Is Upgrading To Mesa 11.1-devel Worthwhile For Radeon R600g Users?
Upgrading the user-space graphics stack for RadeonSI users is easy thanks to the Padoka PPA for Ubuntu 15.10 that provides routine Mesa Git snapshots built against the AMDGPU LLVM SVN back-end too. As shown in other articles, RadeonSI with Mesa Git is great and tends to deliver better functionality and performance than the stable releases given that RadeonSI is still advancing -- on Ubuntu 15.10, it's a difference of OpenGL 3.3 vs. 4.1.
With the Radeon R600g driver that supports the Radeon HD 6000 series graphics cards and older, that open-source driver has reached a mature state... With the open-source AMD developers busy on RadeonSI and other newer hardware support, it doesn't receive as much attention from them, but there is still some work being done by the community. R600g upstream still only supports OpenGL 3.3, but it's slowly catching up with OpenGL 4 support.
On my AMD FirePro V7900 system with Cayman GPU, I did some quick tests this weekend comparing Ubuntu 15.10 out-of-the-box and then enabling the Padoka PPA as well as moving to the Linux 4.3 kernel. Long story short, no measurable OpenGL performance changes. Perhaps in the weeks ahead it will become more worthwhile for those with these old, pre-GCN GPUs to move to Mesa Git, but for now it doesn't offer any real performance difference I've found compared to Mesa 11.0. There's also the daily Mesa benchmarks done at LinuxBenhcmarking.com and there haven't been anything major to note for the HD 6770 system in the server room.
Of course, once there are R600g performance improvements or OpenGL 4.0~4.1 compliance reached, you can expect to read about it on Phoronix. If you want to ride the latest open-source graphics code anyway, you can try the Padoka PPA for Ubuntu 15.10 and the Ubuntu Mainline Kernel archive makes it easy to grab new release candidates and daily snapshots (along with DRM-Next) of the mainline Linux kernel if needing a newer Radeon DRM driver.