Of course, this only works for drivers which exist both in a classic and gallium version. At the time of writing these are:
- i915, i965: The gallium drivers for Intel chipsets are presently inferior to the classic drivers. There is little reason to use them at this time.
- Radeon r300: The radeong gallium driver works well and has recently surpassed the classic driver in terms of features and performance.
- Radeon r600: The r600g gallium driver was added to mesa a week ago and does not do anything useful yet.
- Software renderer: If Mesa was built with the "llvm" USE flag enabled, then the gallium llvmpipe driver will give you much improved performance over the classic software rasterizer. As a tile based renderer it will use multithreading too. However some graphical glitches are still visible.
Update: If you had already installed mesa-9999 from the X11 overlay, please rebuild it to ensure proper functioning of the eselect module.