Maybe watching what the workqueue is doing using the following trace events could be helpful.
# grep workqueue /sys/kernel/debug/tracing/available_events workqueue:workqueue_insertion workqueue:workqueue_execution workqueue:workqueue_creation workqueue:workqueue_destruction
Since I've never done this before, I will tell you how I captured the trace so you know what I did and can see whether I did something wrong and can correct me if necessary. echo blk > /sys/kernel/debug/tracing/current_tracer echo 1 > /sys/block/sdb/trace/enable echo workqueue_queue_work >> /sys/kernel/debug/tracing/set_event echo workqueue_activate_work >> /sys/kernel/debug/tracing/set_event echo workqueue_execute_start >> /sys/kernel/debug/tracing/set_event echo workqueue_execute_end >> /sys/kernel/debug/tracing/set_event cat /sys/kernel/debug/tracing/trace_pipe And that output i gzip'd. This was taken with 2.6.37 plus the patch you mentioned on a Dell R815 with 2 12 core AMD Opteron 6174 CPUs. If you need any more information, please let me know. Regards Dominik