Mesa 21.1 RADV Adds Another Performance Knob For RDNA2 Testing

For those that managed to get their hands on Radeon RX 6000 series hardware and are habitual Mesa Git users, the newest Mesa 21.1-devel code for RADV has a new knob for performance testing.

The newest RADV feature to land for Mesa 21.1 is delta color compression (DCC) support for storage images. This functionality was already in place for GFX10 (see this 2019 article when the Navi DCC for storage images code was first added) while now has been extended to cover GFX10.3 (Navi 2x) graphics processors too.

Given the current lack of testing, this performance feature is currently hidden behind the environment variable RADV_PERFTEST=dccstores. Set that if wanting to test out DCC for storage images with Radeon RX 6000 series graphics cards on Mesa Git. Hopefully the patch will be enabled by default in short order assuming the testing pans out and the performance gains are there -- similar to the original support for Navi 1x first having been hidden behind a similar feature flag.

This support is contingent upon using the (default) RADV ACO back-end and not the AMDGPU LLVM back-end. Additionally, like with GFX10, the DCC is only enabled if using two MSAA samples or less. Greater than two samples for the multi-sample anti-aliasing is causing conformance test suite failures for reasons yet to be determined.

Since earlier this year AMD has offered similar functionality within their RadeonSI Gallium3D OpenGL driver.

Fresh Radeon RX 6000 series open-source benchmarks are coming up on Phoronix shortly with the Mesa 21.1 feature freeze quickly approaching.