https://bugs.freedesktop.org/show_bug.cgi?id=79842
--- Comment #4 from Grigori Goronzy greg@chown.ath.cx --- Probably related to this:
http://cgit.freedesktop.org/mesa/mesa/commit/?h=10.1&id=1ba2298131924daf...
Anisotropic filtering was broken in radeonsi, and that fixed it. Anisotropic filtering has some overhead, which explains the slightly reduced performance.
This patch was applied to 10.1 and 10.2 branches as well as master.