info, but in a HVM guest the OS may have
> changed the TSC offset to something that the driver can't figure out.
> The Citrix PV drivers use the HVMOP_get_time hypercall to get the system
> time instead; that hypercall is in xen-unstable but not the 4.0 branch.
>
> If you're using a linux guest with Stefano's pv-on-hvm patches then I
> think you should be able to read the PV system time as normal.
>
> Tim.
>
>   
>>   Paul
>>
>>     
>>> -----Original Message-----
>>> From: xen-devel-bounces@lists.xensource.com [mailto:xen-devel-
>>> bounces@lists.xensource.com] On Behalf Of ANNIE LI
>>> Sent: 16 September 2010 09:31
>>> To: xen-devel@lists.xensource.com
>>> Subject: [Xen-devel] how to keep time of windows pvhvm synchronized
>>> with host after resuming
>>>
>>> Hi
>>>
>>> When the virtual machine is resumed from suspend, the guest
>>> operating
>>> system's wall-clock time remains at the value it had at the time of
>>> the
>>> suspension. For linux pvm, we can avoid resolve issue by setting
>>> independent_wallclock=0. However, HVM(or PVHVM) does not support
>>> this
>>> feature.
>>>
>>> I did some investigation on how to implement this in windows
>>> para-virtualization driver. In \include\xen\interface\xen.h, there
>>> are
>>> several variables about timer such as: wc_sec and wc_nsec, and
>>> vcpu_time_info struct. It is very strange, wc_sec and wc_nsec is
>>> always
>>> zero for my windows vm with para-virtualization driver.
>>> Vcpu_time_info
>>> only contains time info for specific vcpu. Should i use those
>>> variables
>>> to get accurate time for VM? Is there any corresponding source code
>>> or
>>> algorithms available now? Is it safe to simply update vm time after
>>> resuming?
>>>
>>> Citrix 5.6 Windows para-virtualization driver will notify windows
>>> kernel
>>> time change after resuming, and resumed windows vm with Citrix pv
>>> driver
>>> can keep it's time synchronized with host. Would you like to give me
>>> some clues about how to implement this?
>>>
>>> Any help is greatly appreciated.
>>>
>>> Thanks
>>> Annie
>>>
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@lists.xensource.com
>>> http://lists.xensource.com/xen-devel
>>>       
>
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>
>
>   

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