Mesa 22.0 Gets RADV Ray-Tracing Performance Boost By Using Wave32 Mode

Landing today for Mesa 22.0 was a fix for Vulkan ray-tracing with the RADV driver in the RDNA Wave32 shader mode and then switching to Wave32 by default for ray-tracing on RDNA/RDNA2 GPUs.

Rhys Perry's work on getting RADV ray-tracing working properly for Wave32 mode and using it over Wave64 by default has been merged. With Mesa 22.0, Wave64 is now only used for Vulkan ray-tracing shaders if the RADV_PERFTEST=rtwave64 environment variable is set.

What's important for this Wave32 RADV ray-tracing usage is the performance benefit. Perry noted with his pull request going from 48 to 54 FPS with a Radeon RX 6800 in Quake II RTX. Not too surprising considering the more efficient compute performance on RDNA(2) when using Wave32 rather than Wave64.

There still is more work to do on the RADV ray-tracing support, but work like this MR is a step in the right direction for competitive open-source Radeon driver support for Vulkan ray-tracing.