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Thu, 23 May 2024 07:01:01 GMT Received: from smtpav04.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4830D58052; Thu, 23 May 2024 07:00:59 +0000 (GMT) Received: from smtpav04.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1853058067; Thu, 23 May 2024 07:00:57 +0000 (GMT) Received: from [9.109.198.166] (unknown [9.109.198.166]) by smtpav04.dal12v.mail.ibm.com (Postfix) with ESMTP; Thu, 23 May 2024 07:00:56 +0000 (GMT) Message-ID: <89dee2dd-bf3a-4f65-aa44-f8360dd597f0@linux.ibm.com> Date: Thu, 23 May 2024 12:30:55 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] nvme-multipath: fix io accounting on failover To: Keith Busch Cc: Keith Busch , hch@lst.de, sagi@grimberg.me, linux-nvme@lists.infradead.org, jmeneghi@redhat.com References: <20240521180712.2423165-1-kbusch@meta.com> <6e01032f-c90e-4f7e-9339-d2782fd60e3f@linux.ibm.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: DBuxE2Wb_taHHJyoPpO_lZ82BWn6aktX X-Proofpoint-ORIG-GUID: Xr3mq_uUcnYJyb6fqwcLKEmnxzJcGaVR X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.650,FMLib:17.12.28.16 definitions=2024-05-23_03,2024-05-22_01,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 priorityscore=1501 mlxlogscore=914 suspectscore=0 adultscore=0 bulkscore=0 malwarescore=0 mlxscore=0 spamscore=0 impostorscore=0 phishscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2405010000 definitions=main-2405230044 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240523_000120_203330_EECB755B X-CRM114-Status: GOOD ( 18.51 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 5/22/24 19:48, Keith Busch wrote: > On Wed, May 22, 2024 at 06:32:11PM +0530, Nilay Shroff wrote: >> >> >> On 5/21/24 23:37, Keith Busch wrote: >>> From: Keith Busch >>> >>> There are io stats accounting that needs to be handled, so don't call >>> blk_mq_end_request() directly. Use the existing nvme_end_req() helper >>> that already handles everything. >>> >> The changes look good however I have a question about why do we retry an IO >> when that IO is cancelled? For instance, when a multipath IO request is cancelled >> (from nvme_cancel_request()) we re-queue the bio in nvme_failover_req(). >> Similarly, for non-multipath request, we do retry request in nvme_retry_req() >> until retries for a request are maxed out by nvme_max_retries. So wouldn't it be >> appropriate to drop the cancelled request instead of retrying? >> >> However, I do understand retrying a request on a different path when we got the >> request completion status specifying the path related error. > > A cancelled request just means the host thinks the target failed to > produce a response. It doesn't mean the host stopped caring about the > command; the host still wants it to succeed, but determined corrective > action is needed to reclaim and resubmit the command. > Thank Keith, got it! --Nilay