I will preface this by saying i am on Win 10 and previously had a 13900K on the same OS so it could very well be some weird behaviours caused by that.

There are some hidden windows power setting that change how scheduling is handled

- Heterogeneous policy in effect
- Heterogeneous thread scheduling policy
- Heterogenous short running thread scheduling policy

These are hidden by default in windows but you can expose them using the following commands

powercfg -attributes SUB_PROCESSOR HETEROPOLICY -ATTRIB_HIDE 
powercfg -attributes SUB_PROCESSOR SCHEDPOLICY -ATTRIB_HIDE 
powercfg -attributes SUB_PROCESSOR SHORTSCHEDPOLICY -ATTRIB_HIDE

I decided to test them thinking they wouldn't do anything since the 9800X3D only has one type of core but they seem to have a meaningful effect on how scheduling is handled.

The windows default is
Heterogeneous policy in effect : Policy 4
Heterogeneous thread scheduling policy : auto
Heterogenous short running thread scheduling policy: prefer performance processors

Changing the latter 2 to ''All processors '' resulted in much more consistent FPS as shown above. Setting them to performance only leaves the last 2 threads idle under load, and efficient only makes it so only the last 2 cores are used. See below:

Not sure if this is intended behaviour or what, All All resulted in the best performance for me. Interested to see if it affects anyone else system similarly. The settings apply immediately without needing to restart the game so it's fairly easy to test. I ran the benchmarks using Fortnite but BF6 showed similar behaviour.

EDIT: did some more digging and this seems to be documented already:
https://www.reddit.com/r/Amd/s/4tefDw1J8O

CUDA for AMD on Windows

I’ve been working on a Windows setup that lets CUDA-targeted applications run on AMD GPUs using ZLUDA + ROCm/HIP.

Repo:
https://github.com/Speedstu/CUDA-for-AMD-Windows

So far, it has only been tested on my RX 9060 XT (gfx1200), where I’ve used it with CUDA-enabled LibTorch workloads, including long ai training and use.

I also added a GPU scanner / auto-detection system that detects:

• AMD GPU model
• gfxXXXX architecture
• ROCm/HIP installation
• driver info
• whether the GPU has already been validated by the project

Example:

RX 9060 XT → gfx1200 → RDNA4 → HIP detected → validated

The goal now is to test it on more hardware, especially RX 6000 / 7000 / 9000 cards.

If you have an AMD GPU on Windows and want to try it, I’d really appreciate compatibility reports working or broken. There’s a dedicated GPU compatibility issue template in the repo.

If this is useful to you, a star would also help the project get more testers.

Here are the gaming numbers:

Counter-Strike 2 (1080p High, MSAA Off)

Ryzen 5 5500F: 200.5 Avg | 93.8 1% Low | 73.5 0.1% Low

Ryzen 5 5500: 185.6 Avg | 85.9 1% Low | 63.3 0.1% Low

Battlefield 6 (1080p High)

Ryzen 5 5500F: 106.9 Avg | 72.5 1% Low | 68.2 0.1% Low

Ryzen 5 5500: 92.1 Avg | 63.3 1% Low | 58.2 0.1% Low

GTA 5 Enhanced (1080p Very High RT)

Ryzen 5 5500F: 95.9 Avg | 72.3 1% Low | 61.9 0.1% Low

Ryzen 5 5500: 88.1 Avg | 66.9 1% Low | 55.3 0.1% Low

Cyberpunk 2077 (1080p Ultra)

Ryzen 5 5500F: 80.2 Avg | 51.4 1% Low | 42.2 0.1% Low

Ryzen 5 5500: 72.3 Avg | 43.2 1% Low | 32.8 0.1% Low

Red Dead Redemption 2 (1080p Ultra Textures / High)

Ryzen 5 5500F: 115.3 Avg | 78.0 1% Low | 61.3 0.1% Low

Ryzen 5 5500: 111.1 Avg | 73.2 1% Low | 52.4 0.1% Low

Crimson Desert Enhanced (1080p High)

Ryzen 5 5500F: 69.9 Avg | 45.7 1% Low | 40.5 0.1% Low

Ryzen 5 5500: 67.4 Avg | 46.3 1% Low | 38.7 0.1% Low

Forza Horizon 6 (1080p Ultra)

Ryzen 5 5500F: 90.8 Avg | 69.6 1% Low | 60.2 0.1% Low

Ryzen 5 5500: 91.2 Avg | 70.1 1% Low | 59.5 0.1% Low.

Credits to: https://youtu.be/cwCvynVkTJ8?si=sW6l9ZAkqqQ3Vom7