Re: [Xen-users] VGA passthrough with Xen 4.3 and xl toolstack - performance degradation resolved?

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 03/12/2014 03:42 PM, H. Sieger wrote:
> Thanks for the reply! Good to know the old ATI patch still works with
> Xen 4.4.
If you are talking about the patch I think you are talking about, IIRC 
that was a patch for primary passthrough. This side-steps some of the 
problems of lack of reset by POST-ing the VBIOS in domU, so VBIOS gets 
the card into a state where the driver knows what to do with it.
> Unfortunately I use a Nvidia Quadro card for VGA passthrough and can't
> test it easily. However, some users on the Xen VGA passthrough how-to I
> posted on the Linux Mint forum have reported problems. I usually advise
> to use the xm toolstack as that doesn't run into issues with ATI
> graphics cards, but it doesn't work with Windows 8.1 guests.
I'm still not sure where you got the idea that xm stack works any better 
when it comes to ATI passthrough and resetting. Neither tool stack in 
4.3.x resets the ATI cards, and this results in the card being passed to 
domU the second time around in an unexpected state which makes the 
driver fall over.
> I really wish someone would integrate the ATI patch into a Xen release
> and be done with it. Though I've never tried it, I've seen people apply
> the patch and it seems to solve the problem.
I'm pretty sure there are two different patches we are talking about 
here. One enables primary passthrough with VBIOS POST-ing in domU, the 
other adds PCI bus reset as a means of resetting the device before 
passing it through.
Gordan

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