https://bugs.freedesktop.org/show_bug.cgi?id=98239
--- Comment #6 from Marek Olšák maraeo@gmail.com --- Doom 3 is limited by the CPU. OpenGL multithreading should help with that. With stock Mesa, there is no way make Doom 3 faster.
When the GPU load is low, it means the app is CPU-bound. Multithreading is the only thing that can help with that.