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Thu, 16 Apr 2026 19:30:39 +0000 From: Aaron Tomlin To: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, mst@redhat.com Cc: atomlin@atomlin.com, aacraid@microsemi.com, James.Bottomley@HansenPartnership.com, martin.petersen@oracle.com, liyihang9@h-partners.com, kashyap.desai@broadcom.com, sumit.saxena@broadcom.com, shivasharan.srikanteshwara@broadcom.com, chandrakanth.patil@broadcom.com, sathya.prakash@broadcom.com, sreekanth.reddy@broadcom.com, suganath-prabu.subramani@broadcom.com, ranjan.kumar@broadcom.com, jinpu.wang@cloud.ionos.com, tglx@kernel.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, akpm@linux-foundation.org, maz@kernel.org, ruanjinjie@huawei.com, bigeasy@linutronix.de, yphbchou0911@gmail.com, wagi@kernel.org, frederic@kernel.org, longman@redhat.com, chenridong@huawei.com, hare@suse.de, kch@nvidia.com, ming.lei@redhat.com, tom.leiming@gmail.com, steve@abita.co, sean@ashe.io, chjohnst@gmail.com, neelx@suse.com, mproche@gmail.com, nick.lange@gmail.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, megaraidlinux.pdl@broadcom.com, mpi3mr-linuxdrv.pdl@broadcom.com, MPT-FusionLinux.pdl@broadcom.com Subject: [PATCH v11 13/13] docs: add io_queue flag to isolcpus Date: Thu, 16 Apr 2026 15:29:42 -0400 Message-ID: <20260416192942.1243421-14-atomlin@atomlin.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260416192942.1243421-1-atomlin@atomlin.com> References: <20260416192942.1243421-1-atomlin@atomlin.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: MN2PR15CA0039.namprd15.prod.outlook.com (2603:10b6:208:237::8) To CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM (2603:10a6:400:70::10) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CWLP123MB3523:EE_|CWXP123MB4039:EE_ X-MS-Office365-Filtering-Correlation-Id: 38982782-3011-47ac-5979-08de9beea27e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016|56012099003|18002099003|22082099003; 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Document this new flag in the isolcpus command-line argument description. Signed-off-by: Daniel Wagner Reviewed-by: Hannes Reinecke [atomlin: Refined io_queue kernel parameter documentation] Signed-off-by: Aaron Tomlin --- .../admin-guide/kernel-parameters.txt | 30 ++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 4510b4b3c416..52ede95db56f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2827,7 +2827,6 @@ Kernel parameters "number of CPUs in system - 1". managed_irq - Isolate from being targeted by managed interrupts which have an interrupt mask containing isolated CPUs. The affinity of managed interrupts is @@ -2850,6 +2849,35 @@ Kernel parameters housekeeping CPUs has no influence on those queues. + io_queue + Applicable to managed IRQs only. Restrict + multiqueue hardware queue allocation to online + housekeeping CPUs. This guarantees that all + managed hardware completion interrupts are routed + exclusively to housekeeping cores, shielding + isolated CPUs from I/O interruptions even if they + initiated the request. + + The io_queue configuration takes precedence over + managed_irq. When io_queue is used, managed_irq + placement constraints have no effect. + + Note: Using io_queue restricts the number of + allocated hardware queues to match the number of + housekeeping CPUs. This prevents MSI-X vector + exhaustion and forces isolated CPUs to share + submission queues. + + Note: Offlining housekeeping CPUs which serve + isolated CPUs will fail. The isolated CPUs must + be offlined before offlining the housekeeping + CPUs. + + Note: When I/O is submitted by an application on + an isolated CPU, the hardware completion + interrupt is handled entirely by a housekeeping + CPU. + The format of is described above. iucv= [HW,NET] -- 2.51.0