From nobody Wed Dec 17 19:17:05 2025 Received: from CWXP265CU008.outbound.protection.outlook.com (mail-ukwestazon11020107.outbound.protection.outlook.com [52.101.195.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C1DDB6BB5B for ; Sat, 11 Oct 2025 01:30:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.195.107 ARC-Seal: i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760146213; cv=fail; b=V+6zd+9kDkEYqkKkpuYF4nzAFOGejQpmL68daOhl7frVh4lPvqG+wxdmjHPktAUOOLIvoCIM4p3yA12zvc4Wwmv8dWfv2mxKJhXI1y5YqibNJoTwarcjv1NMRRnLGCzrXGy0hBfMDKmHaBCM4kQ33AQReOC+jkRoZ/9xX2lPoLM= ARC-Message-Signature: i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760146213; c=relaxed/simple; bh=M+lwAHS3ptyIlGHeovOoyUQto7IJnCVxITpOi+YLPSY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: Content-Type:MIME-Version; b=JRsjheXlefNGttNcfzaXdsgs5+dMpDUAnYgPPwgm7M5cB6V9WGm5XoxBBtOc8tEDM2Nbn/r8s2zjo07e8HV+1njGtgHFtOvAwRI0JBd7m3rnakZlezRCfK2x4i0Mieck443X102gHfY6hvnrUxlWgs4eE1lKB70HQFcMmhe5hPI= ARC-Authentication-Results: i=2; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=atomlin.com; spf=pass smtp.mailfrom=atomlin.com; arc=fail smtp.client-ip=52.101.195.107 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=atomlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=atomlin.com ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=X3BcWZhl/e9k/bJYN+rGd4u/Vbr8jKrU2hXK8IkPBsI3CslpcpAm3Lxj+1kLNR9/fAQ6G6EVOeNdQVJeRfeP/3hwqHSJKp84aUrFwdX0wT+wa/fzA5n2dfrhyEOQ8Onh/t4g9uar/81MMXH/sTbUntmEhlYK0hNDQcatpKDcLYn4toQZmZqw06fy283wIAc+fqm4OqZE6PMXMHzCkybDhPr2MdJItJ0FR7lFRptkZNTuBcDoU909BQETATvC31v1DhX5ZXd+2aEApRj84KbbXWwK5o3ZKV/wv24mJ0euRnNL/+aAkFyAS/RRaA9dKkzv3oIA/oLPg/scgFQKs1bKRA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=EVdNGbs5tu5DeatZn9RRKbama/QCC8MXKJI+BA2P3hc=; b=lkKAyXZGZdNdQcEhk35/cvH4RzYYAnVTtvY7qsNU/nCsGbKcBGo7S6mzbM1rJ8L+TLqtLf1X2ia8OOP34ZGm8Z7pt4I6S4JPX5odTzbCXFaKNYQUz/8eTtlahRokIKJIRKTFKdVUuptvMbV7YNihg94/vxhtpyxrV1U8hIR7Pj1rW6VuAIbAgC2Jv4cQ9t06KYKg8dOVnyOC/L9mgJdF3+EKGBR2wR/2H6OtYDg/mZKuCX6JfYAO372q77H06Ln3MageGGzX9myxfFP7UM38xCMEtVAW/hYB1WUhtKRaEDH+DeJ1OVG8EXu1utSCrQWQn7n3PhW+oAXX0Wx1QzzovA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=atomlin.com; dmarc=pass action=none header.from=atomlin.com; dkim=pass header.d=atomlin.com; arc=none Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=atomlin.com; Received: from CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM (2603:10a6:400:70::10) by CWLP123MB6259.GBRP123.PROD.OUTLOOK.COM (2603:10a6:400:1b3::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9203.10; Sat, 11 Oct 2025 01:30:09 +0000 Received: from CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM ([fe80::de8e:2e4f:6c6:f3bf]) by CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM ([fe80::de8e:2e4f:6c6:f3bf%5]) with mapi id 15.20.9203.009; Sat, 11 Oct 2025 01:30:09 +0000 From: Aaron Tomlin To: gregkh@linuxfoundation.org, nathan@kernel.org, rafael@kernel.org, dakr@kernel.org Cc: riel@surriel.com, frederic@kernel.org, atomlin@atomlin.com, linux-kernel@vger.kernel.org Subject: [PATCH v3 1/1] tick/nohz: Expose housekeeping CPUs in sysfs Date: Fri, 10 Oct 2025 21:28:53 -0400 Message-ID: <20251011012853.7539-2-atomlin@atomlin.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20251011012853.7539-1-atomlin@atomlin.com> References: <20251011012853.7539-1-atomlin@atomlin.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: MN2PR18CA0001.namprd18.prod.outlook.com (2603:10b6:208:23c::6) 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_|CWLP123MB6259:EE_ X-MS-Office365-Filtering-Correlation-Id: 21abaee4-6b39-43af-a101-08de0865b6ff X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?g5A1s9PGVN6gq0Hasw1yvwNxD3pK4D8KzzG29ZqJdL90i3TX7lfm+fHXGi0G?= =?us-ascii?Q?JQhfRpH7U8EGQ7I/F5Re63N4Y+AI9HR5JGp24J6mCD6gq+hyMWhUOkjl/YTJ?= =?us-ascii?Q?FvyKg6FQ8RGOCRg4GKXpzvW8NWbEx4xgKGqmRUerJ+MIX+wNOflO8YnDI69V?= =?us-ascii?Q?lJ5PiBVYbUUrBCTLdTWl4JHBg/6WUB5vOXrKnoiqATw91nndOoPiOHRyQd/u?= =?us-ascii?Q?+OGCBj5U1hMv77k7WHlDuoDC1/niTrwoHUtQoybbKK+h40B+C2pwo+Z9diTQ?= =?us-ascii?Q?ujdCXHBDuiyi967y9R2Ztbj9m/tEVQ5Sob8IvKPyq7Qh9oiWL39Q554kh6HZ?= =?us-ascii?Q?Cx0t3aD7fFtPjaz5Kz+yUStMBNUUIRp36fitBfGs5g/PWLNT8oHbZ5BKEeZ1?= =?us-ascii?Q?Z4kRm6vYcikJMldcFbsMwCWbDkJym3CeG8+G+hnaE0JNP/qK1K/Wq0ZEZ0lp?= =?us-ascii?Q?Juhx6cs078XCXRUHx5ioL6XuREyEFnRhUtlvbSkLM8ugqzaAzIiR5N82khmR?= =?us-ascii?Q?87flaaX/W26q/SVYwa57xNhZdNIvGh+JJo0fubvNZwUGvz+q7dGX5Tpkyw4J?= =?us-ascii?Q?4/+ZwfognunkYJPNtaI1PsqCkwWQilmdf0mAVqQ+LBf9Gupnf3blP3kMvqZW?= =?us-ascii?Q?IpYX5G82j0GaOVT+sLbGqQmyuG/EhNwXh0NCwVxcCw6kRFxRFWyhpkHuE4Kp?= =?us-ascii?Q?vgf0ENOn+6yfvrTeZFVfqyQob9CnRDWZk269MwZc44J29Q7TRfrsMtrQG35c?= =?us-ascii?Q?vwQPHdMtrvLCf+89O+dm257jTUIkh/i0f8bAZPWd6sDitWW6t5Mf75k+oh3b?= =?us-ascii?Q?J/Pgfv0p165pSWE52/naxMLH2pYsXGtWNmdw9ruGDJ7ToS8QBFbhgBofnM+9?= =?us-ascii?Q?K6VDhOSBwcdYVDClmtW9rXsJD1l0jcrt1q3LMuy5JvTfAzyy8aTTzI8L0/jj?= =?us-ascii?Q?Soy4ppfunR5mWRnNzdbldpFxDbiXXv6ZfnIUGeRB9/eau8z5EKUhmdmqktAp?= =?us-ascii?Q?IfioxDoo6Qr33p9lXuJu7djg3xfv6eW08jFtdpsO0sNDkPtigSKrySvQZgAT?= =?us-ascii?Q?G7gaw4HIUfFMZfukJpb2VOkOLo2WhlmMWRzUQeCpSugYhOkbGtIOGQP3zJR5?= =?us-ascii?Q?+IAXM+pjsL8qRaijam5cJnUnfPu3EucyLdicqD46pgvmeG4zkpdluEml4Grv?= =?us-ascii?Q?Kaiw94ClrdWF3bp7R4VGc2wKrMBk+ToHPkT1FUF0unlYCf1SWvwrt+lMD70l?= =?us-ascii?Q?7aiT3AWIDGRThUrNU9G49H/mI09zgXNPOB6xJSgcrgGOf25Dp9IZP71vw630?= =?us-ascii?Q?KYlQtQu/zVTMbqSst6+rmvAEwtoo0SheaiHbBIFt4mLIIeEFo9bvyAH6l39R?= =?us-ascii?Q?hwm3ii5HtoVOzgOZAh8r+Oto4jssUprVoHlBJsSmUWHnvv4Tfq50igD/dZKE?= =?us-ascii?Q?/D+BDiKFmHRnZPa+sS2p9HaEs+TCN/Ee?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(376014)(366016);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?3C90LfTsJAv6BMFOoKIssH2nvK4lNDSzeMsQ5FFEWPdZdWk6pIqBDAX1AuJJ?= =?us-ascii?Q?sBcrUY88YsmAqyLbHy2f7mLbdr2dw2Q2DKtU9VUUD7t1J5UrbDL3JpUoFQzP?= =?us-ascii?Q?r1lBl9ybaTZHYWNe//uANtF6BEmoMpfcuJlqP4RD07MNaoRltyJpQJ9SsGOb?= =?us-ascii?Q?alPIRfGzSTzCgRtmbmmmRxVaWaDuX1WDbRflEjy5CZ9I47G9+MUM8bZUPHf/?= =?us-ascii?Q?Miw1GseZvDZOsClfoE37k2Gizai8iWINraOHnlELKi34WVRgVNJBytgqt5Dp?= =?us-ascii?Q?XGJjRGNxZ5HZIAce3xpd11uc/VmaLcqivScJuQ06+1gEbXGB5nXMPL5i9mTY?= =?us-ascii?Q?loJonLyfuRDQvSDZJyesNE3agdUzpoyKRibbMrCyuqdQIX+M/s+XPM4rSm2p?= =?us-ascii?Q?x3peDAxw5zkiReipCUrOzN3oeeP9aYdO5RPQZ5lJDAux1e72zcU/DQFyV8Cw?= =?us-ascii?Q?m5W0EGyXGnRx2p60uO3MPcH3oN2H5rrk6gXiN6PSlEwVwquthMtoqP/pzpTT?= =?us-ascii?Q?O+Z/WLgdtqXRXAJ6Zca/z5mFfNnufQfyKc8DDFZiAab+Hxtn3Wi5T4zbbuGF?= =?us-ascii?Q?K+GHfJCkfTa8PcqZM0oOFMJcwlycaTnQ2SSmens9l2wSlFBu6QUvqo7dLm6B?= =?us-ascii?Q?liEje2jhaqwgWfaZD5djRvI8wXCdnI9r1JtnwID/lWb7aKA3pAUPKqG/BGJw?= =?us-ascii?Q?kSHAltlquHeD9b5HBu23E+HL9wNimeQtstsBuR4ewAfyBgLly+IfxGqZEW2a?= =?us-ascii?Q?gGtwtknTBC0TeIBWrqGAYCnlkVmG+llB7I2HTzH7zn6q0oZAD07o65AirDg4?= =?us-ascii?Q?GWG9GQQqDOA00d5Go1fqjm8i3ocGvW/0zNQKYAoBbD+5TOZrZdc3g4869KvY?= =?us-ascii?Q?HHBK2OFTJO2IHFfScXmXTm5nX4JbeyjycTT3FqCGfZhlVB4FWnfxBh8Ont0h?= =?us-ascii?Q?q9ZIeTUnuq9QKAxZt8vK4xh903Wpz1Z4dF52MrI3Df0deJsRZH1Mv0YDp4Fe?= =?us-ascii?Q?2wGRCPm3PUvzyWtz2qszvRNlXzDX7BNLDjNfXArsryX0ZiK9UFhX0ThtQyzG?= =?us-ascii?Q?HcPLdjds8KHAHKlHjbwMZyubQg6h9cd60GBcIJEq/tTqNJ9OlFOVMe4EFd6y?= =?us-ascii?Q?8T0xFXmkSfZSD/hZ2+Kg3A3BUTgWGYkR5fMzyjtFBu94hBAN9W1IYllojHhv?= =?us-ascii?Q?4N89E2LtlvkrqGo50DYPiQ2BaVgTpiSw9vvMV1wRvV0mYJlp8lVFO2cnrGwg?= =?us-ascii?Q?z580r7aXlDca4nXftYsaW/xd89N3lX8LCe53mR2YPoL8kFW3owinnqNJjfAZ?= =?us-ascii?Q?bNcpHWdlScFPIIUS4K/yEZkYi/ge5EDlT1u0j9jb+/iAxw0xLlcUYkZ5SS8y?= =?us-ascii?Q?+MPC9sn8pepSuNEznEWLJS0tzTL1lIjPFOmVznVTHGk+qbaAulMLA5b9aXtB?= =?us-ascii?Q?zSkL7vBRpYaie+pnRrswsNZhDEBR9nw9FLpP5Pni8an9h/3IB2rYTcBa3Sav?= =?us-ascii?Q?kUuTdaWqoKPZ4ncC1ODK9zx+88y+LkcQgL2tSHR+oKTCYJYHw+HJ8X240yNe?= =?us-ascii?Q?x5FZlvfyW+Dvsv6U7QCK0gepYPMhL7YZHG8ZACsh?= X-OriginatorOrg: atomlin.com X-MS-Exchange-CrossTenant-Network-Message-Id: 21abaee4-6b39-43af-a101-08de0865b6ff X-MS-Exchange-CrossTenant-AuthSource: CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Oct 2025 01:30:09.0218 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: e6a32402-7d7b-4830-9a2b-76945bbbcb57 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: S9YQ0/3gQ6dW69LMwSskR3X5LwzqCT2Sip+6YaNu0b1H+WrPv/cZwOz/mgrKR+EgqnrEixzliLwDBOjxhM0Pzw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CWLP123MB6259 Content-Type: text/plain; charset="utf-8" Expose the current system-defined list of housekeeping CPUs in a new sysfs file: /sys/devices/system/cpu/housekeeping. This provides userspace performance tuning tools and resource managers with a canonical, reliable method to accurately identify the cores responsible for essential kernel maintenance workloads (RCU, timer callbacks, and unbound workqueues). Currently, tooling must manually calculate the housekeeping set by parsing complex kernel boot parameters (like isolcpus=3D and nohz_full=3D) and system topology, which is prone to error. This dedicated file simplifies the configuration of low-latency workloads. Signed-off-by: Aaron Tomlin --- Documentation/ABI/testing/sysfs-devices-system-cpu | 11 +++++++++++ drivers/base/cpu.c | 14 ++++++++++++++ 2 files changed, 25 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documenta= tion/ABI/testing/sysfs-devices-system-cpu index 8aed6d94c4cd..3a05604c21bf 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -764,6 +764,17 @@ Description: participate in load balancing. These CPUs are set by boot parameter "isolcpus=3D". =20 +What: /sys/devices/system/cpu/housekeeping +Date: Oct 2025 +Contact: Linux kernel mailing list +Description: + (RO) the list of logical CPUs that are designated by the kernel as + "housekeeping". Each CPU are responsible for handling essential + system-wide background tasks, including RCU callbacks, delayed + timer callbacks, and unbound workqueues, minimizing scheduling + jitter on low-latency, isolated CPUs. These CPUs are set when boot + parameter "isolcpus=3Dnohz" or "nohz_full=3D" is specified. + What: /sys/devices/system/cpu/crash_hotplug Date: Aug 2023 Contact: Linux kernel mailing list diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index e3cb47eae982..c6c57b6f61c6 100644 --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -300,6 +300,19 @@ static ssize_t print_cpus_isolated(struct device *dev, } static DEVICE_ATTR(isolated, 0444, print_cpus_isolated, NULL); =20 +static ssize_t housekeeping_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + const struct cpumask *hk_mask; + + hk_mask =3D housekeeping_cpumask(HK_TYPE_KERNEL_NOISE); + + if (housekeeping_enabled(HK_TYPE_KERNEL_NOISE)) + return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(hk_mask)); + return sysfs_emit(buf, "\n"); +} +static DEVICE_ATTR_RO(housekeeping); + #ifdef CONFIG_NO_HZ_FULL static ssize_t nohz_full_show(struct device *dev, struct device_attribute *attr, @@ -509,6 +522,7 @@ static struct attribute *cpu_root_attrs[] =3D { &dev_attr_offline.attr, &dev_attr_enabled.attr, &dev_attr_isolated.attr, + &dev_attr_housekeeping.attr, #ifdef CONFIG_NO_HZ_FULL &dev_attr_nohz_full.attr, #endif --=20 2.49.0