From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from CH4PR04CU002.outbound.protection.outlook.com (mail-northcentralusazon11013022.outbound.protection.outlook.com [40.107.201.22]) (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 118C7305E10; Thu, 7 May 2026 18:59:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.201.22 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778180385; cv=fail; b=W6pzgT6TIInHoD0Ruu+vLyX5B/4D592C0WdlD5uH61MAmwa+FdjBTltTpGX88k3C3q3ze4YnCMPt7pej697ch2MAD0WNbaMt5o2OQhZo4hk2xndN7LNqckyV0butg1LR3rm12RZmZraNBlbJlYOnUFp9GYDouXfS7LBtkX4zxLU= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778180385; c=relaxed/simple; bh=9QzdJNI0QRaAoRaxX4cBbYO6IRSuSWUaRI7jNNfSGuQ=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=ehlo4W2aXnnD4C1UBQNRZjvTRE0pvnk6loU8Zy8MXLHhgRWVG9Ib1dw0UXce2+J2ClzgYwyPNjmZ47lwj2Uz/8AAiYZ/id1X+Z4zrZa6Phc0S2Agi5j7MXx1rIqTDzICf8xLTdxEfdyuqTQDoF6jlpmdfvZbXqk49M9tKSjCtQY= 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=djDF5wzF; arc=fail smtp.client-ip=40.107.201.22 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="djDF5wzF" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=ZnGlSRIx/uN+DCBfojf0olYShr90RHlreYZW4L7nbTesQPdHZYF+RGOT2SbeGzgbI8klsXIyW0gFzsOmz1jpbd+dKTCxwadd0XbYYtHMNBDcj5nZAClnzkBgf0fLXq/ZlwYZiE4cJ9m27Cs54wBqy/DiDWfV8l/oDBu0sKsTqtGFEThnYYKB9UvkpUZquuLbAU3lGrIs8ruGZqNbqKvbP5KUXHccE+zq2ptWyXz2zHjuxPPptftcfgt5Pqxaeogyo+LXH+pDsM1uOdKwzjTEgmGb6qPiyrHJnJZ04/8nnrbCKLBTgbpMfj/4bAjCpbaveWzczDn7imAxW3P6Sny70Q== 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=JhOcJMuOPIRvcF8OSeGhh/YoFBpY6QNdDaC4Mq+b/XY=; b=rlwI4SF63iqM93Q74/td7uEZu3SXD5fOF0J8SA4JjWyKTFtueuBbYWcFr+9rH5qy0zV1ufIt7DakMMz9x6Wh6gskNF2XN/3KKyZ5ymMNkEtbfQ/q2ftLr2zAVYFZ2lmEDipMFLC3QD5Lyi87YnEeas2GGqPy0tuBcqGnwPbiXYOwwWVhcLQT06sXE6Eeyu/Vxp1EYbuCZOyaLb09gsb/LVlrV+HEAw3ldr5eWnZ6BvtZSQqJKglHq9CMjD36qS/EIE3WlP0FRwPGCT5zmPtLv63/LUG+Cr5MGdSyfo2f0ytTcm4ra8XfK0w2E1pKrIR5zC4aeFymxJrSAwe4cxO7Ng== 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=JhOcJMuOPIRvcF8OSeGhh/YoFBpY6QNdDaC4Mq+b/XY=; b=djDF5wzFEmAs+yizKIT0dnn9RnlXIhETziPJckuj5v4Pso/5VMK8hJaNXw3EFRokSBRjRlUqNkEaxNqG3xLC0Ywt2iyf5gfo7jwdIAokJCWvFggWU9myd8t+IuA4nro9hkzAKK3kD6pn+5+p32CcadS1sIUXM2+/kF5eLrT+lGyz9td9cpHFdA1QOgUXdZZV2D3KAQasFx59EIZmgNaJmpxtPVL2qmKcodM1jHpu9JDu5o3OIoJBI2zL0b4Gw88VFEvLenr04xnRAYGSbzw+GlouYIM2RTwdARPiAxI7bf4BShyvok4a4pM9mJlG0bbAe6IoDwMd3xQO0Irf0aclEQ== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from DS0PR12MB6486.namprd12.prod.outlook.com (2603:10b6:8:c5::21) by DS0PR12MB7994.namprd12.prod.outlook.com (2603:10b6:8:149::19) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9891.15; Thu, 7 May 2026 18:59:37 +0000 Received: from DS0PR12MB6486.namprd12.prod.outlook.com ([fe80::88a9:f314:c95f:8b33]) by DS0PR12MB6486.namprd12.prod.outlook.com ([fe80::88a9:f314:c95f:8b33%6]) with mapi id 15.20.9891.008; Thu, 7 May 2026 18:59:37 +0000 Message-ID: Date: Thu, 7 May 2026 14:59:33 -0400 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 0/2] rcu: Add debugfs interface for pending callback monitoring To: Gustavo Luiz Duarte , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Boqun Feng , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Vlastimil Babka , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Breno Leitao Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260507-rcu-pending-cbs-stats-v1-0-8f4eb3553bc9@gmail.com> Content-Language: en-US From: Joel Fernandes In-Reply-To: <20260507-rcu-pending-cbs-stats-v1-0-8f4eb3553bc9@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BN9PR03CA0198.namprd03.prod.outlook.com (2603:10b6:408:f9::23) To DS0PR12MB6486.namprd12.prod.outlook.com (2603:10b6:8:c5::21) 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: DS0PR12MB6486:EE_|DS0PR12MB7994:EE_ X-MS-Office365-Filtering-Correlation-Id: 248dae49-6d58-4969-6021-08deac6ac93a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|10070799003|366016|22082099003|56012099003|18002099003|921020|3023799003; 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:DS0PR12MB6486.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(376014)(7416014)(10070799003)(366016)(22082099003)(56012099003)(18002099003)(921020)(3023799003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 2 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?NkFxU05mTVFEZ2crRnVYQytoUVZzRWtVa2tiMHlXQ3oxVkhPTFIvZ3RhdTJr?= =?utf-8?B?REtKaHRlMnBSMGlOZE4wQWIrOHJvSGxGcWpqRm1iWW1rSWV4RXJ2bXdLM1gr?= =?utf-8?B?SURnaXlNYnNSZ0JUaEZqRTBNd1dFcVdQZjJaUkxaNGZOZGVtTTNzWWhZVFVu?= =?utf-8?B?R20valFlWlI0dFJsNHJXQkZDTXM2aG80T1ovZWNGNGpOY2taMGU5b0dCYTUz?= =?utf-8?B?dGowbzZ2Tm51dkV4ZEI4ajRiRUZEYmRicGk2TWpsNVhFek8wTy9uOCsxd3RF?= =?utf-8?B?WXd2ckI1UUNIZ1l6MUJweW9SbWxSWWtZSEYwdHBjajlZVjhNMlB5NGZ4KzI0?= =?utf-8?B?TVRHSEZPb3NQNVAwcytFTFdJUThablg2Ukd0YlNNUXdVNFVPRmRTaHNabHAw?= =?utf-8?B?UlFCK0hkbG1OL3I5dXgzS3NMNCtlaDZlMmdkYmlJcm9xMS9JdTkrd1ZXSFp5?= =?utf-8?B?R0F0Sk5aYlNteVZxMzZNR3hOYmFVYzZ3eHU2OXdVdDFhUTVCTzh2SUJPalRZ?= =?utf-8?B?ckJZMWpQRFJuUVhQWVhqZUVCZXBYQXc5T3VoTEx6bWt2dS8ralpBNVU2V1hY?= =?utf-8?B?TjNicnRxUUZHU3hpN3J5Y1NEZnFEeWFWRTgvbHp2R0UyVDZRUXRQYzhzcFF4?= =?utf-8?B?MXFLK2pzMTRjYStNTnZoVzdEWWgrR0h5eDhGeXRra3VqdWtkYzJOY3FKSlRS?= =?utf-8?B?eTlWU3VUcHRiMnVMU3RJSDBqK25HQTRINzIzbXc2Zi8xKzZzUFNLSFp2SFpZ?= =?utf-8?B?UWI4K2V5aHR6eDRIZytxTUVrMEhuaXdieXZiNkpUZTZ3dnpkbEVsbStiTEQw?= =?utf-8?B?SVJhbkVVYVNPTW9XeEtBbUtUZDVxem50cE9ueWtneXFtZmE1OENscmxhUEhw?= =?utf-8?B?a3c4YnZTYU5BSDkrNkxWaWxta1hvT1JsZVVsVnFvTktQNCtNdytaL3ZXS1pJ?= =?utf-8?B?Zmx0dVhjV2U2STJzMTNjQktBbjcrWkxZWHB0dERqcnNVamt3SkxJU2xPZFl0?= =?utf-8?B?dmZsSWs0NGp6MXJ5OTNOeGl6L0hRV2hxQ3g0SlNVYzRlTXVyT1d4QVR6WEVO?= =?utf-8?B?SU85eXhXMWdxcE9ZeEpaWnBuckNmVjJobHZiY1F3bWloZ253c25EQTkrWmtB?= =?utf-8?B?M0Q5a3BlbW5HRjBoeGhoVHVwV25PREF1YlZLMGptR3hodXlJbVZQRHBDUkNm?= =?utf-8?B?R1ZlNnlpSUc0c0RZVW1ROGEzWm9EUldYSFpjRmxIdzZ2d3pyU294aitzZXli?= =?utf-8?B?WWpxak5YSkJkTHo0Q2IwQ2lRUG5teWFEVmZDVmk3QVAwa0RwZWR6U0R2dFZ0?= =?utf-8?B?eUJla3ZtSVdBazdzcWlCWC85c0JQUVU1RDZyT2w1NzBMekY5ZGV2VHRjUWR0?= =?utf-8?B?bmc0TEQwa3hpZWNVQXRuUjE1aDQzUUdldW1jUzdCTjQvZ3J6MitiaDdxMmRZ?= =?utf-8?B?MkZOeXkvMlA2MEplK1pKd3FNQUFiZGxjOWlmUDBDVmh5K1pEU0VaQnB3T2Rn?= =?utf-8?B?amc3SFFsSE8rQ01vOE9tR2FLeVlDbWFENHc3bFdSbUMwZTlsNmFHeEl3VVpQ?= =?utf-8?B?bTQ5S3ZadzNicCtyU05kd2RsYXZreW9US2NaUmh6UWZGUFRXVG9mYjFBdVpH?= =?utf-8?B?WlZmemJTSExPbmVSZkRpMHNraERWbzJFR2pmc2JZNUJqdmNOWkFXeEE1azhY?= =?utf-8?B?TDJ4dlpvbyt1Tm1kMFBDMytTeHRLcnJGSEpvb2dDblBnd0VUeTNuSktaNU9F?= =?utf-8?B?TE1vdHE0aWh2QWtlNXBuMi9LU3JQdXpUaGh4M2ZadzVGSW1DUWt5aDFCM2Zu?= =?utf-8?B?a0UzSmdVRlVSY2t0MzZqL2U5SEg3eURxVDZlZkZiQnZJazBOalRJTk9OcHVp?= =?utf-8?B?UzRSQ09xMDFNak5IYlVwZDBlak5GcVpvRFlmZGNEVG9MSkFzS3hKbDBoZ1Fa?= =?utf-8?B?QWVkdHFwT1c2NjUzWVlROFVuZWlDend3QWd1WkFyZG9Sd1BNenUxOTJzR05i?= =?utf-8?B?anlVZEh0NnMzcFpHOU8rNHJnMmdOWDhrOWt5aEZhR0JkRHVpeEVjdGFFK1ZF?= =?utf-8?B?Smw2Y1F5TllJMmJEeWxIcVY1WWpDbytVZ0F5enBTZC94d3AzWFJvYmRmakpH?= =?utf-8?B?RG5VYnhYYk1iakc4UDBrQnkwQmcvR1huaThJbmRHd3hKUDJVTXNucUxtRVRa?= =?utf-8?B?d0k4RWtyZzVDeVpDMEFOVUt6cWxwZFNiUTU4bUZDdDN2UnhDYk9XVGk0UnZO?= =?utf-8?B?QXFid0xjN2h6WjR5YnNPV1A3UEVoY1VBN2hCTGRUTlQxa0UzVVdESGpxVTlr?= =?utf-8?B?TGhZT2g5Y0RxNlhUVWtPdmhOeC90NEx2d3FtMUtheWxUMEFGT1JaSTk3SmtR?= =?utf-8?Q?g03yKhQhz7CvG70h0Y7SphS3z+VuyRgV9KQRyixZFXoLu?= X-MS-Exchange-AntiSpam-MessageData-1: WfQ618Y/AqdeJQ== X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 248dae49-6d58-4969-6021-08deac6ac93a X-MS-Exchange-CrossTenant-AuthSource: DS0PR12MB6486.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 May 2026 18:59:37.7381 (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: RDRX7kSDwMGPT2fj/sef5Xb7xb4tY4C5W/UuWy6kGfIk9evK84VNpgthLnbPrq0Nu2/AT3mU03vhXqBhERlx+A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB7994 On 5/7/2026 1:37 PM, Gustavo Luiz Duarte wrote: > There is currently no easy way to monitor how many RCU callbacks are > pending system-wide. The existing trace points provide per-event data > but require active tracing, which makes them awkward for fleet-wide > monitoring. Knowing the depth and stage of pending callbacks helps > admins reason about RCU health, gives an indirect signal of memory > held back by RCU, and is useful when tuning RCU parameters. > > This series adds a debugfs file at: > > /sys/kernel/debug/rcu/pending_cbs > > that reports per-CPU pending callback counts with a "total" row. > > Patch 1 introduces the file with per-CPU columns for each segcblist > segment (done, wait, next_ready, next) plus a "lazy" column. > > Patch 2 extends the file with a "kfree_rcu" column reporting objects > queued in the batched kfree_rcu()/kvfree_rcu() path > (CONFIG_KVFREE_RCU_BATCHED), which has its own per-CPU queues outside > the main segmented callback list. > > Signed-off-by: Gustavo Luiz Duarte You actually don't need debugfs for this. You can just use bpftrace and instrument trace_rcu_ (with other RCU tracing Kconfig options enabled?). I had something like that working sometime ago. Generally RCU doesn't add userspace interfaces randomly like that. I remember Paul ripped similar things out some time ago.