Mesa Radeon Vulkan Driver "RADV" Works Around Bugs For Unreal Engine 4 & 5

[phoronix]

Phoronix: Mesa Radeon Vulkan Driver "RADV" Works Around Bugs For Unreal Engine 4 & 5

Thanks to prolific Mesa RADV contributor Samuel Pitoiset of Valve's Linux graphics team, a fix is on the way for addressing various issues with Unreal Engine 4 and Unreal Engine 5 games running on Linux via Steam Play...

https://www.phoronix.com/news/RADV-Mesa-UE4-UE5

[ernstp]

If I understand correctly, this is for Linux _native_ Unreal engine programs. DXVK already zeroes out the vram for everything so you don't see the issues there.

[aufkrawall]

If I understand correctly, this is for Linux _native_ Unreal engine programs. DXVK already zeroes out the vram for everything so you don't see the issues there.

VKD3D-Proton (UE5 basically is D3D12-only) doesn't zero by default and needs RADV to do it in such cases.
Good thing is this also helps against stutter introduced by some amdgpu kernel driver changes.

The Talos Principle 2 already runs 10% faster for me than on Windows, wouldn't have expected AMD to throw away that much performance even with UE5 and their native D3D12 driver.

[Kjell]

Are there any disadvantages to using RADV_DEBUG=zerovram all the time?

[aufkrawall]

Are there any disadvantages to using RADV_DEBUG=zerovram all the time?

This causes visual corruption in Ratchet & Clank. Though in most cases (afaict), it seems to be fine.

[Kjell]

This causes visual corruption in Ratchet & Clank. Though in most cases (afaict), it seems to be fine.

Other than the risk of visual glitches, does it improve performance to have it on all the time or is UE4/UE5 a edge case?

[peppercats]

Other than the risk of visual glitches, does it improve performance to have it on all the time or is UE4/UE5 a edge case?

Performance would be improved by not having it on.

As an aside, last I checked nvidia's drivers clear by default and have an option to turn it off. I don't recommend it.

[Serafean]

Other than the risk of visual glitches, does it improve performance to have it on all the time or is UE4/UE5 a edge case?

It shouldn't be able to improve performance. Allocation is a simple operation, a few pointers changed, a few counters updated. Zeroing the allocated area requires writeback to physical memory of the whole range. (barring special optimizations for zeroing out, which do exist, so at best it can be only as expensive as allocation)

[aufkrawall]

Oops, I think I've spread misinformation and confused RADV_DEBUG=zerovram with radv_zero_vram=false . Need to read up a bit, sorry...

[Cryio]

I basically use RADV_ZERO_VRAM=false with literally any game. It either does nothing or it improves framepacing.

It also seems to impact DX12 titles (not UE4/5 DX12 necessarily) way more than DX11 titles.