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([2600:380:4a5b:8858:a8b3:edff:f3de:ccc1]) by smtp.gmail.com with ESMTPSA id q75sm18837797pfa.38.2019.02.11.18.51.28 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Feb 2019 18:51:29 -0800 (PST) Subject: Re: [PATCH V2] blk-mq: insert rq with DONTPREP to hctx dispatch list when requeue To: Jianchao Wang Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <1549936585-1702-1-git-send-email-jianchao.w.wang@oracle.com> From: Jens Axboe Message-ID: <077964ab-0502-49ab-132d-657d32df7461@kernel.dk> Date: Mon, 11 Feb 2019 19:51:27 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <1549936585-1702-1-git-send-email-jianchao.w.wang@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/11/19 6:56 PM, Jianchao Wang wrote: > When requeue, if RQF_DONTPREP, rq has contained some driver > specific data, so insert it to hctx dispatch list to avoid any > merge. Take scsi as example, here is the trace event log (no > io scheduler, because RQF_STARTED would prevent merging), > > kworker/0:1H-339 [000] ...1 2037.209289: block_rq_insert: 8,0 R 4096 () 32768 + 8 [kworker/0:1H] > scsi_inert_test-1987 [000] .... 2037.220465: block_bio_queue: 8,0 R 32776 + 8 [scsi_inert_test] > scsi_inert_test-1987 [000] ...2 2037.220466: block_bio_backmerge: 8,0 R 32776 + 8 [scsi_inert_test] > kworker/0:1H-339 [000] .... 2047.220913: block_rq_issue: 8,0 R 8192 () 32768 + 16 [kworker/0:1H] > scsi_inert_test-1996 [000] ..s1 2047.221007: block_rq_complete: 8,0 R () 32768 + 8 [0] > scsi_inert_test-1996 [000] .Ns1 2047.221045: block_rq_requeue: 8,0 R () 32776 + 8 [0] > kworker/0:1H-339 [000] ...1 2047.221054: block_rq_insert: 8,0 R 4096 () 32776 + 8 [kworker/0:1H] > kworker/0:1H-339 [000] ...1 2047.221056: block_rq_issue: 8,0 R 4096 () 32776 + 8 [kworker/0:1H] > scsi_inert_test-1986 [000] ..s1 2047.221119: block_rq_complete: 8,0 R () 32776 + 8 [0] > > (32768 + 8) was requeued by scsi_queue_insert and had RQF_DONTPREP. > Then it was merged with (32776 + 8) and issued. Due to RQF_DONTPREP, > the sdb only contained the part of (32768 + 8), then only that part > was completed. The lucky thing was that scsi_io_completion detected > it and requeued the remaining part. So we didn't get corrupted data. > However, the requeue of (32776 + 8) is not expected. Looks good to me, I'll add this for 5.0. -- Jens Axboe