Mesa Git Yields Performance Improvements For Newer AMD GPUs

With Tesseract there wasn't much in the way of performance changes to find except for the Radeon R9 270X that was still performing strange on this setup.

The Team Fortress 2 performance was largely unchanged -- ignoring the Radeon R9 270X -- except that the HD 7950 did seem to regress for this popular Valve free-to-play game.

Unigine Tropics was faster for the newer AMD GCN GPUs using the RadeonSI Gallium3D driver while the performance was lower with Mesa 10.5-devel for the two tested Radeon HD 6000 series GPUs on the R600g driver.

Warsow was faster with the newer GCN GPUs while it ended up being unchanged for the older Northern Islands GPUs.