On Fri, 2017-10-27 at 13:38 +0800, Ming Lei wrote: > On Fri, Oct 27, 2017 at 04:53:18AM +0000, Bart Van Assche wrote: > > On Fri, 2017-10-27 at 12:43 +0800, Ming Lei wrote: > > > The 1st patch removes the RESTART for TAG-SHARED because SCSI handles it > > > by itself, and not necessary to waste CPU to do the expensive RESTART. > > > And Roman Pen reported that this RESTART cuts half of IOPS in his case. > > > > > > The 2nd patch removes the RESTART when .get_budget returns > > > BLK_STS_RESOURCE, > > > and this RESTART is handled by SCSI's RESTART(scsi_end_request()) too. > > > > There are more block drivers than the SCSI core that share tags. If the > > Could you share us what the other in-tree driver which share tags is?
I think the following in-tree drivers support shared tags (in alphabetical order): * null_blk. See also the shared_tags kernel module parameter. * nvme. See also nvme_alloc_ns(). * scsi-mq. Please note that the queue_rq() function of *all* these drivers can return BLK_STS_RESOURCE. > Actually SCSI's RESTART is very thin, and it is just the per-host > starved_list. Do you see any reason that would prevent to move that mechanism from scsi-mq into the blk-mq core? Thanks, Bart.
