As a result of Jens' global unplug work we've had to revist all the uses of blk_run_queues(), and be specific about which queues we need to run. In a lot of cases I've just knocked them out completely where they appear to be hangovers from 2.4 weirdness. If you start getting lumpy io with multipath, snapshots or mirroring this is probably the reason - please yell.