Re: Re: Does Xen also plan to move the back-end driver to the stub domain for HVM?

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

Liang Yang wrote:
> "QEMU has direct access to hardware", does this mean the QEMU device 
> model does not need to communicate with the native device driver which 
> is also sitting in dom0?
>

No, it means that it communicates with the native device drivers 
directly instead of going through another indirection layer (namely, the 
front and backend drivers).

Regards,

Anthony Liguori

> ----- Original Message ----- From: "Anthony Liguori" 
> <aliguori@us.ibm.com>
> To: "Liang Yang" <multisyncfe991@hotmail.com>
> Cc: <xen-devel@lists.xensource.com>
> Sent: Monday, March 19, 2007 11:20 AM
> Subject: [Xen-devel] Re: Does Xen also plan to move the back-end 
> driver to the stub domain for HVM?
>
>
>> Liang Yang wrote:
>>> Hi,
>>>
>>> Based on the roadmap on Xen summit, there is a plan to move QEMU and 
>>> let it run on the stub domain to improve HVM performance.
>>
>> Using a stub domain won't improve HVM performance.  It will improve 
>> accountability and scalability but running a single HVM guest 
>> shouldn't see any improvement.
>>
>>> However, comparing with QEMU device model, it will be much easier to 
>>> move BE driver and let it run in stub domain instead of dom0 as BE 
>>> part is running on the kernel space (QEMU is running on user space).
>>
>> Actually, this cannot make performance better since you're 
>> technically adding another layer of indirection in the picture.  
>> Within dom0, qemu-dm has direct access to the hardware.  Fortunately, 
>> the Xen BE/FE model is quite good performance wise so there shouldn't 
>> be a performance regression here.
>>
>>> but I'm little bit confused about the relationship between stub 
>>> domain and guest domain. Is the stub domain part of guest domain? 
>>> Does each guest domain have a stub domain which is created when the 
>>> guest domain is created?
>>
>> A lot of this is still being worked out.  From a user perspective, 
>> the idea would be that creating an HVM domain would be identical to 
>> how it's done today.  What happens under the covers though remains to 
>> be seen.
>>
>> Regards,
>>
>> Anthony Liguori
>>
>>> If the stub domain is part of guest domain, does porting device 
>>> model to stub domain compromise the orginial design purpose of 
>>> isoloated devide domain?
>>>
>>> Thanks,
>>>
>>> Liang
>>
>>
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>