Re: [PATCH 3/4] Allow vif= to specify PCI address for each nic

[Don Slutz <don.slutz@gmail.com>]

On 06/16/15 12:14, Wei Liu wrote:
> On Tue, Jun 16, 2015 at 11:23:46AM -0400, Don Slutz wrote:
> [...]
>>>>>> which enables usage of xen-netback.
>>>>>>
>>>>>
>>>>> In any case, exposing HVM-only options to top-level vif configuration
>>>>> space doesn't look right.
>>>>
>>>>
>>>> There are already HVM-only options in vifs:
>>>>
>>>> ### type
>>>>
>>>> This keyword is valid for HVM guests only.
>>>> ...
>>>> ### model
>>>>
>>>> This keyword is valid for HVM guest devices with `type=ioemu` only.
>>>> ...
>>>>
>>>>> Why do you want to set bus and addr? The
>>>>> rationale should be stated in commit message.
>>>>
>>>>
>>>> That is why I said:
>>>>
>>>>>> This can help with Windows finding nics at boot time.
>>>>
>>>> Windows boot code is not as flexible as Linux.  Most versions of Windows
>>>> like to blue screen if the hardware changes enough.
>>>>
>>>
>>> Looks like you're trying to migrate a guest from VMWare to Xen. If
>>> device_model_args_new is sufficient please just use that.
>>>
>>
>> It works, but slowly because you are prevented from using the faster PV
>> nics.
>>
> 
> I'm a bit lost here. Aren't you trying to preserve the same nic
> configuration for Windows for compatibility reason (even if it's
> slower)? Why is PV network involved? How does this work?
> 

Yes, but there are 2 parts here:

1) boot time
2) run time

At boot time, windows wants devices to be where they were and to be
emulated.

At run time "newer" windows can switch to "Hyper-V enlightened I/O"
which as I understand it is like xen-netfront.  I.E. Windows will start
using xen-netback.

Looking at

http://www.techworld.com.au/article/303867/xen_3_4_0_released_more_client_device_hyper-v_integration/

It says "Also new is support for Microsoft's Hyper-V Enlightened I/O
interface."

And

https://msdn.microsoft.com/en-us/library/cc768521%28v=bts.10%29.aspx

says:

"Presently, both Windows Server 2008 and Windows Vista support Hyper-V
enlightened I/O and a hypervisor aware kernel via installation of
Hyper-V integration services. Integration components, which include VSC
drivers, are also available for other client operating systems."


Also last I knew Citrix does provide Windows drivers that (also?)
provided this faster access.


This may require additional configuration and/or software to be
installed on the windows disk.


I did not see a clear reason to prevent Windows from using the faster
access.

   -Don Slutz



> Wei.
> 
>>    -Don Slutz
>>
>>> Wei.
>>>