My sincere apology for AI summary below, but after week of trying to find more about this issue i am absolutely drained.
I have also discussed this issue in this PR (which i again apologize for spam in the PR)
#3033

Software information

Game: Forza Horizon 6

Settings:

• 2560x1440
• Mostly Extreme settings
• Terrain quality set to low due to known issue for AMD GPUs
• FSR tested with almost no meaningful impact (+3-7 FPS)

Issue:
Performance is approximately 50% lower than another Linux user with nearly identical hardware and settings.

Benchmark comparison:

• My result: ~62 FPS average
• Comparison system: ~126 FPS average
• Same GPU class (RX 9070)
• Same CPU class (5700X3D)
• Same resolution/settings

Observed behavior:

• GPU usage remains at 97-99%
• GPU clocks boost correctly (~3000MHz sustained)
• VRAM clocks boost correctly (~2516MHz)
• Temperatures are normal
• No thermal throttling
• No PPT throttling
• GPU power draw remains relatively low/moderate (~110-160W average)
• FPS remains low regardless of graphics settings
• FSR has almost no impact on FPS

Additional observations:

• Diablo 4 shows somewhat similar behavior:

  • Heavy RT workload
  • High GPU usage
  • FPS drops significantly
  • Power draw remains around ~150W

• Other DX12 games fully utilize the GPU correctly:

  • Witchfire reaches ~220W
  • Half Sword reaches ~220W

This suggests:

• GPU is healthy
• Boosting behavior works correctly
• Thermals/power delivery are fine
• The issue appears workload/game specific rather than a global hardware problem

Things tested:

• Proton Experimental Bleeding Edge
• Proton GE 10-34
• Proton CachyOS
• X11
• Wayland
• Native Wayland Proton
• Fedora RPM Steam
• Mesa 26.0.9
• Mesa 26.1.0
• Mesa git 26.1.1
• Different VKD3D versions
• Shader cache deletion
• ReBAR enabled/disabled
• Kernel 7.0.9
• Kernel 7.0.10
• amdgpu.mes=0
• Different LACT performance modes
• SMT disabled
• Steam runtime tests
• Flatpak Steam tests

None of these produced meaningful improvements.

System information

• GPU: Sapphire Pulse Radeon RX 9070 16GB
• CPU: Ryzen 7 5700X3D
• RAM: 32GB DDR4-3600
• Motherboard: ASUS TUF GAMING X570-PLUS
• OS: Fedora 44 KDE
• Kernel: 7.0.10-200.fc44.x86_64
• Driver: RADV
• Mesa: 26.1.1 (also tested 26.0.9 and 26.1.0)
• Wine version: Proton Experimental Bleeding Edge / Proton GE 10-34 / Proton CachyOS
• VKD3D-Proton version: latest Proton bundled versions + Horizon fixes tested

Log files

The Proton log contains a very large amount of:

matejss@matejss:~$ tail -n 10000 steam-2483190.log | cut -c1-120 | sort | uniq -c | sort -rn | head -30 33
23224.295:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 33 23224.295:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff 33 23224.295:0140:026c:trace:seh:call_vectored_handlers calling handler at 000000014534B378 code=c000001d flags=0 30 23224.269:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff 29 23224.269:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 29 23224.269:0140:026c:trace:seh:call_vectored_handlers calling handler at 000000014534B378 code=c000001d flags=0 26 23224.315:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 26 23224.315:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff 26 23224.315:0140:026c:trace:seh:call_vectored_handlers calling handler at 000000014534B378 code=c000001d flags=0 24 23224.295:0140:026c:trace:seh:dispatch_exception code=c000001d (EXCEPTION_ILLEGAL_INSTRUCTION) flags=0 addr=000000014446 21 23224.292:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 21 23224.292:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff 21 23224.292:0140:026c:trace:seh:call_vectored_handlers calling handler at 000000014534B378 code=c000001d flags=0 21 23224.288:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 21 23224.287:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff 21 23224.286:0140:026c:trace:seh:call_vectored_handlers calling handler at 000000014534B378 code=c000001d flags=0 21 23224.274:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 21 23224.274:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff 21 23224.273:0140:026c:trace:seh:call_vectored_handlers calling handler at 000000014534B378 code=c000001d flags=0 21 23224.272:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 21 23224.272:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff 21 23224.269:0140:026c:trace:seh:dispatch_exception code=c000001d (EXCEPTION_ILLEGAL_INSTRUCTION) flags=0 addr=000000014446 20 23224.301:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 20 23224.301:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff 20 23224.301:0140:026c:trace:seh:call_vectored_handlers calling handler at 000000014534B378 code=c000001d flags=0 20 23224.300:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 20 23224.300:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff 20 23224.300:0140:026c:trace:seh:call_vectored_handlers calling handler at 000000014534B378 code=c000001d flags=0 20 23224.289:0140:026c:warn:seh:dispatch_exception backtrace: --- Exception 0xc000001d. 20 23224.289:0140:026c:trace:seh:call_vectored_handlers handler at 000000014534B378 returned ffffffff

matejss@matejss:~$ grep -c 'ILLEGAL_INSTRUCTION' steam-2483190.log
3520701 `

Disabling logging with WINEDEBUG=-all does not improve performance.

Additional technical information:

• PCIe link verified as Gen4 x16
• GPU boosts correctly to ~3000MHz during benchmark
• VRAM boosts correctly
• GPU usage remains ~99%
• No thermal throttling observed
• No PPT throttling observed

This does NOT appear to be:

• thermal throttling
• PCIe lane issue
• CPU bottleneck
• RAM issue
• shader cache corruption
• compositor issue
• low clocks / boost issue

The GPU boosts correctly but performance remains abnormally low in some DX12/VKD3D workloads.