The R600 SB back-end can improve OpenGL performance for the open-source AMD Radeon Linux graphics driver. However, this back-end isn't the default as AMD views the future with their LLVM compiler back-end, etc. While it's not the default, those early users of Mesa 9.2 have been quick to play with the performance-enhancing code as it's just a matter of setting the R600_DEBUG=sb environment variable.
For those users of the R600 SB back-end, Vadim merged a number of commits into Mesa Git master today. The commits can be found via a CGit query.
Notable to today's commits is ALU packing work for AMD Radeon HD 6900 "Cayman" GPUs. The R600 SB scheduler/register allocator was designed around Evergreen VLIW-5 hardware and is suboptimal for VLIW-4 hardware, but Girlin has now made some improvements that may benefit Cayman GPUs.
Other commits today include fixes for multi-slot instructions on Cayman, fixing the debug dump code for the scheduler, an initial register allocation fix, and some other items.