Re: [Qemu-devel] About qemu emulation speed (a question) and supported OS

[Anthony Liguori <aliguori@us.ibm.com>]

Mark Williamson wrote:

>>>No, I got the impression that Fabrice was taking about virtualization the
>>>way VMware, old plex86, and vmbear (new FOSS x86 virtualizer in the
>>>works) do it.
>>>      
>>>
>>The x86 cannot be "virtualized" in the Popek/Goldberg sense, so there's
>>a couple of fast emulation techniques that are possible.  Other than a
>>hand coded dynamic translator, I reckon qemu + kqemu is about as good as
>>it can get (unless I'm missing something here).  Do you have
>>    
>>
>
>Well, VMware does manage direct execution of some kernel code, I believe.  
>VMware's real super-cunningness is doing this as much as they can, instead of 
>emulating all the stuff.  That said, I think with suitable optimisations 
>emulating all the kernel code could be acceptable.
>
>The unfortunate thing is that the guest can still tell it's in a VMware 
>machine (I'm not clear how) so it's not really *full* virtualisation, it's 
>just about epsilon away from it :-)  VT / SVM will solve this properly.
>  
>
I reckon kqemu has this same problem... Technically, even in ring 3, if 
you run natively, you violate the Popek/Goldberg requirements because of 
cpuid.  It's just not possible to trap it but it shouldn't matter for 
most software.

>They have a (crazy but cool) idea that they'll one day be able to live-migrate 
>(i.e. without more than a few hundred ms downtime) virtual machines between 
>L4 hypervisors and Xen hypervisors.
>  
>
Yeah, how cool is that :-)

Regards,

Anthony Liguori

>Cheers,
>Mark
>
>  
>
>>>>FWIW, Xen is already using QEMU in this way.  It would be very neat to
>>>>see this technique applied to a Type II VMM.
>>>>        
>>>>
>>>Do you have any details on this?
>>>      
>>>
>>Mark did a really good job of summarizing the current architecture.
>>
>>Regards,
>>
>>Anthony Liguori
>>
>>    
>>
>>>>Regards,
>>>>
>>>>Anthony Liguori
>>>>
>>>>
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>>>>
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>>    
>>
>
>  
>