From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-00069f02.pphosted.com (mx0b-00069f02.pphosted.com [205.220.177.32]) (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 818F91E1037 for ; Wed, 9 Oct 2024 19:07:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=205.220.177.32 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728500823; cv=fail; b=dSIYdWqZm/6nfJShSyZbcJmUYCyJX/FBUKL8Igmc2qYT562jfY9fbiEAyxgxGahr605LkJp3Gb+fhNMf3GniBw6+tOppae/Eq0sjxICoiPtrbntihlmWTaRuzvdFlHE9nX0XyiC3xoxs7oqxVBifcZ+xxHQUnX4dCUvINw77iGQ= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728500823; c=relaxed/simple; bh=Efqkr8WPRqYu/tMWfS3qEfuy1inL5fnWC9c5IMOmgzY=; h=References:From:To:Cc:Subject:In-reply-to:Date:Message-ID: Content-Type:MIME-Version; b=f4tY7u1bDSkzEvKMwfQebs5fBCyuGYx2R7dLzGi1JDHv+1HGNSGnSPhBmlbZ/8mTiaRCtAOryYs+ah8CG3daCN1ycn65R9/95c3LtGUswRZC1KRd49GRTGpmLr2tWHw8ZyIk58eKpw8Ys3UUGFeDTrIO0BUdqFzDWuauRcxJYNM= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com; spf=pass smtp.mailfrom=oracle.com; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b=GjHJQMPJ; dkim=pass (1024-bit key) header.d=oracle.onmicrosoft.com header.i=@oracle.onmicrosoft.com header.b=aRRyPRUw; arc=fail smtp.client-ip=205.220.177.32 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=oracle.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="GjHJQMPJ"; dkim=pass (1024-bit key) header.d=oracle.onmicrosoft.com header.i=@oracle.onmicrosoft.com header.b="aRRyPRUw" Received: from pps.filterd (m0246632.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.18.1.2/8.18.1.2) with ESMTP id 499IIQT2023392; Wed, 9 Oct 2024 19:05:59 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=cc :content-type:date:from:in-reply-to:message-id:mime-version :references:subject:to; s=corp-2023-11-20; bh=TiWNKCDPbAar2Z6KTc KdUqS+CDqssjXVyvP6yp584kI=; b=GjHJQMPJSUrm7kxGN4vxFJM4DbZQGb+ImQ Mu4ZdFX4x+YUnNss8PrmnB16u6yyGsOTW+rse1r5C/cc1wl2LznA1x17P7QRf02F OjgFbAPLMd2TnN5b1DZpdlgEYtMn11g7ItEmZegC7hxqga2BwfyMSytCXeNhELwb CL3me48W483A+u+QP0vcYDqUvHnLDK8YKZpk9NSnsi3JQAToe8+ZYYy8T2x5JjU4 oWmLRNUpF1r0RDgJfQdrIooyKIXa+5rQc9zmBUpBqj6jLXXgLRApTT/Ej9KnK1ve wAfEHIOq0+fI+TgO1gbXvp3yNaYKa6dd4l+cBKzPfv+Iz65SUPFw== Received: from phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta01.appoci.oracle.com [138.1.114.2]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 422yyv96nx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 09 Oct 2024 19:05:58 +0000 (GMT) Received: from pps.filterd (phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (8.18.1.2/8.18.1.2) with ESMTP id 499HQREY015234; Wed, 9 Oct 2024 19:05:57 GMT Received: from nam11-dm6-obe.outbound.protection.outlook.com (mail-dm6nam11lp2176.outbound.protection.outlook.com [104.47.57.176]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTPS id 422uw926tu-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 09 Oct 2024 19:05:57 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=R8j7npMkTE91w4iC3qWp5Lr9Q0IAPaonM03EI5L5cVjCteoB3FNarmLQ3parWWtMa8OpoflbhyHRXg/6ywH+e2yOQBof9Wv9iSwuj8AzcgsHJ+9F+UrfBm79zISkxP6X8qXGsYf2iqOp614dsEaOZ86Ef7VhvVhfrOxlW3Cyigcj43jwk2x4vhUS4Oph+GrPnonj1fZ6YNxZxfvTdYyRpE/C1uwCSfAf9UUNwS5khrUUNqTM1zs+/0xTbkZCGp0+qMqHLb8CHMmG3D45HQ4qXCm1k7Y0w3ZaU4o/ANFIMF4YGefjMa9n1RcIMYi+w2wK9bOQpuYJ+rSGAbdacrXz2w== 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=TiWNKCDPbAar2Z6KTcKdUqS+CDqssjXVyvP6yp584kI=; b=jVDrjm7p9U4bEgslJnpIzqDT09HlfGoT//lUea3qT2aKIUBDCY/FixUhSmRcXdM0WWGwZX2/a5aZMtypiKUrrjjj7N/dsjcAiKTyRuuuCKpaJpvuWotuzNzsrHPUxM7irxkYkX1E1ojQadsPsIjWbZJ05O/pWhzZ8OK6rGjEZFRGe2TEfOhgZlK7dyaKPJFG2BzlCuGLF6IS5G1gx37cNZMDq9RIvYR8zHIJGt/TdSNnKkN4MScs09WxhEp80e9TWgv6nadRowsX1H+z8ZZj52Vow5brSHk91gZkHM5TkaZO6yd04/P7nFVD3J71ZPIZq/xZBW/KsFVubCIh40KEow== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=oracle.com; dmarc=pass action=none header.from=oracle.com; dkim=pass header.d=oracle.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.onmicrosoft.com; s=selector2-oracle-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=TiWNKCDPbAar2Z6KTcKdUqS+CDqssjXVyvP6yp584kI=; b=aRRyPRUwmPMpWXAx+7kFoxuFHTU4A2nxNAeEQzFxNqQrfhAnCgy0bCVVyh6h78XM4WSQFJHgpnWHDX9pOCGejY7FtEDce7FzjWONRspYSo/sUFn01SRU4wrQLgcgwE9+U0jOHwCzEk7zucGqdAqpVKVX40MH0wd8Uk+YQpnbzQc= Received: from CO6PR10MB5409.namprd10.prod.outlook.com (2603:10b6:5:357::14) by CY8PR10MB6514.namprd10.prod.outlook.com (2603:10b6:930:5e::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8026.23; Wed, 9 Oct 2024 19:05:51 +0000 Received: from CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::25a9:32c2:a7b0:de9e]) by CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::25a9:32c2:a7b0:de9e%4]) with mapi id 15.20.8026.020; Wed, 9 Oct 2024 19:05:51 +0000 References: <20241009165411.3426937-1-ankur.a.arora@oracle.com> <20241009165411.3426937-5-ankur.a.arora@oracle.com> User-agent: mu4e 1.4.10; emacs 27.2 From: Ankur Arora To: Ankur Arora Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de, paulmck@kernel.org, mingo@kernel.org, bigeasy@linutronix.de, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, frederic@kernel.org, efault@gmx.de Subject: Re: [PATCH 4/7] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y In-reply-to: <20241009165411.3426937-5-ankur.a.arora@oracle.com> Date: Wed, 09 Oct 2024 12:05:47 -0700 Message-ID: <87o73t9jw4.fsf@oracle.com> Content-Type: text/plain X-ClientProxiedBy: MW4P221CA0014.NAMP221.PROD.OUTLOOK.COM (2603:10b6:303:8b::19) To CO6PR10MB5409.namprd10.prod.outlook.com (2603:10b6:5:357::14) 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: CO6PR10MB5409:EE_|CY8PR10MB6514:EE_ X-MS-Office365-Filtering-Correlation-Id: 13bcf6b9-0ebe-4829-3b9c-08dce895644a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?GfSaVbXO8ndk1udw8WITzpuEiatxNCzWzloip7Yma/O3S9F+8KLQq8nGA4nx?= =?us-ascii?Q?DYkskRGNUZ1cQghbGp1NUSw8j26WSL7qKZUQETIW2K99E+ZPZZj6woog6ZsS?= =?us-ascii?Q?g/sXYJXcehxZYsn74pfLnhQYTX6ESHaVw4pJaCS+At3ael5/quY0mt6YfJaN?= =?us-ascii?Q?+OvAMb6P3SYjdDZaKEXVs+gbNvyNh4Y/RnwhJTZMBndCly7t9zrFJY/4zdxg?= =?us-ascii?Q?wrq7sow4pXgkgY55wibf9sVPno7nj+8f00LY90cngsZf4a4g3P3PidstHspV?= =?us-ascii?Q?zEEw6qDdb4zgkfd1R9Lggkq3fidSPDUzBP89QMSOKHytqcvH0lpfkJn8u/iR?= =?us-ascii?Q?JZq174XZRoeW2cCGpmDzbOUy2lVVa0SsnMJF2Y+od1twrDSTkzd/wmmUvlUL?= =?us-ascii?Q?8saOQxdpdSDf+AXNIWkw20M08uJ1FfEtBT+6TLHcfY099owo9khM/hVAlLQa?= =?us-ascii?Q?9AZqfz3yY+EAGrpHvXv48ORB+iEgIeccZV2ey3wLSexY6pmZGOzGxaa7ofAy?= =?us-ascii?Q?LsmNKFIgHUx+6Kd4UBkpMZkjaM9GleURNg1BIwfkByKG82QUrhKKy3AgvE0U?= =?us-ascii?Q?limECsXglJKd2urMeMrmVMEy2SNmzeOklYyGc2j+O9/aCtBWophBi+HVbXLF?= =?us-ascii?Q?7OnVl/Sa1ML8tRnTOpqT5FQudI+oYoz/BkkxFv2B+dt2FiFkC2owOwxZy9xE?= =?us-ascii?Q?yfDwMHmN4Mdu/c3ABWy+rUyvIikvwoq/7bHFHZnzPT3wuX2mYwNkQbMYd+Vy?= =?us-ascii?Q?Bp7UQnxb86NgJPvuB3hoDyln+6OwQ4+LKhA9FhvTLt7eOIHp9cegU7Z5w/qU?= =?us-ascii?Q?2xb/Dx+QWV9E0Ams+X88Ni/ZgMg0qiXOtWXEYIEaPZo+qHO/w4A0j8Nmbpa3?= =?us-ascii?Q?E3coB1RJMpfgflAltBREoLyRfw7HwQdLCd22Rnw8wU4gLvhOX3s2vlLkMaaQ?= =?us-ascii?Q?nSb3D7nskFx3vtPz6ZFInkq5HVAFxGLIu+bfy9UOWassb7L75LCvpx05GfaR?= =?us-ascii?Q?t3ei3/yx40iKjn+sHGAMaV+E7oEM6Y+1FPnuEuYLsHl9WXFTmd+9Ea/O8p8C?= =?us-ascii?Q?IMtgl+5eiNjslM0v0T+R9t2xMZriBi8hC1E5zHisLeZuuQ+K/lNMY5Oyr4ZI?= =?us-ascii?Q?630Ry4h2Ls3GmFi+me/xXyXh8kYBW5cPC4GHHbmZJ9Oz+d9Cixak8DBzHByX?= =?us-ascii?Q?8t4o4Mf+PK0Sb0sAaFhe9v+Oc/PWjAnSfDP9gbA1J90Oos2J4KOuG40iwvPq?= =?us-ascii?Q?5k4/2wcbRGRMmq8WytH4wwoIElKJAqPmnmpMfD105w=3D=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CO6PR10MB5409.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(376014)(7416014);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?P8ka6OseTl+UsO5Bkc9CL7PcPA09ucVP7UwciL35YmS7yMfcKY0uXRH6Eq5a?= =?us-ascii?Q?8Fl+e9HXR2ikVgjMVELKUO1xT69ZS3ITaAhdjfRE2bPg9wvQMNWbe6wf4ILs?= =?us-ascii?Q?sZDq4m4+CE5B8Nyt9ygYyOR95nSKWVsJ+QTcFoi7xR/x8xM76nsW9+fN9dMd?= =?us-ascii?Q?9jPv8M40e+ym9CkTwuuB9rBZOctSk136TbUvQ6AaDFdgPivgfZjwTB4/fHD8?= =?us-ascii?Q?xhLBLoPsbrjyAX9wG0EVTGYX1VsSC+Oehw1epn/MWCYmt0fnN7AlPX1Sk6vx?= =?us-ascii?Q?fNz8yG1ycy2eEUYXYM54Q8lODzz2PgImQuS45WcADK4931TIzI3fkwXlTb5I?= =?us-ascii?Q?xoidDeV1Dy18aDehUx1RoE9YO0cXpp1bucodXjhlxRUvHg4MztJ/WIOVxXYw?= =?us-ascii?Q?u3vEmtQbA1FI7pwcvZ6JvJhQOJYgzmuFsVseDzrobo9YM+2OMZN5waRCzKgy?= =?us-ascii?Q?HrbCm9uLVOBLnPL65p4JWMFY9TKySYByuPKwPS9DxlEaOyK6UzRQmP4zUvTX?= =?us-ascii?Q?nqaye04t/gQPVvUZmLDWrPjvnucx47fe2ncMxVFl7GaMgyHmHfPA+XWGKPbb?= =?us-ascii?Q?HUg+86nPRNoN9lL5nL2LxmNrDyVvGj0gKkvHEcZVbUMTyo+x1KmMS3ROIxJv?= =?us-ascii?Q?+eNMFYkVPbzK31QWqKRy5nEvZq1glfGZ7ldMHzT9o0Il8x79FFU3nOSy7UWE?= =?us-ascii?Q?EhzZXG0ctCJv0qr8M6s2Vwca6izLH7u1M0b/jF9jE3RxuY5pErPlpbcfFs9d?= =?us-ascii?Q?stpWbBvaTsIaqq7pUeqN7hM969JtUNyyJgDL9sIhOsmg+1vd282Lcc7LHoZh?= =?us-ascii?Q?vUJt+EB6AbVT5NVz4MBza2x0gSUAXxgXPaG/iDa+gSdZRhKAFJNriP2w2iBM?= =?us-ascii?Q?hweS+7zM8cnz7nh96ZaF6lJ94o2b/RnWu2rmix9tJgRNk1tDREh+1RaAIr4c?= =?us-ascii?Q?2IW18Lo/qo03i4kbM5ZCoTrxKNYZyYB86FTdWmiIpBJ2KAzsveWHv1A7KLNm?= =?us-ascii?Q?Dee9D9edIDTakqwajFkzWXsWxuP8aD4dL/p/3wnJL4dCZSWuM0wZTUEprqMQ?= =?us-ascii?Q?+SYs3W3VZl7CHcWrIpAahGEc3qwlHZ2Fu/ZqR7jJwdSNx90ULdkBk3ywXCSd?= =?us-ascii?Q?n8+nVmKY0bFZLxe+54Uis5esHTLuZgJx4HBiEOgY0ytu1E9MfiXkg0uH9TGY?= =?us-ascii?Q?HoqhBSyHLPJ/wQDf5QsXkeD12TLdNWjx5kK7UU3Ci2xXC1o0nXtL5juf/481?= =?us-ascii?Q?nlii229Uk1DdJP+4+G9Ur+xtw/7FFdPSBRaS+CqLy0msRzGNIHyXqbU7ceoc?= =?us-ascii?Q?0oIm7Sh3iG9WYxGlx/1y3X5OPriQ//X9FhMGyboOFEKzSNcgJxE7c47XqqDW?= =?us-ascii?Q?eTi+Oi1zc77cZvWKzMcsPHXe5hf5jjIY4m0PEzopxyPkZl/FXCPYZrHFJcwl?= =?us-ascii?Q?2XmKxQl+/ZoLOKnEI5GBg9MRONSCy7viOuIGKNbBXdWhAjDMIOf0bGUb5rKH?= =?us-ascii?Q?zhvKE0vKqLChHLmLjwgivWZpbCTrJ0S6HHcrLOor4P6p7EviAXKbVUNzbBbE?= =?us-ascii?Q?UyTMj6JZbcvso7gQRed1yFQAbPjSZwkZV5Jj4m5BzkQNhTaALmNsSxsoQIha?= =?us-ascii?Q?Hg=3D=3D?= X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: 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 X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-Network-Message-Id: 13bcf6b9-0ebe-4829-3b9c-08dce895644a X-MS-Exchange-CrossTenant-AuthSource: CO6PR10MB5409.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Oct 2024 19:05:51.0793 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: PjPfZDbudgZvowpsZrIowmHPfveGJ74tgc2so/KCv8CCtS9csx/2SlcqRdDZ4JuHuTuG7IkBJDJfOvKBQhtkpPw33xc43NVUCnw5FTqYKIA= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR10MB6514 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-09_17,2024-10-09_02,2024-09-30_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=649 adultscore=0 phishscore=0 mlxscore=0 suspectscore=0 bulkscore=0 spamscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2409260000 definitions=main-2410090120 X-Proofpoint-GUID: o3sbUCmOwkjMouN9lKdFk-e1ef_hjTLd X-Proofpoint-ORIG-GUID: o3sbUCmOwkjMouN9lKdFk-e1ef_hjTLd Ankur Arora writes: > With PREEMPT_RCU=n, cond_resched() provides urgently needed quiescent > states for read-side critical sections via rcu_all_qs(). > One reason why this was needed, was lacking preempt-count, the tick > handler has no way of knowing whether it is executing in a read-side > critical section or not. > > With PREEMPT_LAZY=y, there can be configurations with PREEMPT_COUNT=y, > PREEMPT_RCU=n, where cond_resched() is a stub that does not provide > quiescent states via rcu_all_qs(). > > So, use the availability of preempt_count() to report quiescent states > in rcu_flavor_sched_clock_irq(). A note about the inverse of this case, where we might have long running loops which only temporarily enable preemption and thus would be unlikely to align themselves with the tick: in prior discussions [1] Paul had pointed the need for providing for forcing a context switch in such a scenario. I had a patch which did that, but I think it is unnecessary since this clause in rcu_sched_clock_irq() should already handle it. void rcu_sched_clock_irq(int user) { ... /* The load-acquire pairs with the store-release setting to true. */ if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) { /* Idle and userspace execution already are quiescent states. */ if (!rcu_is_cpu_rrupt_from_idle() && !user) { set_tsk_need_resched(current); set_preempt_need_resched(); } __this_cpu_write(rcu_data.rcu_urgent_qs, false); } Paul? -- ankur