AMD GPU passthrough

Hey all,
I am in the process of building my PC and I would like to attempt single gpu passthrough for the main reason of gaming on windows while having linux installed natively on my machine , however I am trying to research the current way to do and also I have some questions that i haven’t been able to find online. First off I am running a 5800x AMD cpu and a single 6800xt gpu I don’t know what motherboard to buy because I don’t know which one would support virtualization the best given these components, I have been considering at least the b550 but I don’t know if I need a x570. my next question I am going to run Manjaro linux (arch ) just because I am more comfortable with it and it is very lightweight, what would be better for virtualization running KVM or virtual box . Finally I am worried that gaming on a virtual machine and seeing if it is even worth as far as performance, in the end is it worth the headache or should I just run windows natively?
thanks all

Hello Hello,

You got a lot of questions there, but it boils down to use-case.

Are you daily driving the windows VM? Or are you only going to start it just to play games? What is the point of the base linux install?

As for motherboards if you are only passing 1 graphics card through (the main gpu) Then a b550 would be fine. However, if you had 2 gpu’s say, 6800xt and a 5700. Some motherboards bifurcate the pci-e slots, so both would run at 8x, and sometimes the Second pci-e 16 slot will only be a pci-e [email protected], or even worse [email protected] speed. So, if you were going to do 2 graphics card, I would personally go with the x570.

X570’s also sometimes will have dual nics, dual nvme slots, proper pci-e 16x 4.0 slots - I was gonna grab one, but… decided to hold off for now.

Always always always, the easiest is have 2 gpu’s. 1 for the host system 1 for the gpu passthrough to the vm. Do you need the 6800xt on the linux host for work? Or is is JUST for gaming? You can passthrough the main GPU but it is more complicated, and some people run into major problems.

KVM vs virtual box. Ummm maybe you can use virtual box, I’ll be honest never tried it, maybe someone else can chime in. But I love KVM, it has always worked great for me.

You do loose performance in the windows VM, specifically ram performance, storage performance, and unless you are pinning you CPU, you can get some stutters / performance issues. With the basic vm setup. Thing can be improved with passing through an entire controller for a nvme drive, enabling huge pages for ram performance, Cpu Pinning etc.

However I would expect about 5-10% Performance loss.

So it worth it? It really depends, depends what you need to do, what the use case is. So it’s completely up to you, I think when I first got my VM working, it was the coolest thing I’ve ever experienced.

Also I know Wendell, has been known to say. “Who would ever run windows on baremetal” Simply because of the anti-privacy junk inside windows, the constant phoning home etc.

Hey RustyP, I know that you are wanting to do a gpu passthough with manjaro but have you considered using something like unraid or truenas to run your vms. If it’s your first time passing though a graphics card I would recommend using one of these as you will probably have an easier time getting it up and running. Something to think about because you can always get something running on manjaro later, but at the end of the day you probably want something that will work and there are tones of videos and forum posts out there for getting passthought to work at least for unraid which is what I use. It would also be very easy to play around with creating a nas or using docker as a added plus. Something to think about.

Hello,

Yesterday i moved away from a gaming VM, I found some games will not work (due to anti-cheat) or threaten bans for using a gaming VM. You can get around this, but for me the time investment to cover up using a VM was just to great. Also lots of the games I play I really do not want to risk getting my account banned. It can be nice to dual boot just to separate work and play.

Just look around at what other people are running for motherboards. Asus TUF X570-Plus is what I used and had zero issues, but your millage may vary.

Single GPU can have issues. Definitely do your research on it, i have not tried it. I am pretty sure that you have to control the host over the network from the guest. From what I have seen it gets to be annoying.

A PCI USB card and an extra nvme slot is nice to have as well. just pass though the entire usb card and disk. It makes things less complicated in my experience. Things like gamepads and racing wheel are easier, without having to lose usb ports on the host.

KVM all the way, arch wiki has a good guild on GPU passthough.
Wiki link

You will lose performance. It seems to be pretty game depended on the FPS drop. It felt like some games were near perfect and I could hardly notice a difference. Other i could definitely feel a difference.

If it is worth it is entirely up to you. It was for me I enjoyed playing with it and had fun setting it up. I learned a lot form it and may go back it.

Yeah… Truenas and unraid are much less flexible when it comes to passthrough. They operate on the “it always works” philosophy and that’s absolutely not the case.

In fact, it’s easier to just do it manually because then you know what to fix when it inevitably breaks.

Ya it is true that it can be more flexible and easier to do manually if you are more comfortable with doing it that way; however, I think it kinda depends on what you are most comfortable with and at what knowledge level you are starting from. It can be easy to get frustrated and or overwhelmed or completely lost when starting from scratch. I don’t mean to imply that it will always work no mater what you do or that unraid or truenas is the best solution for you, but it’s at least something to look at and consider.

Basically I want Linux as a host because it’s not windows, however I want to create these vms because I think it will make my machine more versatile, for example I don’t want everything running on my host machine, another goal of my machine is too run emulators and In the past I’ve ran emulators on a Linux machine with lutris it worked great however my machine crashed and I don’t know if it was a bad rom that gave me a virus or the machine gave out( this machine has giving me problems, that’s why I put Linux on it )

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