[account42]

AMD had developers working on radeon (the older open source kernel driver) and radeonsi (the open source user-space OpenGL driver backend for newer cards in Mesa that now sits on top of amdgpu) before the switch to amdgpu (the newer open source kernel driver). While the kernel driver isn't irrelevant for performance, it depends more on the user space portion (radeonsi and r600 before that) which was kept with the amdgpu switch. What the amdgpu driver brought is more sharing of display code with their windows drivers. The main difference in performance is between r600 (mostly developed without financial support from AMD) and radeonsi (mostly developed by AMD). Of course these days the most relevant user-space portion is radv (open source Vulkan driver in Mesa) which is NOT developed by AMD but rather funded by Valve (and at least initially Red Hat). There is also the open source amdvlk Vulkan user-space driver developed by AMD which is the same as their proprietary Vulkan driver except with the proprietary shader compiler swapped out for the same LLVM backend that radeonsi uses. And if this all wasn't confusing enough, AMD also calls the full driver package with the proprietary Vulkan driver and some snapshot of the open source OpenGL Mesa drivers (radeonsi) "amdgpu-pro".