On Tue, Sep 19, 2017 at 11:56:03AM -0400, Mike Snitzer wrote: > On Tue, Sep 19 2017 at 11:36am -0400, > Bart Van Assche <Bart.VanAssche@xxxxxxx> wrote: > > > On Tue, 2017-09-19 at 13:43 +0800, Ming Lei wrote: > > > On Mon, Sep 18, 2017 at 03:18:16PM +0000, Bart Van Assche wrote: > > > > If you are still looking at removing the blk_mq_delay_run_hw_queue() calls > > > > then I think you are looking in the wrong direction. What kind of problem > > > > are you trying to solve? Is it perhaps that there can be a delay between > > > > > > Actually the improvement on dm-rq IO schedule(the patch 2 ~ 5) doesn't > > > need this patch. > > > > The approach of this patch series looks wrong to me and patch 5/5 is an ugly > > hack in my opinion. That's why I asked you to drop the entire patch series and > > to test whether inserting a queue run call into the dm-mpath end_io callback > > yields a similar performance improvement to the patches you posted. Please do > > not expect me to spend more time on this patch series if you do not come up > > with measurement results for the proposed alternative. > > Bart, asserting that Ming's work is a hack doesn't help your apparent > goal of deligitimizing Ming's work. > > Nor does it take away from the fact that your indecision on appropriate > timeouts (let alone ability to defend and/or explain them) validates > Ming calling them into question (which you are now dodging regularly). > > But please don't take this feedback and shut-down. Instead please work > together more constructively. This doesn't need to be adversarial! I > am at a loss for why there is such animosity from your end Bart. > > Please dial it back. It is just a distraction that fosters needless > in-fighting. > > Believe it or not: Ming is just trying to improve the code because he > has a testbed that is showing fairly abysmal performance with dm-mq > multipath (on lpfc with scsi-mq). > > Ming, if you can: please see if what Bart has proposed (instead: run > queue at end_io) helps. Though I don't yet see why that should be > needed. Run queue at end_io is definitely wrong, because blk-mq has SCHED_RESTART to do that already. The dm-mpath performance issue is nothing to do with that, actually the issue is very similar with my improvement on SCSI-MQ, because now dm_dispatch_clone_request() doesn't know if the underlying queue is busy or not, and dm-rq/mpath is just trying to dispatch more request to underlying queue even though it is busy, then IO merge can't be done easily on dm-rq/mpath. I am thinking another way to improve this issue, since some SCSI device's queue_depth is different with .cmd_per_lun, will post patchset soon. -- Ming
