On Wed, 2017-09-20 at 06:44 +0800, Ming Lei wrote: > For this issue, it isn't same between SCSI and dm-rq. > > We don't need to run queue in .end_io of dm, and the theory is > simple, otherwise it isn't performance issue, and should be I/O hang. > > 1) every dm-rq's request is 1:1 mapped to SCSI's request > > 2) if there is any mapped SCSI request not finished, either > in-flight or in requeue list or whatever, there will be one > corresponding dm-rq's request in-flight > > 3) once the mapped SCSI request is completed, dm-rq's completion > path will be triggered and dm-rq's queue will be rerun because of > SCHED_RESTART in dm-rq > > So the hw queue of dm-rq has been run in dm-rq's completion path > already, right? Why do we need to do it again in the hot path? The measurement data in the description of patch 5/5 shows a significant performance regression for an important workload, namely random I/O. Additionally, the performance improvement for sequential I/O was achieved for an unrealistically low queue depth. Sorry but given these measurement results I don't see why I should spend more time on this patch series. Bart.
