Radeon vs. Modesetting DDX Driver Performance On Ubuntu 16.04
Following the quick DRI2 vs. DRI3 rendering tests with Radeon on R600g, I also did tests on the same system of the xf86-video-ati vs. xf86-video-modesetting DDX drivers.
Just for curiosity sake, I wanted to see the impact of switching out the default xf86-video-ati X.Org driver on Ubuntu 16.04 LTS for the generic xf86-video-modesetting DDX driver that's been part of the X.Org Server. In this round of tests was just looking at the 3D/OpenGL performance while a follow-up article this weekend is looking exclusively at the 2D performance. With 2D, for pre-GCN cards on xf86-video-ati it means having EXA acceleration by default (or manually switching to GLAMOR via the xorg.conf) where as xf86-video-modesetting is a universal driver that requires GLAMOR for doing 2D acceleration over OpenGL.
From the quick tests done of DRI2 vs. DRI3 with the Cayman GPU then switching over to the Modesetting DDX on Ubuntu 16.04, you can find the data via this OpenBenchmarking.org result file along with all of the system details.
Long story short, the modesetting results tend to be very close to that of xf86-video-ati for 3D/GL results, which is an improvement over some of the earlier data on this generic DDX driver when it was much less mature. Again, 2D data coming later today or tomorrow.
If you are curious on the functionality differences between these two DDX drivers, see the bug report on Ditching xf86-video-ati in favor of xf86-video-modesetting?. AMD's Alex Deucher basically explained, "Older chips don't have the necessary functionality to support glamor. They still need the asic specific acceleration code. R600 and newer could eventually move to -modesetting once all the features from -ati get ported to -modesetting." There's also been a similar DDX discussion on the Nouveau side.