ATI Radeon KMS vs. UMS Performance With Ubuntu 10.04
Starting with World of Padman, the UMS code-paths were significantly faster than with KMS. At 800 x 600, the RV770 GPU ran at 76 FPS with the default KMS experience but that averaged out to 95 FPS when user-space mode-setting was used. When the resolution was increased to 1920 x 1080 with this ioquake3 game, the KMS average was just under 50 FPS while using UMS the average number was at 72 FPS.
The situation is the same with OpenArena, but at 1920 x 1080, the delta between UMS and KMS was smaller. At 800 x 600, however, OpenArena had an average frame-rate of 80 FPS but it was nearly twice as high with UMS at 156 FPS.
Tremulous really struggles with the current open-source ATI driver stack where even with this high-end ATI RV770 graphics processor the frame-rates were always below 30 FPS even with the older UMS implementation.