From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Lei Subject: Re: [PATCH V5 8/8] blk-mq: improve bio merge from blk-mq sw queue Date: Mon, 9 Oct 2017 12:28:37 +0800 Message-ID: <20171009042835.GA19029@ming.t460p> References: <20170930112655.31451-1-ming.lei@redhat.com> <20170930112655.31451-9-ming.lei@redhat.com> <20171003092143.GF2771@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20171003092143.GF2771@infradead.org> Sender: linux-block-owner@vger.kernel.org To: Christoph Hellwig Cc: Jens Axboe , linux-block@vger.kernel.org, Mike Snitzer , dm-devel@redhat.com, Bart Van Assche , Laurence Oberman , Paolo Valente , Oleksandr Natalenko , Tom Nguyen , linux-kernel@vger.kernel.org, Omar Sandoval List-Id: dm-devel.ids On Tue, Oct 03, 2017 at 02:21:43AM -0700, Christoph Hellwig wrote: > This looks generally good to me, but I really worry about the impact > on very high iops devices. Did you try this e.g. for random reads > from unallocated blocks on an enterprise NVMe SSD? Looks no such impact, please see the following data in the fio test(libaio, direct, bs=4k, 64jobs, randread, none scheduler) [root@storageqe-62 results]# ../parse_fio 4.14.0-rc2.no_blk_mq_perf+-nvme-64jobs-mq-none.log 4.14.0-rc2.BLK_MQ_PERF_V5+-nvme-64jobs-mq-none.log --------------------------------------- IOPS(K) | NONE | NONE --------------------------------------- randread | 650.98 | 653.15 --------------------------------------- OR: If you worry about this impact, can we simply disable merge on NVMe for none scheduler? It is basically impossible to merge NVMe's request/bio when none is used, but it can be doable in case of kyber scheduler. -- Ming