Alex Deucher committed a change this morning to xf86-video-ati that re-enables tiling by default for "CIK" / Sea Islands GPUs up through the latest Hawaii hardware. Alex noted in the commit, "Now that mesa 10.1 is released, we can enable this by default for CIK parts. Tiling improves memory bandwidth utilization."
Tiling tends to be a big performance win for many OpenGL games so it's good to see this feature restored in the open-source driver. The DDX update is also mandating a new version of libdrm for proper CIK tiling support. If you are curious about open-source OpenGL performance expectations for modern AMD GPUs, see our recent 13-way R600/RadeonSI GPU comparison done from Ubuntu Linux 14.04 LTS.