From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from BN8PR05CU002.outbound.protection.outlook.com (mail-eastus2azon11011047.outbound.protection.outlook.com [52.101.57.47]) (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 CD794238166 for ; Wed, 29 Jul 2026 14:25:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.57.47 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785335156; cv=fail; b=NryvYF6ykPZ32bWiwnc2eBXXM3b3EC7KeEU19mwPC0CmNItYKUZGyfYuBL+UPOyT5/3+xs6ZtKK7E+NqwKGaV5s3AtWC/sgre8nI7116s84ildU4ElqBlTOOQpuptrEA1i7o2p3u7FnY+XZuy0iMx2xCygsfErImxSrqNUw6EYY= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785335156; c=relaxed/simple; bh=xB2M2npGSxUqwEKuX+B6dl5/2iYBVRyYL7v2cwvvRFc=; h=Date:From:To:Cc:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:MIME-Version; b=ip8ULF22J9EBJ+C2o2S4imzlGi0wUVAyf/NmVxgx/2/8fEssewcwDrqYIceQel/aK9+zgFXlB9Sbc1XUuVrYv4M7Sy1sLm6odtAUmYdBMteoMXvd+PG6Lc2ctLJlxXcjj7RYuTaNfHB+geAE/TN9wOShol1zD4+1PyCOhrpPC1Q= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=NEOrbH1n; arc=fail smtp.client-ip=52.101.57.47 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="NEOrbH1n" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=P+EGLkHHIyjdK2ZvlQBuLKZIW0uchffCHmypIflPiKf8SfYprZM3SYCvT8lFWVh2pJ8qzJFwgK0YUz0mkRXUXrfpfuLOG/10AwuVaHIGKtXHE+PujWsjBc/tj0aXOABt1QBzCCnn2w1BXRYLKK2dTZ3ocVNAI1lz+9qgPixICtrAZYK5Ts7+QloQWHo2K9QoVlwwwJZphxN1Ks9T76LM7MzIb6qtRcZROFCPs7fPa0WCb/iWGXHyfe75aS+szfWLxIPDhnR6y8fNlFd5KFRXOtrMKSW+mzLhQ5VouCeyWrEZCGAhGaNkNLcaiYNXlEFr2KePigw02CZza1Z4x/IcAA== 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=o3FHE324qoGqVnWSPAY64MjMNlIgx3lKKZpFvlpoffw=; b=n555kBok68m63ZoWFxzglvjBOcY0VTzX58mQORh1UNoPnBhZXjaScW33avQgtimaTfn+3Rnc5VCC1oWF1/jzELvcsiAL1Xi0l06KDvql+gcxV9AZ2Eg3FGErQrfXpUi4TbkDKydqQqOuZfoxp/6wBzTKP7z3uZX6XGpQedYuxMJeKOQg5pyP0V6Qy/MxoJmis/A/LNUHUVJxmXozDP8vaPAndCcJL98ES8ccbXpuCob+zWmAaDRP5yoizZK0inhDGrRIG3EQhpP+LPxVZbBrrfMOrCaCudsZLfOuhJH+glGB53F0uXb4V+uhNku+U9RpGqsRoeM3Xy2y1AUFQ00zPQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=o3FHE324qoGqVnWSPAY64MjMNlIgx3lKKZpFvlpoffw=; b=NEOrbH1nhEgu0M9yKREitqCnd9Dw6H0SQHkVnUMP2ixQQltgIallSSg3rhCVG0k8n97Gc5dsFn0fgV5pwm7M+hMpuGcd5qWCbAJNVN4vDTJo+wc1PR4W7m6RGkN7st79/vxBRhbaaooYyaZhAXNO/dZYwvdXs4fL3g8YkIpBnpaY7XeH29PBWNlPqCdYiM3xE2pXLFxg/GKhsWosLFwrmkqJeknsHfmDeBdD4leLZl7xwRdKIkJFsXrCAwMFg9wsT+pqNBZWuiGha8WL12qeeksce9rvqg+q3JnuKuMv4SJrHCGlBaeeupgYcZ23DUZwRR1OYXzoDDX4pDXdHlNE4Q== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from CH2PR12MB4824.namprd12.prod.outlook.com (2603:10b6:610:b::22) by CY8PR12MB8241.namprd12.prod.outlook.com (2603:10b6:930:76::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.270.12; Wed, 29 Jul 2026 14:25:49 +0000 Received: from CH2PR12MB4824.namprd12.prod.outlook.com ([fe80::34d6:fda7:9290:35a9]) by CH2PR12MB4824.namprd12.prod.outlook.com ([fe80::34d6:fda7:9290:35a9%3]) with mapi id 15.21.0245.012; Wed, 29 Jul 2026 14:25:49 +0000 Date: Wed, 29 Jul 2026 16:25:33 +0200 From: Andrea Righi To: K Prateek Nayak Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Christian Loehle , Shrikanth Hegde , Phil Auld , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched/fair: Prefer fully idle cores for NOHZ balancing Message-ID: References: <20260728214442.1648483-1-arighi@nvidia.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: ZR2P278CA0028.CHEP278.PROD.OUTLOOK.COM (2603:10a6:910:46::8) To CH2PR12MB4824.namprd12.prod.outlook.com (2603:10b6:610:b::22) 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: CH2PR12MB4824:EE_|CY8PR12MB8241:EE_ X-MS-Office365-Filtering-Correlation-Id: 74eb5be0-4fb0-41d8-7a97-08deed7d4901 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014|23010399003|4143699003|10067099003|56012099006|11063799006|22082099003|18002099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH2PR12MB4824.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(7416014)(376014)(23010399003)(4143699003)(10067099003)(56012099006)(11063799006)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?PwJEsmZFmktj6kXsJ3CMlJqFAa/QYImPqOBZKsT8mydxlSn+W+5l33c7U3wn?= =?us-ascii?Q?tcyCvHINM/7Z9/gKLEXkp9s89fH53IYgaEMxiPQ+7kiWuwT2wjcKAncWuLW1?= =?us-ascii?Q?WEpjBULhGjL7VyJKZhIb10yrVBk4/iKtTJ/DZzgamcP+g021ZF5JPbOVb1NQ?= =?us-ascii?Q?+S9JuE52XlvzViP38rMUbP+EDhTjVJ6xUXiPqLp+q+STF+hFuDvvU4MdtHdi?= =?us-ascii?Q?7Z5zmSKDKAcAXRhEhvDyd5IrqZxtNXdNGbmXVHbvgQDb/ev1Nr0FJt5dyEMG?= =?us-ascii?Q?9qQP7GwlcOmiKAUbqENMc4PlY+hjFEDYiFy5gwbfIWb//HHkt6X2ET36f7iV?= =?us-ascii?Q?yIQKOvIt/g1ob7Psv2WO11VFrD9IZnsKTat+tUWGVhkAa5t163rvDiUFZIHS?= =?us-ascii?Q?O056H9PsawRHxp9Fq8aiWwe9Tp+0bbe22k+4u5rqxizI3mxF/pWllCnZTMzb?= =?us-ascii?Q?UKzkmp5pSkRdXxOMy13CgeMPdlEenAAJlMX3nAPhOukvYeCOLqnaH/c4e710?= =?us-ascii?Q?sVdm2LD5+fDSKHYnUh9DIFVUzImVzTGpYZK4UdJeJSnJ26/24aywxQFyfTA1?= =?us-ascii?Q?TWwKI9cVQi8ZZI5t+MCPjWsLwPQifpJsJw+CKcX/WBGRiuHfypUJnduPtIVv?= =?us-ascii?Q?IN4lBnqoznUNyzzQWBPISdgM8IJzOLUYNGLI5otR8qQlQXftbhb4xfKksDow?= =?us-ascii?Q?DxtvUiKx+XVAODc5C2cJB7zaOOt/Hp3YzAII/AobC32w1WHnIcPALm2C5AYg?= =?us-ascii?Q?hp8nyIcpzXzypdSX6xI6IN+9uN6tjGTrhdWClCfEgs3mLRCUsapYXXhhUwG7?= =?us-ascii?Q?GRYV69VTXT/47YzjIzhuLJFP4RskV8iW+RmFY0vUaTd5Au/BbOdI/cL/P7Y3?= =?us-ascii?Q?3S4RrL80h0cQp9Lr6cRIZ6qyldgtURiv/IuOhcsrfYFeAqSYB2sFztbN6VBW?= =?us-ascii?Q?ipMHkd5ONR+naLoRMjEGwqFMkbfLhapeYlNvO1VGB9QltTea77Q1eNYD9EHv?= =?us-ascii?Q?MpeziS8BJ1ACrMZb2fcGvWqoBbQrLqNaeyWFaU/OBGO/fqvuLBOKq6KWF+Vk?= =?us-ascii?Q?yLDXo+pzlRLR3uZJaDubyqGjLutQYZ4droLaLreaiG775topFshbqEhzmDmK?= =?us-ascii?Q?w42sCaMnSsxDaQ7HHdnJjrB47k/OI/04ArWuSqmn9yQ5aD28lO8WL/QrF9oB?= =?us-ascii?Q?0nFHQ/dr274Cy9umCcLRoJa9qv/HUFMdMyCRfsPKF43BJcul70B9xEoq9Uya?= =?us-ascii?Q?2UDuVfR/1QblV6yedUOJp5zVk6JK6P396aehDXaEb/uFA+mgnVIdwHtlod0x?= =?us-ascii?Q?hUmSZx4W6GnSwq8WO9C3SP8pQJ7fku9uD9oRK2l4+GmqLJ2ZxT7Jc73zmjUa?= =?us-ascii?Q?agFf61rBI1HLGLTxyvKJdKEgxMlpyXFQ2ZSuKCYvreWAXcafDfrCNBRi8AVz?= =?us-ascii?Q?1W+SkMUavF8WFK8esrXDsMKSflxlUJI/WRJ4h4lR+pe1rPRSewHY2+Td/3FG?= =?us-ascii?Q?ThHIqEl6eY26IrML485PgYm15BZnnvECutRk0DAHhONcl+AxMBq2ZKBNvfFc?= =?us-ascii?Q?V16Ng9HjeZt2rvwzFjxVFLkreIM29bxbMDc9cYiyYtw80S1/wp281z3o6wJb?= =?us-ascii?Q?Uo3YqWjy+8sHn+ISJAbfIDsJtFmgIbVeipkiLXNKsB0l8ZJ6vD7VsqeQyR/H?= =?us-ascii?Q?jbucliSrl2CgF/6aq5ktbpn8NkVuq6hIsorfYEUOYku5li8rghb8QkH0Q7/C?= =?us-ascii?Q?3QqWbyK2FQ=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 74eb5be0-4fb0-41d8-7a97-08deed7d4901 X-MS-Exchange-CrossTenant-AuthSource: CH2PR12MB4824.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Jul 2026 14:25:48.6965 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: PCILeWDtl7kEMnLinVRW4NxMaL9S3ERI3HlaKIfbnthh13liSTzo9WzWhG8J/OtE5OCO25uM2y0Bi40aFbCMeQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR12MB8241 On Wed, Jul 29, 2026 at 04:09:05PM +0530, K Prateek Nayak wrote: ... > >> It is safe to use "select_rq_mask" here since this is the tick handler > >> trying to find an ilb_cpu and "select_rq_mask" is only used in contexts > >> with IRQs disabled. It can probably be renamed to suggest that it is > >> safe to be used in any IRQ disabled context as a temporary mask. > >> > >> Thoughts? > > > > Agreed. We can also add lockdep_assert_irqs_disabled() to find_new_ilb() to > > better document and verify the condition that makes reusing select_rq_mask safe. > > That works too but it just looks a bot odd to have the selectrq_mask in > a load balancing function. Ack. > > > > > Speaking of that, instead of renaming it, would it be better to provide a helper > > to access select_rq_mask with lockdep_assert_irqs_disabled()? > > I'll defer to Peter on that :-) > > He had previously suggested renaming it when there were discussions to > reuse it here > https://lore.kernel.org/lkml/20260320114312.GB3558198@noisy.programming.kicks-ass.net/ Thanks for the pointer! Looking at that discussion, this seems broader than a simple mechanical rename and it doesn't appear to have converged on a concrete interface. It looks like a useful but independent scheduler cleanup and I'd prefer not to make it a prerequisite for this. Maybe for v2 I can keep the existing select_rq_mask, add lockdep_assert_irqs_disabled() and implement your suggestion. Results are looking good so far on my side with your change. Peter, do you have a preference on whether the mask renaming/accessor work should be addressed separately, or included as a preparatory patch for this? Thanks, -Andrea