Likely Radeon Gallium3D Regression On Linux 3.14 + Mesa 10.2
For anyone currently experiencing a slowdown of their Radeon Gallium3D open-source driver stack or are interested in helping out track down a new performance issue, it appears the Linux 3.14 + Mesa 10.2 configuration is regressing on Ubuntu 14.04 LTS in place of Linux 3.13 + Mesa 10.1.
After running a 13-way R600/RadeonSI Gallium3D comparison a few days ago, I was continuing that comparison by comparing the tested Linux 3.13 + Mesa 10.1 configuration against the Linux 3.14 Git kernel with Mesa 10.2-devel Git. Fairly soon into the latest Radeon driver testing I noticed problems: OpenGL performance drops nearly across the board.
Compared to the Ubuntu 14.04 stock configuration that was used in the original 13-way graphics card comparison, the only system changes made since then were upgrading to the latest xorg-edgers packages that provided Mesa 10.2-devel and xf86-video-ati 7.3.99 and then installing the Ubuntu mainline kernel 3.14 package. Both of these upgrades were done on 27 February.
With the upgrade to the newer code, for many OpenGL benchmarks there's now a significant drop in performance for the five tested graphics cards (thus far) compared to the Linux 3.13 + Mesa 10.1 stable state. I'm mentioning this now in case anyone else has encountered similar issues with the newer code or looking to try a similar comparison on your own systems in hopes of spotting the issue. I'll likely get around to digging deeper in a few days time (and depending upon what other Phoronix readers report in as their experiences) to find out of it's a Mesa or kernel issue but as my time is already stretched very thin, that work unfortunately has to be punted to the back-burner until finding extra time or resources to dig deeper into this likely regression.
Here are the results thus far illustrating the problems with the newer code.