Operating system: Ubuntu/Windows
Graphics card: GeForce GTX 1060 3GB/PCIe/SSE2
Slowdown FPS to half with subsurf in last daily build (4th December)
-Open FPS_subsurf_bug.blend with Blender version 1b6a394d862 (4th December) and press play.
Result: the FPS slowdown to half compare with Blender version 895295a9f0c (6th November).
I think that the subsurf modifier is the cause of slowdown FPS.