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

["H. Sieger" <powerhouse.linux@xxxxxxxxx>]

I can't (and won't) argue with trying it out. However, the issue here (performance loss/instability after domU shutdown/reboot) has nothing to do with blacklisting the graphics driver. Blacklisting the graphics driver(s) is not only necessary for AMD/ATI graphics cards, but also for Nvidia cards. This has to do with how and when pciback (or pci-stub) is trying to grab the graphics card - if that happens after a graphics driver took possession, bad luck (according to my experience).

Now that you mention pci-stub, have you tried pciback? Perhaps the whole issue is pci-stub related?

On Wednesday, March 12, 2014 10:49 PM, Gordan Bobic <gordan@xxxxxxxxxx> wrote:

On 03/12/2014 08:12 PM, H. Sieger wrote:
> Now you really made me curious. I have two ATI cards (a Sapphire Radeon
> 7770 and a Sapphire Radeon 6450) in two different PCs and could use them
> for a test in my rig, running it from a Xen installation on an external
> USB drive so I won't have to compromise my regular system. Just need to
> find the time.
>
> Your experience is also in contradiction with the Xen wiki:
> http://wiki.xen.org/wiki/Xen_VGA_Passthrough_Tested_Adapters.

Not contradictory, my definition of "working" just happens to be more
stringent.

> I have collected user reports of successful VGA passthrough - see here:
> http://www.overclock.net/t/1307834/xen-vga-passthrough-compatible-graphics-adapters.
> There aren't too many posts there, some do mention guest reboot issues,
> but it seems there are few. Each card that's been listed should have a
> link to a user report.

I suggest you just try it. I don't think there's a single person on this
list that will tell you that ATI cards work just fine across domU
reboots. This is also why it is imperative you blacklist your radeon and
fglrx modules in dom0. If you don't, the driver will initialize the card
before it is taken over by the pci-stub driver, and you'll have the same
problem on the initial domU boot.

Gordan

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