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

[David Sutton <kantras@xxxxxxxxx>]

Gordon,

On Wed, Mar 12, 2014 at 12:01 PM, Gordan Bobic <gordan@xxxxxxxxxx> wrote:

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.

The patch I was referring to is the same one that you are talking about; basically passing through the card as a primary display, with access to the VBIOS so the card can go through POST and be in a better internal state for when the driver starts to use 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 can concur with this - I was doing passthrough of an ATI card (6770) and it would be fine until I had to reboot that VM, at which point it would take a full restart of the host to get the card back into a fully usable state.

 

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

 

David

_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxx
http://lists.xen.org/xen-users