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Tue, 3 Nov 2026 17:04:46 +0000 (GMT) Received: from [9.61.129.51] (unknown [9.61.129.51]) by smtpav01.dal12v.mail.ibm.com (Postfix) with ESMTP; Tue, 3 Nov 2026 17:04:46 +0000 (GMT) Message-ID: <7f6e7fc6-dd40-4949-9a1b-95200c9680e6@linux.ibm.com> Date: Tue, 3 Nov 2026 22:34:44 +0530 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] blk-mq: use a housekeeping CPU for passthrough requests on isolated hctxs To: Daniel Wagner , Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg Cc: Ming Lei , Surabhi Gogte , Hannes Reinecke , Frederic Weisbecker , Aaron Tomlin , Maurizio Lombardi , Sebastian Andrzej Siewior , linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org References: <20261103-nvme-fabrics-isolcpu-v2-1-95ec70d58254@suse.de> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20261103-nvme-fabrics-isolcpu-v2-1-95ec70d58254@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: d-Nw3Q3zP_MAaZ7sH5O-WlJu5ENMXRp0 X-Proofpoint-Spam-Info: AW1haW4tMjYxMTAzMDA2NiBTYWx0ZWRfX5UilMRvmKMZd oVFVkprwMWWs6xXsiE5HNVLR6Cixz5ZoyDx5AUN3gx1p33X8kzLum/roaNDJESDUBD4IXdxdlgL xDyIKNz4YUkwDPdBCEHLKNttcPpTF6I= X-Authority-Analysis: v=2.4 cv=LokHWXdc c=1 sm=1 tr=0 ts=6aea1433 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=20KFwNOVAAAA:8 a=VnNF1IyMAAAA:8 a=Xo84benzLQ6E682cTSsA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTAzMDA2NiBTYWx0ZWRfX8fV48+h9Df/T dR/Uq0WBQAYrS8YxaMPDscPYGtROOj9C5Jlk+TCaCZ6A+TeOUjtGFORrPwMvzy0U+52t7U+I6Qe khYwhOND4JK0bja1yyKwlFdZyYRwR5NseCuRaDUR3JNmr54bmLIjbfIH6qPvfq4hZiThMCtuX8c oqPlKQh7YBdBN/4dM4z8jlqm4PXbnZi8hESHterSA86BXet99DCanySnItezE73V2hniSO6TjJ8 APZKtmsU/k4KBBnEinCmYElvyKjD/jId6eCpHINOQ0p8781qgmKRx4vzDNmEPC5HhVVDrwPmFq8 iu4faUNrkR9rFTb0zubDzZszAWhTqAKTSOPpNhksZxYc01+k06AX67qE8IZm6dQcog2xGxTLq7g cFn8krnF3Yhs65D1UukBqNgYDhP/ZTYWYnLaGIgiGPcYeQb6AJ6V0LgHDxw2xJxG46TxUFbMAcw kfBo/uE01IlJOMqHvYg== X-Proofpoint-GUID: d-Nw3Q3zP_MAaZ7sH5O-WlJu5ENMXRp0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-03_03,2026-11-03_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 lowpriorityscore=0 clxscore=1011 impostorscore=0 priorityscore=1501 suspectscore=0 phishscore=0 malwarescore=0 bulkscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610300000 definitions=main-2611030066 On 11/3/26 8:27 PM, Daniel Wagner wrote: > blk_mq_alloc_request_hctx uses the first online CPU in hctx->cpumask to > select the software context for a request. > > Since commit a46c27026da1 ("blk-mq: don't schedule block kworker on > isolated CPUs"), hctx->cpumask excludes isolated CPUs. If a hardware > context is mapped only to isolated CPUs, the mask is empty and > blk_mq_alloc_request_hctx fails with -EXDEV. > > The NVMe fabrics transports use blk_mq_alloc_request_hctx to allocate > the Connect command for each I/O queue. As a result, connecting to a > controller can fail when using isolcpus=domain or an isolated cpuset > partition. > > Passthrough requests bypass the software queues and go directly to > hctx->dispatch. Their software context is only used to select the > completion CPU and as a hint when freeing the tag. > > Use the software context of an online housekeeping CPU for passthrough > requests. > > Fixes: a46c27026da1 ("blk-mq: don't schedule block kworker on isolated CPUs") > Tested-by: Maurizio Lombardi > Signed-off-by: Daniel Wagner Looks good to me: Reviewed-by: Nilay Shroff