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Comment by w0utert | Hacker News Reader

That's pretty cool! I run one gaming VM on my 3900X but I always wondered how well it would be able to handle 2 Win10 VM's playing games concurrently. Do all the other components of the solution (both hardware and software) scale well enough for that? I assume threadripper has enough PCIe lanes and IOMMU grouping that allows for 2 passthrough GPU's + 1 for the host?

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Should handle gaming fine, you can even pin VMs on specific cores (I didn't bother). My kids play No Man's Sky with me and the 12 core 2920X handles it no issues whatsoever even though the game is atrocious optimization wise. Should have gotten a 16 core so we all three could play on same box.

X<3|4|5>70 boards should allow 2 GPUs in separate IOMMU groups. My old system was a 1700X on ASUS Prime x370 Pro with 2 gaming VMs. Only issue with x?70 boards is the IOMMU groups for USB controllers. On the Prime x370 Pro, only one USB controller is in its own IOMMU group, so second VM needed a USB passthrough.

On the Threadripper, due to the vast amount of PCIe lanes, on the Asrock Taichi x399, I got two USB controllers in their own IOMMU groups and each of the 4 PCIex16 slots it's in its own IOMMU group. It's a dream virtualization motherboard.

Is it possible to swap GPU assignments from the host OS to a guest OS and back, or does it require some motherboard-level/boot-time settings that make that difficult?

Never tried, some people had success with NVidia GPUs. However, if you are willing to put your host in sleep and wake it up, then it should be much easier. Sleep usually resets the GPU and lets host drivers grab it.

I should keep this in mind when I upgrade my workstation some time in the future. I have an x470 Taichi and there the IOMMU grouping is pretty bad, it also has only a single USB controller in its own group, and all PCIe slots except the top x16 one are grouped with other stuff so it's not even possible to plug in a separate USB controller card or a second GPU for passthrough. A ThreadRipper would have been a much better choice considering I also use this machine for development and can use all the cores I can get.

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