Re: [Xen-users] ATI VGA Passthrough / Xen 4.2 / Linux 3.8.10

[Gordan Bobic <gordan@xxxxxxxxxx>]

On Thu, 9 May 2013 14:20:20 +0000, Casey DeLorme <cdelorme@xxxxxxxxx> 
wrote:
> Thanks for posting the results Gordan, unfortunate that it isn't
> working as well as we hoped.
I haven't given up _quite_ yet.

I discovered yesterday that it _looks liks_ one of my PCIe slots is
actually duff (two different GPUs both fail to detect properly in it
but work fine in other slots).

If it turns out to be a duff slot, there's no telling what else
might be duff on the motherboard and how it might affect various
things, even though several days of full load stability testing
passed.

So some more bare-metal testing seems to be called for - right now I
am not prepared to disregard the possibility that maybe I have a
hardware issue somewhere that despite EDAC and ECC on everything,
remains undetected and unreported in the logs.

>   2) My motherboard's PCIe slots are behind NF200 PCIe bridges (yes,
> EVGA have decided in their infinite wisdom to put all 7 PCIe slots
> behind NF200s, none are directly attached to the Intel NB).
>
>  I'm so sorry :P. NF200 has probably caused a lot of xen tinkerers to
>  utter a few dozen cuss words a piece.
>
>  I can believe that. What is the solution, though?
>
>  The thing that drives me really nuts about the issues I'm seeing
> (which may or may not be specifically related to the NF200) is that 
> it
> is so intermittent. It works well enough to boot up and work with a
> gaming type load for a few minutes. Then something happens that 
> causes
> the VGA card to require a reset, and it all falls apart.
>
> My solution was to buy another motherboard, I had no luck at all
> passing the devices behind the NF200, and similar to your situation
> all but one PCIe slot on that board was behind that bridge.
Did you not manage to get it working at all? Or was it just
intermittent like in my case? I can typically get about 5 minutes of
gaming out of my ATI card before it all goes wrong.

Ironically, I was thinking about an Asus Sabertooth with an 8-core AMD,
but opted to go for broke and get a couple of 6-core Xeons and an
EVGA SR-2. It turns out, a solution that is 4x more expensive isn't
actually better... :(

>   What about with PCIe devices behind NF200 bridges? I know the 
> NF200s
> don't support PCI ACS, but that is a security feature (which I have
> disabled enforcement of to get this far), and AFAIK shouldn't 
> actually
> affect the basic PCI passthrough capability.
>
>  Question: how'd you disable ACS? ÂI think it may be causing me some
> issues.
>
>  Put:
>
>  (pci-passthrough-strict-check no)
>  (pci-dev-assign-strict-check no)
>
>  in /etc/xen/xend-config.sxp
>
>  If it was causing you issues, however, I'd expect you to find errors
> in logs pointing at it.
>
> As I understand the xend-config.sxp [1] is for the xm toolstack and
> deprecated Xend service.
xm toolstack and xend are what I am using. I have read reports of 
issues
with VGA passthrough using the xl stack so I didn't even attempt to use 
it.
> Perhaps I am confused, or things changed while I wasn't looking, but
> for me enabling Xend breaks the xl toolstack. ÂMy understanding is it
> was for the xm toolstack only and deprecated with 4.2. ÂAny chance
> you can share how you configured it to work? ÂApparently it is
> required to get libvirt working, which I also did not know was
> compatible with Xen 4.2.
It is possible I'm the one doing it wrong. I'm on EL6, and using
virt-manager (at least for things it is willing to do), and that
defaults to the xm stack and xend.

For what it's worth, it works for the most part - apart from VGA
passthrough crashing within 5 minutes of gaming.

Gordan

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