GPU Passthrough

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GPU Passthrough

Christoph Kaminski

Hi

I think about create a windows HVM domU with gpu passthrough on xen to
stream via steam games to my linux workstation.
I have some question about this setup:

1. Have someone tried it? Does it work as expected?
2. What is easier and what is most stable: primary or secondary gpu
passthrough? (I have a ATI Radeon HD 6950 GPU now but I want to buy a
nvidia in the near future)
3. Which settings gives the windows domU the needed priority? (I have
some PV linux domU's on this hypervisor, they should work simultaneously
but the most ressources should get the windows domU becaues of play a
game)
4. What would be the virtualization loss vs bare metal windows?
(approximately)

My setup:
CPU: Intel(R) Xeon(R) CPU E3-1271 v3 @ 3.60GHz
RAM: 32GB
GPU1: GeForce 6200 LE
GPU2: ATI Radeon HD 6950

Win DomU:
CPU: access to all CPU's
RAM: 16GB
GPU Passthrough: ATI Radeon
HD: dedicated SSD

THX in advance for your answers...

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Fwd: GPU Passthrough

Stephen Oberholtzer
(apparently I accidentally chose 'reply' instead of 'reply all', resending to whole list)


On Sat, Jun 30, 2018 at 5:40 AM, Christoph <[hidden email]> wrote:

Hi

I think about create a windows HVM domU with gpu passthrough on xen to stream via steam games to my linux workstation.
I have some question about this setup:

1. Have someone tried it? Does it work as expected?
2. What is easier and what is most stable: primary or secondary gpu passthrough? (I have a ATI Radeon HD 6950 GPU now but I want to buy a nvidia in the near future)
3. Which settings gives the windows domU the needed priority? (I have some PV linux domU's on this hypervisor, they should work simultaneously but the most ressources should get the windows domU becaues of play a game)
4. What would be the virtualization loss vs bare metal windows? (approximately)

 
(1) I have a Windows HVM that I'm doing GPU passthrough, it's running Windows 10 (originally Windows 8).  I use it to play games (mostly from Steam).
I'm running on Xen 4.9, Dom0 is Debian 9.0 "Stretch".

Here are a few things to note:

* Obviously, your CPU needs to have an IOMMU. For Intels, that's VT-d support.  I think that your Xeon will qualify (I have a Core i7, specifically a i7-4790S)

* Less well known is this: Your motherboard, and particularly your BIOS, need to have some mojo going on to make GPU passthrough work.  I don't know why.
    ASRock motherboards seem to have good IOMMU support; my setup is on an ASRock  H97M Pro4.

* Don't go with nVidia; their drivers are specifically designed to *not* work with GPU passthrough unless you have a (very expensive) Quattro card.

* ATI/AMD cards, on the other hand, don't support something called FLR, which means (2) they're unsuitable for being passed in as the primary GPU.
    My Windows DomU has the cirrus VGA passed-through as the primary GPU; Windows is configured to ignore that GPU and use only the the AMD card for the display.

   A side effect of this is that some Windows updates, as well as AMD driver updates, end up switching back to the virtual cirrus card; when that happens I need to use VNC to get in and repair it.
   So you'll need to make sure you enable VNC on your VM in case you need to rescue it.

* I have the motherboard's USB passed-through to the DomU as well (all actual administration of the host is done via SSH).
     I had to add a flag to allow insecure pass-throughs (I think it's "permissive=1") because the other peripherals on the motherboard had shared MTRRs or something.
     I had tried to put in a PCI USB card, but I tried three different cards and none of them worked correctly when passed-through, so I gave up on that.

Those are the main things I remember encountering with regard to setting it up and keeping it running.

(3) The other VMs aren't very heavy load (they're just some internal websites used to trigger Smart Home stuff), so I've never had to deal with prioritization.

(4) I don't know what the performance loss is, but I do know that the system can handle itself pretty well.  Games that depend heavily upon the GPU -- DOOM 2016, Wolfenstein: The New Order, etc -- run great under my R250.   Games that are very highly CPU-bound, like some Unity engine games (Dreamfall Chapters comes to mind) don't do as well; however, that might just be because my CPU, an i7-4790S, is a low-TDP version with a lower-than-average clock speed to keep the temperature down; for all I know, Dreamfall Chapters would have run poorly even without the VM interception. 

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Real programmers use COPY CON PROGRAM.EXE




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-- Stevie-O
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