Thanks a lot @Matrix, that’s exactly the data I was missing. Knowing the modded BIOS also loses performance on CachyOS is a strong sign that the problem is in the patched firmware and not in Windows or the driver.
I’d like your opinion on one thing. @Guava just got ReBAR enabled on a GA-Z97X-Gaming 7 with a 4790K and the same GPU I have (RX 9060 XT 16GB): [Offer/Guide] Optimized GA-Z97X-Gaming 7 BIOS
His setup is different from yours in a few ways:
- Only a 1GB BAR (2/8/16GB hung at POST)
- A custom DSDT window instead of the PciHostBridge 512GB MMIO + NBPEI 39-bit patches (his old patches.txt didn’t have them)
- He reports the system is stable and games load faster, but he has not posted fps numbers yet
Do you think the performance loss you saw could come from those two patches (512GB MMIO / 39-bit address space, BAR placed at a very high address) rather than from ReBarDxe itself? Did you ever try a smaller BAR (1GB or 2GB), or a build without those two patches, to see if the fps drop was still there?
And about the native Linux route:
1. On CachyOS with the stock BIOS, did you measure a real gain with ReBAR on vs off (Above 4G Decoding enabled vs disabled)? Any average / 1% low numbers?
2. What BAR size does the kernel assign to your RX 6700 XT? The full VRAM?
3. Was Above 4G Decoding really the only change, or did you need a kernel parameter like pci=realloc?
I’ll hold off on flashing until this is clearer. Thanks again for testing all this.