A little while back I took to wondering why one particular demo from the Sascha Willems vulkan demos was a lot slower on radv compared to amdgpu-pro. Like half the speed slow.
I internally titled this my "no fps left behind" project.
The deferred demo, does an offscreen rendering to 3 2048x2048 color attachments and one 2048x2048 D32S8 depth attachment. It then does a rendering using those down to as 1280x720 screen image.
Bas identifed the first cause was probably the fact we were doing clear color eliminations on the offscreen surfaces when we didn't need to. AMD GPU have a delta-color compression feature, and with certain clear values you don't need to do the clear color eliminations step. This brought me back from about 1/2 the FPS to about 3/4, however it took me quite a while to figure out where the rest of the FPS were hiding.
I took a few diversions in my testing, I pulled in some experimental patches to allow the depth buffer to be texture cache compatible, …