The Most Comprehensive AMD Radeon Linux Graphics Comparison
AMD's open-source work force is limited. There is John Bridgman who is the wrangler within AMD to work on documentation and communicating between the various departments. John's also the official AMD open-source communicator to the Phoronix Forums, where he's the most active individual in the entire forums with nearing 6,000 posts and is very helpful in providing technical support to AMD's desktop Linux customers, valuable insight on future open-source work, and even for sharing his wonderful cooking recipes.
John has been a long-time employee from the ATI days while by his side since the start of the open-source efforts has been Alex Deucher, who has long worked on the open-source ATI driver and was then hired by AMD for this strategy. AMD's original partners on the open-source effort also included Novell/SUSE, but they eventually parted ways. Most recently, AMD hired two new developers that were veteran open-source contributors. While the official open-source staff is about four people at AMD, there is the open-source community, with many prolific contributors such as Marek Olsak.
Fortunately, the rest of the support remained in fairly good shape for the previous generations of ATI/AMD Radeon hardware with the Linux 3.1 kernel, Mesa 7.12-devel git-0b66610, and xf86-video-ati 6.14.99, all of which were built freshly from Git in late August. An fglrx 8.90 (Catalyst ~11.10) press driver was used for this testing in order to attain Linux 3.1 kernel compatibility so that this comparison could be done without having to switch kernels between drivers, for more accurate results. The Catalyst OpenGL version string was 4.1.11149 for the modern ASICs while the older hardware not supportive of GL4 was at OpenGL 3.3.11149.
On the open-source Radeon side, swap buffers wait was disabled and color tiling was enabled for all hardware. These are known performance tweaks for this driver. Color tiling is enabled for some ASICs by default, but due to bugs, it is not on by default for all hardware but can be toggled via the xorg.conf. Swap buffers wait is enabled by default as it can reduce screen tearing, but it comes at the cost of frame-rates.
For those curious about the compatibility of the open-source Radeon driver stack, on the Wiki are the Radeon Feature and Radeon Program pages that document the commonly supported features for each generation and the known programs that work and don't work for each hardware generation, as reported by end-users. Besides the OpenGL benchmarks with problems talked about in this article, there's many other games and OpenGL applications out there, some of which will only work with the very latest Git, is still garbage, or requires other steps (such as for games that explicitly depend upon S3TC texture compression). Performance is also another story.