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Tue, 14 Apr 2026 20:02:49 +0000 From: Aaron Tomlin To: corbet@lwn.net, skhan@linuxfoundation.org Cc: tglx@kernel.org, akpm@linux-foundation.org, bp@alien8.de, rdunlap@infradead.org, dave.hansen@linux.intel.com, feng.tang@linux.alibaba.com, pawan.kumar.gupta@linux.intel.com, dapeng1.mi@linux.intel.com, kees@kernel.org, elver@google.com, paulmck@kernel.org, lirongqing@baidu.com, bhelgaas@google.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] docs: kernel-parameters: document scope of irqaffinity= parameter Date: Tue, 14 Apr 2026 16:02:45 -0400 Message-ID: <20260414200245.1153919-1-atomlin@atomlin.com> X-Mailer: git-send-email 2.51.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: BL1PR13CA0160.namprd13.prod.outlook.com (2603:10b6:208:2bd::15) 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_|CWLP123MB2753:EE_ X-MS-Office365-Filtering-Correlation-Id: f7adde86-1305-4fe2-797e-08de9a60cdf2 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014|56012099003|18002099003; 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However, there is a widespread misconception that "irqaffinity=" acts as a global, absolute override for all hardware interrupts. In reality, "irqaffinity=" strictly populates the irq_default_affinity mask. When the kernel allocates multiqueue vectors (e.g., irq_create_affinity_masks()), it explicitly bypasses this default mask for managed interrupts. Instead, it relies on dynamic spreading algorithms to map queues to the available topology, effectively overriding any default the administrator set via the command line. This patch explicitly documents this limitation in kernel-parameters.txt to set correct expectations and directs users to the appropriate "isolcpus=" sub-parameters for managed interrupt isolation. Signed-off-by: Aaron Tomlin --- Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 9ed7c3ecd158..40ca92d8cf04 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2732,6 +2732,14 @@ Kernel parameters irqaffinity= [SMP] Set the default irq affinity mask The argument is a cpu list, as described above. + Note: This parameter only sets the default affinity + for unmanaged interrupts (e.g., legacy single-queue + devices or unmanaged pre/post vectors). It is + explicitly ignored by managed interrupts, such as + those utilised by modern multiqueue storage + controllers. To isolate CPUs from managed + interrupts, see the "managed_irq". + irqchip.gicv2_force_probe= [ARM,ARM64,EARLY] Format: -- 2.51.0