Arch Linux

n00d13

Member

Registered: 2022-06-12

Posts: 6

Single GPU passthrough vs dual GPU passthrough

so ill keep it short, im planning to build a new rig with an rx 570 with either an i3-10105f or an i3-10100 (difference is about 0.1-0.2 ghz clock speed) for about the same price for me

is there any performance differences between single vs dual gpu passthrough in gaming under a windows vm? what's the practical difference too? or should i just buy the slightly higher clock speed cpu instead of the one with an igpu?

i hope this is the right tag to ask this question, thanks

Lone_Wolf

Member

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 11,911

Re: Single GPU passthrough vs dual GPU passthrough

Assuming you want to passthrough the rx 570 to the VM, there shouldn't be any difference in performance for the VM.

Stability (both host & guest) is likely better with  a dual gpu setup, but a single gpu setup may be easier to configure .

The main drawback I see for a single gpu setup is that you will loose majority of host functionality while using the VM.

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ravensiris

Member

Registered: 2022-06-15

Posts: 1

Re: Single GPU passthrough vs dual GPU passthrough

I've been running a single GPU passthrough setup with a RX580, 3900X and 32GB of RAM for 2 years now.
And I also built a 2 GPU setup for my brother with a RTX 2080S and an old hd 5570, 2700X and 16GB or RAM.

Issues you might encounter when using 2 GPUs:
You would be running two systems with GUI environment at once, this in turn requires more RAM allocated to the host as well as more CPU cores/threads.
You might want to have 32GB+ RAM depending on your use case. In my brother's case 16GB is often not enough when gaming and running VS Code + Firefox on the host.
You also might need a processor with more than 8c2t (8 cores, 2 threads each), again depending on your use case. 2700X is not good enough for VS Code + Firefox + Gaming.

Issues you might encounter when using 2 GPUs:

Dreadful reset bug in RX 5xx series AMD GPUs. Basically you won't be able to switch between HOST<->VM without restarting without using some tweaks. I had to completely disable my host from using my gpu by not compiling my kernel with support for my RX580 and adding: "pcie_acs_override=downsteam,multifunction acpi_enforce_resources=lax video=efifb:off" to GRUB_CMDLINE_LINUX in "/etc/default/grub". This sucks, since only way of accessing the host is ssh or removing the options by pressing 'e' key in the GRUB screen.

It feels like a glorified dualboot. There are some advantages(like having a Windows VM isolated through NAT and on a encrypted LVM partition) but you don't feel as much of the cool factor as using 2 GPUs.

I'd say build your PC in a way you can eventually get a second GPU. And save yourself a headache and don't buy AMD GPUs with the reset bug(hopefully 5000 series don't have this problem)
I've done that right before the prices soared to the moon and didn't get to buy a second GPU yet. Will do that when the prices are below MSRP(hopefully soon).