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

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

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Tim Deegan wrote:
>
> Not that I can remember.  You could try scattering printks in 
> hvm_latch_shinfo_size() to see if it's getting called at all,
> and in arch_set_info_guest() to see if it's calling
> update_domain_wallclock_time() like it should. 
>   
Thanks, I will add log into those functions to see...

Thanks
Annie
> Tim.
>  
>   
>> 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> [mailto:xen-devel-
>> bounces@lists.xensource.com<mailto:bounces@lists.xensource.com>] On Behalf Of ANNIE LI
>> Sent: 16 September 2010 09:31
>> To: xen-devel@lists.xensource.com<mailto: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
>>
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>>
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>>
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>>
>>     
>
>   

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