https://bugs.freedesktop.org/show_bug.cgi?id=56634
--- Comment #1 from Andy Furniss lists@andyfurniss.entadsl.com --- I see some slowdowns with etqw (can't test heaven) on HD4890 that seem to be caused by this.
It's not constant - in fact mostly etqw with current head is the fastest I've ever seen it.
It may, however, during a short timenetdemo just suddenly drop to 4fps for a few seconds, or it may start slow ~10fps then go full speed.
With this reverted I haven't seen any slowdowns (yet).