https://bugs.freedesktop.org/show_bug.cgi?id=57567
--- Comment #22 from Vladimir bobahu4@gmail.com --- I've just tested vanilla 3.9-rc5, to be sure that it's actually your patch that make things a little bit better, not 3.9 kernel itself.
unpatched 3.9-rc5 - same ersult as 3.7/3.8 kernel, so yeah, it's definetly a patch.