QEMU/KVM GPU pass-through recommendations

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

Hello,

I have a Windows 10 VM that I use for Photoshop and sometimes some light gaming on Steam. The performance is quite laggy, even in Photoshop, so I would like to get a GPU to pass-through to the VM via QEMU/KVM (using virt-manager). I have a free PCIe 4.0 x16 slot available, and would like to find a decent AMD-based GPU for a reasonable price to handle these relatively light tasks. Do you have any recommendation on models that would be good for this purpose?

Thank you in advance.

Cheers,
Nathan Zachary
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DaggyStyle · Watchman Joined: 22 Mar 2006 Posts: 5915

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

That would require going headless on my main workstation then, I guess. That could be an option if need be. I also could try to spend more time optimising the VM because it seems odd to me that even moving a window around the screen has lag. Maybe there are better settings for performance?
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szatox · Advocate Joined: 27 Aug 2013 Posts: 3228

Moving windows is laggy?
Are you sure you have kvm enabled?
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NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

Yes, there is a noticeable delay when performing basically any task in the Windows 10 VM. Here are some details:

Anon-E-moose · Posted: Fri Jul 05, 2024 5:51 pm Post subject:

Hard to say what's up, without seeing the config file.

But with win10 and up, you could use virtio-gpu, instead of a passthrough gpu.
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mrbassie · l33t Joined: 31 May 2013 Posts: 804 Location: over here

Ralphred · Guru Joined: 31 Dec 2013 Posts: 539

I uploaded this 5 second clip of the lag I get when using QXL on my windows VM. This lag is gone when using passthrough to an old RX560 card (Baffin - polaris11).

There are two other things that have seriously improved the performance:

Giving the VM its own SSD to run from*, the xml for it is below

Code:

This obviously doesn't effect input or display lag, but it's much snappier to work with.

Using https://atlasos.net to cut back on windows footprint and overhead. I only use(d) passthrough to run one game, a Ubisoft title, so a pretty good test of functionality, it worked flawlessly.
It's fair to say that running Atlas in a VM >= Running vanilla windows 10 on the same hardware with no hypervisor - from a UI usability point of view. If it works for you in testing, I can't recommend it enough.

*I run two VM "templates" in VMM using the same partitions of the physical disk - one the "original" VM before making the changes to allow GPU passthrough, then the passthrough enabled VM. As long as I don't try and boot them both at the same time it works fine (as in I'll get QXL video if running one, passthrough the other). I think if I were to sysprep the windows install it might be bootable in a non-vm environment, it certainly has "all the right bits set" when viewed in parted.

LiamOS · n00b Joined: 06 Jun 2012 Posts: 65 Location: Ireland

I picked up an AMD 6500XT second hand recently for this exact purpose, was pretty much plug-and-play.
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Cruslan · n00b Joined: 06 Jan 2024 Posts: 20

You can use 60 FPS patch for QEMU. In default QEMU's frame intervals set to 30 ms(about 30-31 FPS). It can be quite laggy. By decreasing that to 16 ms(60 FPS~) you can get better display output. You can apply that patch to app-emulation/qemu package. Patch;