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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 8E19DC43381 for ; Fri, 15 Feb 2019 03:39:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4BFDB20836 for ; Fri, 15 Feb 2019 03:39:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="zHNn4JAs" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730264AbfBODjL (ORCPT ); Thu, 14 Feb 2019 22:39:11 -0500 Received: from userp2130.oracle.com ([156.151.31.86]:40118 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726010AbfBODjL (ORCPT ); Thu, 14 Feb 2019 22:39:11 -0500 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x1F3cjb2010008; Fri, 15 Feb 2019 03:39:05 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=OxLfLn0OqCm+09E7Z+vz/hjCwnW23QMenkiBNtawLqM=; b=zHNn4JAsxKqIbz+6xVTSM6TksKnHLp8QC1U0WDnvdczgokQp2InwSkTjvJ3lC+U4zrp8 G6MGWqxjkw6/yo7rBb9OO9OO4Paqt03N/YO+EMs7BmADRdQHkaKbsHwgh8BCAFhsIZCH hAhN1qQywrNP8VbSJpq3nGHLfFgkOlGrGBqSgmHGskanU0ad1kWyRMquT0vkQZxHsKp7 HhgRLiEOcD/27k/9JohsWSkBl7snkQVZZcC8CDk3w1Cof2Cw3k3L74MGKMFwedIk8BmH fQdGoxH1S6FZxq7qszztr4+h4js5jCHm7Uy++S7+++phcOujsk3rzTlBmNqCc4MbQfZ1 bg== Received: from userv0022.oracle.com (userv0022.oracle.com [156.151.31.74]) by userp2130.oracle.com with ESMTP id 2qhrekuge3-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 15 Feb 2019 03:39:05 +0000 Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by userv0022.oracle.com (8.14.4/8.14.4) with ESMTP id x1F3d4PO006075 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 15 Feb 2019 03:39:04 GMT Received: from abhmp0006.oracle.com (abhmp0006.oracle.com [141.146.116.12]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x1F3d3p4006030; Fri, 15 Feb 2019 03:39:03 GMT Received: from [10.182.71.8] (/10.182.71.8) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 15 Feb 2019 03:39:03 +0000 Subject: Re: [PATCH V2] blk-mq: insert rq with DONTPREP to hctx dispatch list when requeue To: Ming Lei Cc: axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Damien Le Moal References: <1549936585-1702-1-git-send-email-jianchao.w.wang@oracle.com> <20190215020049.GA21045@ming.t460p> <07260476-307a-efdc-63aa-95ea0a3e7489@oracle.com> <20190215031401.GD21045@ming.t460p> From: "jianchao.wang" Message-ID: <85432d26-22de-fa87-67d3-4292f780d5aa@oracle.com> Date: Fri, 15 Feb 2019 11:41:25 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20190215031401.GD21045@ming.t460p> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9167 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1902150024 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2/15/19 11:14 AM, Ming Lei wrote: > 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. Actually, I'm also confused about questions above when I looked into the code before :) > > 3) RQF_DONTPREP is like a driver private flag, and read/write by driver > only before this patch. Yes, indeed. And it tells us there is driver specific data in the request. Thanks Jianchao