RadeonSI Enables DCC Stores For RDNA2 APUs To Squeeze Out More Performance

RadeonSI Gallium3D as the official AMD OpenGL Linux driver has mirrored the unofficial RADV Vulkan driver in enabling DCC stores support for RDNA2 APUs in the name of greater performance.

This merge is the latest optimization to RadeonSI by well known AMD developer Marek Olšák. This follows the same approach as RADV around delta color compression stores to allow for better performance on RDNA2 APUs.

But with no RDNA2 APUs officially released yet, there are no performance figures yet to report how much this change benefits RadeonSI. With the prior RADV work on enabling DCC stores, one of the enablement patches there from one of Valve's driver developers noted that it provides a "2~3% improvement most of the time."

The changes do add new debug options of "nodccstore" and "dccstore" for manipulating the DCC stores usage. The default enabling is just for GFX10.3/RDNA2 APUs and newer. One of the code comments does note, "DCC stores have 50% performance of uncompressed stores and sometimes even less than that. It's risky to enable on dGPUs."

Great seeing the Mesa Radeon OpenGL/Vulkan components continue to get ready for RDNA2 APUs.