Marek Olšák, the open-source developer that's been known for years due to his major optimizations made to the R300/R600 Gallium3D drivers prior to being hired by AMD, has been working on the newer RadeonSI lately. As shown in yesterday's 21-way Linux graphics card comparison, the newer Radeon HD 7000 / HD 8000 / Rx 200 series hardware has a lot of work ahead before the performance will be on par with the R600g driver.
With a set of 10 patches to the Mesa mailing list today, Marek has made the RadeonSI driver performance 75% faster for the RadeonSI driver, or going from 20 FPS to now 35 FPS with these new patches. The patches come down to sharing OpenGL glMapBuffer optimizations from the R600 Gallium3D driver with RadeonSI. The r600_buffer code is now shared with the RadeonSI driver so it can take advantage of currently missing functionality.
The performance-boosting "Southern Islands" patches can be found on Mesa-dev and will surely be merged for the next Mesa release (Mesa 10.1 or 11.0) in three month's time.