Why is DX12 so much slower than DX11?

[dnach]

@Bwacky

After ages, I gave DX12 another try today across a few editor versions, all in URP, all running on Unity 2022 since I’m not interested in U6 for now.

FPS is essentially halved in every single test scenario, with some test scenes I ran having only a 30% drop (yippee).

An average of 50% FPS drop in real scenes you’d usually work with (open world RPG type scenario with NPCs, some physics, water, sky, vegetation).

Not a single setting helps to improve this. Is there any reason to use DX12 other than HDRP’s ray tracing support which doesn’t even exist in URP? I’m on a 3080 with a 7950x3d here and the whole reason to even use it was improved performance in real-game scenarios and CPU alleviation via split graphics jobs from my understanding, yet the performance is quite literally halved.

The worst case I had was a 16-22 fps average in a scene running DX12 vs 55-60 in that same scene running DX11. I am testing the editor because nobody is going to suffer through this much pain developing on DX12 to then see if maybe a build is faster or the same. I don’t think I’ve met a single real person on any developer discord or sub-forum saying DX12 is usable. Not even one person.

Are there any published sample demos from Unity where we can swap from DX11 to DX12 and observe those incredible gains ourselves? I mean an accessible demo, not a YouTube video or a fancy graph PNG with a big bar above dx12 and a small bar above dx11.

Hey! As it relates to Unity 2022, we usually recommend DX11. Hence it is set as “default”, meaning the first priority in the Auto Graphics API settings. Unity 6 introduces meaningful improvements to DX12 so I recommend giving it a try and sharing what you see.

There are good reasons to use DX12 besides Ray Tracing. Multithreading is a good example. Based on our tests, using internal benchmarks and actual game projects, Split Jobs (Unity 6) seem to be effective at reducing CPU latency, Both in the Editor and Player. There are other benefits, like async compute, Native Render Pass support (for ARM based devices) and PSO tracing to eliminate stutters.

If you see such a drastic regression in performance compared to DX11 also in Unity 6, please share more details! For the last question, a quick way to test would be to fetch the 3D sample projects from the Unity Hub (Create new project → Sample).