RADV driver fix delivers an incredible performance boost on RDNA 2 hardware using FSR 2, reducing the performance gap that existed for two years.
Valve engineer fixes problems with the RADV driver by reworking just ten lines of code to deliver a 228% boost in performance in FSR2 titles
The Mesa 24.3 has finally fixed the major issue with the RADV(Radeon Vulkan) driver, which led to inferior performance compared to AMD's proprietary AMDVLK/AMDGPU-PRO Vulkan driver. This performance gap existed for nearly 2 years when the FSR 2 was turned on in games. It has been successfully fixed by Valve's Linux driver team by just tweaking a few lines of code.
The credit goes to the engineer, Samuel Pitoiset, who, as reported by Phoronix, identified the issue and fixed the problem by tweaking less than a dozen lines of code. For context, the RADV driver is an open-source Vulkan driver for AMD GPUs for the Linux OS. Being open-source and open to the community has led to its increased popularity among users, but the problem used to occur when FSR 2(FidelityFX Super Resolution 2) was turned on.
The performance was poor compared to the AMDGPU-Pro driver, which is optimized by AMD itself. Nearly 2 years passed, but there was no fix until Samuel identified the root cause of the issue. This was specifically due to how the RADV driver handled the culling of primitives with specific characteristics in FSR 2. In simple words, culling is how unnecessary primitives like triangles and lines are discarded before rendering to improve performance by saving power.
It looks like the fixed-func hardware is very slow to cull primitives with zero pos.w but shader based culling helps a lot.
This fixes a massive performance gap with the FSR2 demo compared to AMDGPU-PRO, +228% on RDNA2.
-Samuel Pitoiset (Credit: Phoronix)
With the AMDGPU-Pro driver, this is handled easily as the driver culls primitives with zero in the "W" position. RADV, on the other hand, wouldn't do the same, which resulted in additional and unnecessary calculations that slowed down the performance of FSR 2 applications.
As indicated by Samuel, making adjustments to the AMD NIR code enforces culling when the W position is zero. This helped the RADV driver achieve an incredible 228% performance boost on RDNA 2 GPUs when the FSR 2 is turned on. This improvement will be available to the users through the official release and is a part of Mesa 24.3-devel.
News Source: Phoronix
About the author: Sarfraz Khan is a hardware reporter with a focus on PC components and the builder community. With years of experience writing about PC hardware and laptops, his work has been featured on several reputable technology publications. Sarfraz's hands-on experience is demonstrated through his first-person accounts of using and comparing different hardware configurations, providing practical and relatable insights for everyday users. His technical analysis is respected by peers in the enthusiast community and has been cited by specialized hardware sites such as Germany's Igor's Lab.
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