On 3/22/22 8:10 PM, Ming Lei wrote: > 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? My point is that it is, since submission is through io_uring which does exactly that. -- Jens Axboe
