On Tue, Mar 22, 2022 at 07:58:25PM -0600, Jens Axboe wrote: > On 3/22/22 7:41 PM, Jens Axboe wrote: > > On 3/22/22 7:27 PM, Ming Lei wrote: > >> On Mon, Mar 21, 2022 at 12:32:08PM +0530, Kanchan Joshi wrote: > >>> On Mon, Mar 14, 2022 at 10:40:53PM +0800, Ming Lei wrote: > >>>> On Thu, Mar 10, 2022 at 06:10:08PM +0530, Kanchan Joshi wrote: > >>>>> On Thu, Mar 10, 2022 at 2:04 PM Christoph Hellwig <hch@xxxxxx> wrote: > >>>>>> > >>>>>> On Tue, Mar 08, 2022 at 08:50:58PM +0530, Kanchan Joshi wrote: > >>>>>>> From: Jens Axboe <axboe@xxxxxxxxx> > >>>>>>> > >>>>>>> Add support to use plugging if it is enabled, else use default path. > >>>>>> > >>>>>> The subject and this comment don't really explain what is done, and > >>>>>> also don't mention at all why it is done. > >>>>> > >>>>> Missed out, will fix up. But plugging gave a very good hike to IOPS. > >>>> > >>>> But how does plugging improve IOPS here for passthrough request? Not > >>>> see plug->nr_ios is wired to data.nr_tags in blk_mq_alloc_request(), > >>>> which is called by nvme_submit_user_cmd(). > >>> > >>> Yes, one tag at a time for each request, but none of the request gets > >>> dispatched and instead added to the plug. And when io_uring ends the > >>> plug, the whole batch gets dispatched via ->queue_rqs (otherwise it used > >>> to be via ->queue_rq, one request at a time). > >>> > >>> Only .plug impact looks like this on passthru-randread: > >>> > >>> KIOPS(depth_batch) 1_1 8_2 64_16 128_32 > >>> Without plug 159 496 784 785 > >>> With plug 159 525 991 1044 > >>> > >>> Hope it does clarify. > >> > >> OK, thanks for your confirmation, then the improvement should be from > >> batch submission only. > >> > >> If cached request is enabled, I guess the number could be better. > > > > Yes, my original test patch pre-dates being able to set a submit count, > > it would definitely help improve this case too. The current win is > > indeed just from being able to use ->queue_rqs() rather than single > > submit. > > Actually that is already there through io_uring, nothing extra is > needed. I meant in this patchset that plug->nr_ios isn't wired to data.nr_tags in blk_mq_alloc_request(), which is called by pt request allocation, so looks cached request isn't enabled for pt commands? Thanks, Ming
