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. -- Jens Axboe
