Bug Sur 11.4 stuttering issues on RX 6800

Bug Sur 11.4 stuttering issues on RX 6800

Partial success on OC 0.6.9, iMac 19,1. Successfully installed Big Sur 11.4, with mostly everything working (Wifi, Bluetooth, USB, Audio, multi monitor, etc), except for some graphics issues, including an annoying system stuttering.

I followed the Open Core install guide, with a few more specific pointers from here: https://www.tonymacx86.com/threads/success-asus-prime-z370-a-i9-9900k-pro-audio-build.276446/

Specs

Powercolour Red Dragon RX 6800

Intel Core i7 8700K

Asus Prime Z370-A motherboard , BIOS version 2801

Fenvi T919 Wifi

48GB Mixed RAM

1TB NVME SSD Crucial P1

Setup

Config.plist: https://pastebin.com/Pxpyx4xM

OpenCore file tree:

https://preview.redd.it/rdvjti3n4k371.png?width=451&format=png&auto=webp&s=0c2d903c40ed1168b6cf89ee1a5598e2adef4cc7

Problems

The main issue is a constant and annoying stutter every few seconds. Mostly noticeable on mouse movements, but it seems to be system wide. UFO test also picks it up:

https://preview.redd.it/xcgaclgo4k371.png?width=451&format=png&auto=webp&s=fc2602ee213f1e18b7a0b69e672891539697a8cd

Also some other graphics issues with the new GPU:

- Haven't been able to get 4k 120Hz over HDMI 2.1 working. Maxes out at 4k 60

- DRM video playback not working.

https://preview.redd.it/ryeddtel6k371.png?width=672&format=png&auto=webp&s=5b00398909b4ca4b7622a04a8bfa8f0a804ca901

Things I've tried

- Disconnecting the GPU and running with the iGPU. This runs fine without stutter, but yea, the point of installing big sur for me was to get RX 6800 support

- Windows 10 works flawlessly so doesn’t seem to be a hardware problem

- Smbios imac 19,1, imacpro1,1 and macpro 7,1, with and without whatevergreen and agpmod=pikera. Some configurations have a black screen, and some display, but all display outs have this stuttering issue

- AAPL, ig-platform-id for igpu in various combinations with enabling and disabling the igpu in BIOS. I was unsuccessful in getting igpu multi monitor working either, not sure if this is related

- Both HDMI and displayport, on multiple different monitors, at multiple resolutions/refresh rates all still stutter…

- Changing the PCIE slot of my graphics card

Anyone have a similar problem here? or can offer any pointers on other things I can try to resolve the stuttering issue?

Thanks!

submitted by /u/beetlesmuglers
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