The commit that appeared in Mesa Git master last night ahead of Mesa 10.0 is a change to try to avoid GPU stalls when calling the glBufferSubData() function. Eric Anholt of Intel's Open-Source Technology Center who did this commit had noted, "On DOTA2, framerate on dota2-de1.dem in windowed mode on my laptop improves by 7.69854% +/- 0.909163% (n=3). In a microbenchmark hitting this code path (wall time of piglit vbo-subdata-many), runtime decreases from 0.8 to 0.05 seconds."
About an eight percent performance improvement for Dota 2 on the open-source Intel Linux graphics driver will certainly be appreciated by many Steam Linux gamers. This driver performance optimization happened via this Git commit.