From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from YT6PR01CU002.outbound.protection.outlook.com (mail-canadacentralazon11022139.outbound.protection.outlook.com [40.107.193.139]) (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 E67AD2E413; Fri, 9 Jan 2026 20:21:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.193.139 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767990088; cv=fail; b=tA7QP82tA6cCiPUdVv3L+q59guV2maE1e7BXR3um3103BdIdAts8gB5Sy8CqMJf5E0ojSeKgHrKUB0WMIumQkeDtVDydfuKOSW6UP42joQRV3HqWZILhCQyW49ehuLZGBX1+/LCn9PTK8IJikXdjw84EgSnEhQtCWG/3XC+fMLA= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767990088; c=relaxed/simple; bh=3/n9/6GHYiljqXoD2fyHpKXXcCnsGCz9QD/q7U7EyGI=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=AKcBlYehEtApU+fxFMr5NfleT6TSKXPWD0okSKGqakRpqLELzbmZLH7aqVWNF0x9kLHiydojPjOFLO2U59xSspcl9uE1UprDPrqh2E60H+RzM006bqjhk/RHbrGeHH0K7tM3GmhVugTwFvoasCBMUEijLSCY5G9iI130BmKcNOU= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com; spf=pass smtp.mailfrom=efficios.com; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b=o9lUQgcz; arc=fail smtp.client-ip=40.107.193.139 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=efficios.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="o9lUQgcz" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=F2j9MPOFfeGssy9RU3VEpYmpm3g1mblS0jf8qoirk2zhnHMIEq563d+yORwciDL6ruBJ4yR2VSkUprHl9VGGnun0cGcNCemGj/zZECKj9SItSZy9lLjG/E7qMfXDDKnKjXJOim18kQ4qfFcGMZd48/kxnb+2eV8JhuLTXBWDunShbimuNDaG5++A7/8Tc8PZlO99xMm9bbvBX6pSJ+d8xS8agCmuR5RLRx84+0eornO0bB3eYH0ah4yETUlmbAAc/fr2Onx8lMYwgysVWKt6zRuyIXhn5B7EGAtD+J/uWkj2Ov7jgagZ+5bMihjlojc/Zmqj/9nOYS9M7H++HZxxkQ== 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=5Lep/mu9VOEtneMBIgqd7cHhIjSSKeTwkoU3pUPY0oU=; b=WMr6eQEhUWfu5i/tIq94quH2QRKatHwkctUgqv+UVoy36qRWQ0FuDOpdvQcOochzCP3dLpuwbpUPLJRbXP7mnk1Pvd6KS7RdxCm53g8yj04gx7EW6wycYhV6xrrP3rQyuc56dTxwuspF8aiKo3DmglalMPO/wyIM6UlM/qRU1sq3mneJLOzHGHTQ8O7CuxWLQ1UAVquPjuubpVf0yXsNFm/5G8DZyRvtOshCOFdjQMf88GcpNa8EjVJAIF+DEiE5CJ75mMJkuaDV4xWSMy/TbHtHl3q87dU2JQwxt7vSwL+vb512RsTt62Ie1dBEhhpQsSPhWAqvIp1/H6wP+Vrvvw== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=efficios.com; dmarc=pass action=none header.from=efficios.com; dkim=pass header.d=efficios.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=5Lep/mu9VOEtneMBIgqd7cHhIjSSKeTwkoU3pUPY0oU=; b=o9lUQgczEFqIHf1/BhvHHOeid+3K2hqV61XMUUDgPITfbs7j2vocMSeVmjOL6DPNapawKZNvn0bOCZ8rjMKh8lBJWCmhRwLjfAgFraphivEWF9mmQ+3ZpM+mRXmBLNyzTw4kawnPxe1KjmSIc7GKoJ6nwxJxU78I5wYpGOB9WRp776DMoZHFtBai1u/+7aDUjuq8MuvpnrNDeDNECN7HIpgveSSeAhZxlb1nOgCi8yh/xy0BtXk/pxCbyRwETqz55VG49p8kkItHIdf7nWQiV4lzvl2uP5/xIGG2nvhccOddh3uodsr1vLd+Ri68uC6JpXRDP66NNYnQx1MFatPhWA== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=efficios.com; Received: from YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:be::5) by YT2PR01MB9509.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:bd::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9499.3; Fri, 9 Jan 2026 20:21:22 +0000 Received: from YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM ([fe80::6004:a862:d45d:90c1]) by YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM ([fe80::6004:a862:d45d:90c1%5]) with mapi id 15.20.9499.003; Fri, 9 Jan 2026 20:21:21 +0000 Message-ID: <3c0df437-f6e5-47c6-aed5-f4cc26fe627a@efficios.com> Date: Fri, 9 Jan 2026 15:21:19 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5] tracing: Guard __DECLARE_TRACE() use of __DO_TRACE_CALL() with SRCU-fast To: Steven Rostedt , Alexei Starovoitov Cc: LKML , Linux trace kernel , bpf , Masami Hiramatsu , "Paul E. McKenney" , Sebastian Andrzej Siewior , Thomas Gleixner References: <20260108220550.2f6638f3@fedora> <20260109141930.6deb2a0a@gandalf.local.home> From: Mathieu Desnoyers Content-Language: en-US In-Reply-To: <20260109141930.6deb2a0a@gandalf.local.home> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: YQBPR0101CA0246.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:66::27) To YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:be::5) 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: YT2PR01MB9175:EE_|YT2PR01MB9509:EE_ X-MS-Office365-Filtering-Correlation-Id: 3d6cd1e7-831f-4a88-545f-08de4fbca72a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024; X-Microsoft-Antispam-Message-Info: =?utf-8?B?Q0xwNWdwbWZSWVRSZ2hZdnVyTXZIc0lkdFlCamVVeUcrckxRNlRIOFNGMDBa?= =?utf-8?B?SWlMZFpHK0FWdGtQNGl3ZHBXSTB4U01pcnJLQlE0UmovQ1Nvc0tkelRKd1ZS?= =?utf-8?B?a1dwOXVmUXdZNFM3elF6NUVJVVpraS9ZczFhQ24zdXhiWjFWNzZVbUJGR3dx?= =?utf-8?B?Kzk0N2JuMjkyOWkrZ1ZlNW1jckFRc1l0UWFVSitkNHRyRURXUHdlL3IzZmti?= =?utf-8?B?UmdBWTRKdTFjR3lab3V5dnFDU2hITHN1aE1NYXZwVVVIZnFOd3hRM1M1WC8z?= =?utf-8?B?YUkyMTdTWUE0WjBrVHR1YlU4Q2FJS1g4Q3RnTGdyTndqd0hBeWJHWDFUTkhY?= =?utf-8?B?RkxzWDZoSE1xbHpFWGJwOXFPOW44REliTW9JM1c2T1dwU2I3R2NJWldLQlJv?= =?utf-8?B?OTdRUHV4T1R0clpDa213RTgrcU5KRTRHRzJRWnRKc0FIYVVXc21CMDNzd2Mz?= =?utf-8?B?dk8razdMakJXd0NzemowTFFaMHFHSVFHais0V0R6dDhiNVJVVVRjeHgvNTcv?= =?utf-8?B?N0NyTmdNUlBHaDZ6ZmVlYUlhYlBHYnBZNFMrNFpNWFZiWmFubFMzNDFWcUV5?= =?utf-8?B?aEd5Y0ZlWlA1VDhINDQxQVN6QlduZmhzeWw5TVV4K1pEbWg2bElEQnNGL0tY?= =?utf-8?B?Ymo4azVDTHFZZnJFTUpjdm1wV1lOeFp4dlR3Qnk2L2tFWW45VVo1WlArNjlV?= =?utf-8?B?b0RXSEJaWmdVeXRBdnFDcndhS0x2cyt1ZHhMZWM1dVpBZkUrVHdnWHVWbGJE?= =?utf-8?B?UmQ5TkR2dENzQWhQclZjaEpKNmJlR3hvN0VDazFCd0lmTFM1Y05MR3k4ekZ4?= =?utf-8?B?ZmRKNW1BbzNvcExCVnFob2toOVY0UVBLNmJEYUkvVjZDMHdxb1Q4RHpZK3hn?= =?utf-8?B?RXBIbmVuUnBmeVdrNi9yc1JqNHp5ZHBlakF0dDEvUnppbnVydTU3SktGYk1n?= =?utf-8?B?NzhKaDhqb1FGV1hwQ2djNm5QMjhJQzI0blM1d21lNGc5UnBUSVRxcG1hVkFo?= =?utf-8?B?eHMxRXNLTGtOMnRhZ0NPY1Vnb2d2bnJwdXlNSXBJVmJnM0wxc2VqZWplS1JU?= =?utf-8?B?SXZEZkJrTEVaSmY5MVI1Sk5NV0dOY1dtTWh0YXVXcjRKd0o1SmtNbkNGdzNj?= =?utf-8?B?OWJhMWNCcitaQUNZcS9mZEUzb2kzSlFsNzc2SFpULzBlVWJpS3hjUDdEUDBs?= =?utf-8?B?eG5SdGY0b2R4bHIwN3RDd2dFN0x6ZmpTWG9ZdkZLbTNQL1cxQ0FWSzNnRWN5?= =?utf-8?B?d0srUzdaQ3pDNXVSbTY0MWNBcTROcXZUUkxLdjdxQUVqamUwYlBNNFlIOWNI?= =?utf-8?B?RTgxL1JZdjVEVFZFUWZ2M1lqb0xGd1c2REdyM0hmZis4MFlzK3FrWndhSmxi?= =?utf-8?B?dzBhbEZjMzdTM2RrbHU1c1JrMUxLWUNDRENnOVcvUG0wUnpzNHN0VTVCeEtR?= =?utf-8?B?cXpDK25zdElSMzY4a2NtekNMSVAyeUlmL3lsNVA4YytBUCtDQmJ0RjJyeWMr?= =?utf-8?B?RnVXb2ZkZnVtQy9YZ3dURWpRTkhkUkZ2MFdEcUUyMGk3b3pyTEIxcmxSVXBp?= =?utf-8?B?SnQ5VjZDY3ZpdEQyVWVOV3ZWUWVwQkNWS1RqQjFBWk9MQXU4TElia2F2U1Z4?= =?utf-8?B?NzRlMGx2clphNTljVnVRQjJCTWR1NE1xWmZRbDNEREFRZ2cwaDhQVFVMTC81?= =?utf-8?B?L21GelNpcEJSRFdMYXZheWczdEVjTXpnN0JVblpzSWY4TGhtcHdXREpzRUZ0?= =?utf-8?B?UGhZWGFaK21sUlNXaGNCOHN6emZHa3EvY3JGWmJZTEFHZU85U2lwcERVQnM0?= =?utf-8?B?eWxMYVNWK3lzSXFOUjZwVWVzbXFRR3l4RTZKVlRnTWZsWmlKbytpcGQvYi9I?= =?utf-8?B?NEk4elFKZWFDZ2JDcUwvWE1FTFBWNFFXQjNhZ2h3V1BFV1E9PQ==?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM;PTR:;CAT:NONE;SFS:(13230040)(366016)(376014)(1800799024);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?VEt1RlFISEZpNGl4LzZrNThISHFuUDF2dGREcjR6a3pQZkJMajZ5eWdyTWlr?= =?utf-8?B?YTdvc25kT0YzcXV5LzA2UGRsT01vaDZZaG11YUZ3eWRtV1VEN0M2Z1BVRFJt?= =?utf-8?B?VjhmejBCa0VhSHo0L2N4SjR4UWtPQ0QvVTJGKzA0NjdvblBpVGc5UWVkU1Jp?= =?utf-8?B?eTVWd0R2UlFCN3NNYjRJeWI4cnFPNnlvZ0N3VWNkUkxvdlR2Z0w2S2k1b2NZ?= =?utf-8?B?YUlYdjFzMWNnVk8vVHAwdXppbFdpemw4NUZoYXo4c0VOTEdMZGxENHQ2Zksv?= =?utf-8?B?VE96ZXpsanpBVkxZdjFuMzhBZ1ZkMWpIVitqT0hYVkVsdEJiSlE1YmNXWkZl?= =?utf-8?B?alFWRThnV3R5RE1UQ1Vua0g4cmUwL3dTMFFvQXdsQ2pvcGNDYUNTd3N6aWhC?= =?utf-8?B?cS9zQXJBL09qcGtDOHZLOGJOMCtlTFVpQjJlRVRPc3h6ZWN3dWQ5WUVlb1Fm?= =?utf-8?B?OUg2ZWduS1ZiTnE2RHZQNkxncVg3T29EOHV6VFl1WEhxOG5Lb0svb0RpMW1j?= =?utf-8?B?UUVQYW9YRURLY2lRNGIreHdkcnpPb1ZkNmRBbXFxL29CL01wN29KTkk4d3E3?= =?utf-8?B?Skkwa2RHM1pXVjAxQ255azlsWWpyMXlyL0ZQVVp0bG9tM2dBdHdFRHRZUkxS?= =?utf-8?B?d0F6WkRjRXRsaThna1RsMldjY2M2Sk5DVG9Za0dvSERLa2wrUlFLRlBXSkhk?= =?utf-8?B?UXdMeFhUdklNOHhpUkxCOFBiVnIxRFF6Uyt3QVgrMVZDdlovTUs3eS9iUGYx?= =?utf-8?B?djJIYWsvVCtEZC9GY3Vab3liOEEzblArMzc3aXNKOG9QODVKZWpnZVdkaWVZ?= =?utf-8?B?S3E4cVVCampRK2JXZ3NLUGpTWmoyR1hVaUJEZmVjRW9rRGJwMVhuQkk2Tm5U?= =?utf-8?B?ejR5alJHaFNBK254bUw0cldsanZVdXAyRmZYRTVGajBBN2dzemtSRTJGbFhM?= =?utf-8?B?TjRLQmE3OWdMM2pYbDY4ZERiQW5RY0hsMFhPUG9TQzFBUzJDNGdmbXpDU2hG?= =?utf-8?B?VG5ONEFHWEM2R05Ud2twN3I1bmRoZnliL0tOeHNnbDdLVmFmQ1BtS1BOMUJH?= =?utf-8?B?VFRNSjZCeU9JT294RGYrb0xaQUFSSmRhVTN4SEpyLzhsYkIwWFBCb3JBd05C?= =?utf-8?B?c2VhM3I1SFNsSmRPNWJ1aW1ibExoUVVVRE5hK0hiL2trTXlQYWJyN2VmbE82?= =?utf-8?B?eUJTTFhNZlZ6ZDlpRkxKY1c4TG1LL3UwSkJjSFA5dEcwRnFJS1p2c1VXMTJZ?= =?utf-8?B?QjRvaXAzcHY3NmpPY0FKMWtpR0NZQXFyWVoySU5VUUx4QmtLUnlQSVdpSksz?= =?utf-8?B?WjhiMnc4UW1UVlgvZktVTHdyOFZkYzYxRGdhanZkVkhWVWI1TEUvZ05sUTY2?= =?utf-8?B?d0Q5UlFkeE10N1BnV2k4bXZzMVNRMDJsK3lUb1VDdFZCYkdqb2RzYi9RTHAy?= =?utf-8?B?VGEyQkF0SjFVV3ozWkRqcWtyR1Rpa3A5dVp4VzFRUGU5c3p5aUtOMmtmN3VU?= =?utf-8?B?Y2hmNTdoSjVJVVQ1bkExZW9zalJLY05DQ1A4UUllUElCRm45RDM0RHRwTFlx?= =?utf-8?B?UzFwTi9iaC9WMDBMeWFqM21MbVFMeFUvYU5SZWh2WHBmb2c5Y0V1RkNTdkxQ?= =?utf-8?B?SDB1QVZFbXk1djNDdkZlZEFFczRxMHNET3loZXB0aXZKdXZNM1pYTUZ3dC93?= =?utf-8?B?L1NlZmkwU1RLK0hqeVIrc0Q2NWdlWVNOMVZZSEl0U1FvdTFkc1Y3Y2lxaWxs?= =?utf-8?B?QUJ3Q3JsS2ttMWJxa1E1YXdpR3ZKaWZ0V3lGTlpITld5K2ROb0dCK0hFN0Nt?= =?utf-8?B?QnBHM05CS1cxQTNYWWEzczNmc3lRZTRiMWlxcWlJSXltTFpsSCtrdU5haEVz?= =?utf-8?B?OFluWHl0UGpqTE41MnUyRlNzendaVjBETys3dDMxRFhxQUtzWndSR3Z2ZGtp?= =?utf-8?B?UkwrcGptUE9JdldLOGZSZmx6ZjFHS3dsdHhnYXpJek0rUkZSTWt1OVBrUW1v?= =?utf-8?B?aUxoeXVjaWl0VDFIL0U5UkgrMnliQ2dzVEZYZTBUNVJoaGNRQ2RrVHJRc21Y?= =?utf-8?B?QU95d3Ava2w2NU5xVnRnM0hsOHJnVzUyMFFIWW9UNG1VMVFEWTBJdUhPS2hB?= =?utf-8?B?cXVhYlg1NS9JcTVzR0tyMkt2TGtpY0l5TW80S1RYVTd0NnNqMVk3RGRlU1Vm?= =?utf-8?B?Q2syQUh0RTdyZGhxaG5WeGk3b3VnYnlZVUUvbWpqOGlFa0poZkhYMEhOWE1u?= =?utf-8?B?N3pCR0dZbXBCY05rQUtsaDZxQTZxdDAzMHFiZ0pUTmoxdHIrS3UzOHo5Zi8w?= =?utf-8?B?MXBKQkdBeFhMSGZwWGF0b2JJMHJWSXl3T080SU1FUU5GdzhybFZyY1dtb3Ey?= =?utf-8?Q?S//gPKzoIZ2PXStw=3D?= X-OriginatorOrg: efficios.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3d6cd1e7-831f-4a88-545f-08de4fbca72a X-MS-Exchange-CrossTenant-AuthSource: YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Jan 2026 20:21:21.1815 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4f278736-4ab6-415c-957e-1f55336bd31e X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 1+0NO3Y8V/voJZKvDvk1G95KRcN1xdnDBIywBdO7VJg42PrbmQkTbT4AaescjDWwlIujWV+NyMofJrNZ6DJDj8LOsL4T0wqjgjI7T5yt98w= X-MS-Exchange-Transport-CrossTenantHeadersStamped: YT2PR01MB9509 On 2026-01-09 14:19, Steven Rostedt wrote: > On Fri, 9 Jan 2026 11:10:16 -0800 > Alexei Starovoitov wrote: > > \> > >>> We also have to consider that migrate disable is *not* cheap at all >>> compared to preempt disable. >> >> Looks like your complaint comes from lack of engagement in kernel >> development. > > No need to make comments like that. The Linux kernel is an ocean of code. > It's very hard to keep up on everything that is happening. I knew of work > being done on migrate_disable but I didn't know what the impacts of that > work was. Mathieu is still very much involved and engaged in kernel > development. Thanks Steven. I guess Alexei missed my recent involvement in other areas of the kernel. As Steven pointed out, the kernel is vast, so I cannot keep up with the progress on every single topic. That being said, I very recently (about 1 month ago) tried using migrate disable for the RSS tracking improvements (hierarchical percpu counters), and found that the overhead of migrate disable was large compared to preempt disable. The generated assembler is also orders of magnitude larger (on x86-64). Creating small placeholder functions which just call preempt/migrate disable and enable for a preempt RT build: 0000000000002a20 : 2a20: f3 0f 1e fa endbr64 2a24: 65 ff 05 00 00 00 00 incl %gs:0x0(%rip) # 2a2b 2a2b: e9 00 00 00 00 jmp 2a30 0000000000002a40 : 2a40: f3 0f 1e fa endbr64 2a44: 65 ff 0d 00 00 00 00 decl %gs:0x0(%rip) # 2a4b 2a4b: 74 05 je 2a52 2a4d: e9 00 00 00 00 jmp 2a52 2a52: e8 00 00 00 00 call 2a57 2a57: e9 00 00 00 00 jmp 2a5c 0000000000002920 : 2920: f3 0f 1e fa endbr64 2924: 65 48 8b 15 00 00 00 mov %gs:0x0(%rip),%rdx # 292c 292b: 00 292c: 0f b7 82 38 07 00 00 movzwl 0x738(%rdx),%eax 2933: 66 85 c0 test %ax,%ax 2936: 74 0f je 2947 2938: 83 c0 01 add $0x1,%eax 293b: 66 89 82 38 07 00 00 mov %ax,0x738(%rdx) 2942: e9 00 00 00 00 jmp 2947 2947: 65 ff 05 00 00 00 00 incl %gs:0x0(%rip) # 294e 294e: 65 48 8b 05 00 00 00 mov %gs:0x0(%rip),%rax # 2956 2955: 00 2956: 83 80 00 00 00 00 01 addl $0x1,0x0(%rax) 295d: b8 01 00 00 00 mov $0x1,%eax 2962: 66 89 82 38 07 00 00 mov %ax,0x738(%rdx) 2969: 65 ff 0d 00 00 00 00 decl %gs:0x0(%rip) # 2970 2970: 74 05 je 2977 2972: e9 00 00 00 00 jmp 2977 2977: e8 00 00 00 00 call 297c 297c: e9 00 00 00 00 jmp 2981 00000000000029a0 : 29a0: f3 0f 1e fa endbr64 29a4: 65 48 8b 15 00 00 00 mov %gs:0x0(%rip),%rdx # 29ac 29ab: 00 29ac: 0f b7 82 38 07 00 00 movzwl 0x738(%rdx),%eax 29b3: 66 85 c0 test %ax,%ax 29b6: 74 0f je 29c7 29b8: 83 c0 01 add $0x1,%eax 29bb: 66 89 82 38 07 00 00 mov %ax,0x738(%rdx) 29c2: e9 00 00 00 00 jmp 29c7 29c7: 65 ff 05 00 00 00 00 incl %gs:0x0(%rip) # 29ce 29ce: 65 48 8b 05 00 00 00 mov %gs:0x0(%rip),%rax # 29d6 29d5: 00 29d6: 83 80 00 00 00 00 01 addl $0x1,0x0(%rax) 29dd: b8 01 00 00 00 mov $0x1,%eax 29e2: 66 89 82 38 07 00 00 mov %ax,0x738(%rdx) 29e9: 65 ff 0d 00 00 00 00 decl %gs:0x0(%rip) # 29f0 29f0: 74 05 je 29f7 29f2: e9 00 00 00 00 jmp 29f7 29f7: e8 00 00 00 00 call 29fc 29fc: e9 00 00 00 00 jmp 2a01 > >> migrate_disable _was_ not cheap. >> Try to benchmark it now. >> It's inlined. It's a fraction of extra overhead on top of preempt_disable. > > It would be good to have a benchmark of the two. What about fast_srcu? Is > that fast enough to replace the preempt_disable()? If so, then could we > just make this the same for both RT and !RT? I've modified kernel/rcu/refscale.c to compare those: AMD EPYC 9654 96-Core Processor, kernel baseline: v6.18.1 CONFIG_PREEMPT=y # CONFIG_PREEMPT_LAZY is not set # CONFIG_PREEMPT_RT is not set * preempt disable/enable pair: 1.1 ns * srcu-fast lock/unlock: 1.5 ns CONFIG_RCU_REF_SCALE_TEST=y * migrate disable/enable pair: 3.0 ns * calls to migrate disable/enable pair within noinline functions: 17.0 ns CONFIG_RCU_REF_SCALE_TEST=m * migrate disable/enable pair: 22.0 ns When I attempted using migrate disable, I configured refscale as a module, which gave me the appalling 22 ns overhead. It looks like the implementation of migrate disable/enable now differs depending on whether it's used from the core kernel or from a module. That's rather unexpected. It seems to be done on purpose though (INSTANTIATE_EXPORTED_MIGRATE_DISABLE) to work around the fact that it is not possible to export the runqueues variable. That's the kind of compilation context dependent overhead variability I'd rather avoid in the implementation of the tracepoint instrumentation API. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com