I’m in the same boat, I have been trying to get Multi GPU running in Unreal since UE4 and it still not looking great in UE5. From my research there is a couple of commands targeting DirectX 12 mgpu but the engine just crashes when used in conjunct with ray-tracing or Lumen. The commands I found must be run on the .uproject which are:
“-game -d3d12 -MaxGPUCount=2 (or number of GPUs in your system up to 4) -AFR”
and if you want to test a multi GPU setup with a single GPU system you can add -VMGPU. I also found these console commands that you can add to your ini config file:
r.AllowMultiGPUInEditor 1
r.EnableMultiGPUForkAndJoin 1
r.PathTracing.GPUCount 2
D3D12.AFRSyncTemporalResources 1
D3D12.AFRUseFramePacing 1
r.GPUParticle.AFRReinject 1
An example if you want to try it on your system is to run this in CMD (Command Prompt):
“C:\Program Files\Epic Games\UE_5.0EA\Engine\Binaries\Win64\UnrealEditor.exe” “C:\Users\Public\Documents\Unreal Projects\UE5Test\UE5Test.uproject” -game -d3d12 -MaxGPUCount=4 -VMGPU -AFR
change the second path to your project file.
Also go to your project config folder “C:\Users\Public\Documents\Unreal Projects\UE5Test\Config” then edit DefaultEngine.ini if there is no [/Script/Engine.RendererSettings] section add it and the add:
r.AllowMultiGPUInEditor=1
r.EnableMultiGPUForkAndJoin=1
r.PathTracing.GPUCount 4
D3D12.AFRSyncTemporalResources=1
D3D12.AFRUseFramePacing=1
r.GPUParticle.AFRReinject=1
then try re-running the game in CMD again with the command above.
Your game might sometime boot up, flicker and then crash. If you do find out any other changes to make mgpu work please do share!