From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4ECCCC43381 for ; Fri, 15 Feb 2019 03:14:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1D2E02192B for ; Fri, 15 Feb 2019 03:14:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727397AbfBODOO (ORCPT ); Thu, 14 Feb 2019 22:14:14 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56776 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726010AbfBODOO (ORCPT ); Thu, 14 Feb 2019 22:14:14 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BAB80368E7; Fri, 15 Feb 2019 03:14:13 +0000 (UTC) Received: from ming.t460p (ovpn-8-28.pek2.redhat.com [10.72.8.28]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CF39360A9D; Fri, 15 Feb 2019 03:14:06 +0000 (UTC) Date: Fri, 15 Feb 2019 11:14:02 +0800 From: Ming Lei To: "jianchao.wang" Cc: axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Damien Le Moal Subject: Re: [PATCH V2] blk-mq: insert rq with DONTPREP to hctx dispatch list when requeue Message-ID: <20190215031401.GD21045@ming.t460p> References: <1549936585-1702-1-git-send-email-jianchao.w.wang@oracle.com> <20190215020049.GA21045@ming.t460p> <07260476-307a-efdc-63aa-95ea0a3e7489@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <07260476-307a-efdc-63aa-95ea0a3e7489@oracle.com> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Fri, 15 Feb 2019 03:14:13 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Feb 15, 2019 at 10:34:39AM +0800, jianchao.wang wrote: > Hi Ming > > Thanks for your kindly response. > > On 2/15/19 10:00 AM, Ming Lei wrote: > > On Tue, Feb 12, 2019 at 09:56:25AM +0800, 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. > > > > scsi_mq_requeue_cmd() does uninit the request before requeuing, but > > __scsi_queue_insert doesn't do that. > > Yes. > scsi layer use both of them. > > > > > > >> 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. > >> > >> Suggested-by: Jens Axboe > >> Signed-off-by: Jianchao Wang > >> --- > >> V2: > >> - refactor the code based on Jens' suggestion > >> > >> block/blk-mq.c | 12 ++++++++++-- > >> 1 file changed, 10 insertions(+), 2 deletions(-) > >> > >> diff --git a/block/blk-mq.c b/block/blk-mq.c > >> index 8f5b533..9437a5e 100644 > >> --- a/block/blk-mq.c > >> +++ b/block/blk-mq.c > >> @@ -737,12 +737,20 @@ static void blk_mq_requeue_work(struct work_struct *work) > >> spin_unlock_irq(&q->requeue_lock); > >> > >> list_for_each_entry_safe(rq, next, &rq_list, queuelist) { > >> - if (!(rq->rq_flags & RQF_SOFTBARRIER)) > >> + if (!(rq->rq_flags & (RQF_SOFTBARRIER | RQF_DONTPREP))) > >> continue; > >> > >> rq->rq_flags &= ~RQF_SOFTBARRIER; > >> list_del_init(&rq->queuelist); > >> - blk_mq_sched_insert_request(rq, true, false, false); > >> + /* > >> + * If RQF_DONTPREP, rq has contained some driver specific > >> + * data, so insert it to hctx dispatch list to avoid any > >> + * merge. > >> + */ > >> + if (rq->rq_flags & RQF_DONTPREP) > >> + blk_mq_request_bypass_insert(rq, false); > >> + else > >> + blk_mq_sched_insert_request(rq, true, false, false); > >> } > > > > Suppose it is one WRITE request to zone device, this way might break > > the order. > > I'm not sure about this. > Since the request is dispatched, it should hold and zone write lock. > And also mq-deadline doesn't have a .requeue_request, zone write lock > wouldn't be released during requeue. You are right, looks I misunderstood the zone write lock, sorry for the noise. > > IMO, this requeue action is similar with what blk_mq_dispatch_rq_list does. > The latter one also issues the request to underlying driver and requeue rqs > on dispatch_list if get BLK_STS_SOURCE or BLK_STS_DEV_SOURCE. > > And in addition, RQF_STARTED is set by io scheduler .dispatch_request and > it could be stop merging as RQF_NOMERGE_FLAGS contains it. Yes, that is correct. Then another question is: Why don't always requeue request in this way so that it can be simplified into one code path? 1) in block legacy code, blk_requeue_request() doesn't insert the request into scheduler queue, and simply put the request into q->queue_head. 2) blk_mq_requeue_request() is basically run from completion context for handling very unusual cases(partial completion, error, timeout, ...), and there shouldn't have benefit to schedule/merge requeued request. 3) RQF_DONTPREP is like a driver private flag, and read/write by driver only before this patch. Thanks, Ming