From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from YT6PR01CU002.outbound.protection.outlook.com (mail-canadacentralazon11022087.outbound.protection.outlook.com [40.107.193.87]) (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 6F92A31CA68 for ; Wed, 20 Aug 2025 14:27:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.193.87 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755700048; cv=fail; b=Ua868QEMNxgFLdvuzaD5mFM9uL6SZwqSyQt556EhumuwT4TzHKlHN+bPNnFjt2gveN2p2yEp47yFUsl85c0p/ky9+APo2fB7CX9NSMuLR/yKUw2dIF+76vckUUGl40NzqdecRhywMKgBB6qTcvi2qhPJpAqsM44n6HiSc2l1Shs= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755700048; c=relaxed/simple; bh=bQ4lY9Y05TP2Dp5xfPwVx7nx+lpaIMxkCE5Jf7pU1Gg=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=qM+TJ80LKsqd7JAZjBw47zfzteuXIdpkXiH1pPcMZUqAiPMfZdCED4ls7kQt8DiD9F8RU3Icv0ikXVH3D74uIej+s5PdU1318gRDwUz0JNy3XFN2nUWXjeAZeeOVoOxvpwsurZh6P6AYPPccGfPmCpdm84ks9D11d4cnW//53yU= 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=roTDcDRu; arc=fail smtp.client-ip=40.107.193.87 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="roTDcDRu" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=wUNJs5LtN8m28kHKc6EIsY1sQy/oYd0bZSeWTT8mOEdfnDv5QPE/VmAOUkiV8qN7ZcW6Qi9UIPSsU2slsBElbsGTfW9ZTcdujGZzoCuAAf3H4eccArdPBdbPHjsoV/zcBR5EHFoXqimWgdGSrqD1PXjUhKJECIWX85ZR6TlYNvoPRYAlAOCb4iy/1kqcNxEvGxKeUEnnWPZXUuvImwWPeZLW57m1CXzlcpal4ClsvQgxJPdGZxoSsJZYSfCm21srU7Cjit6Q6NU18mpdx7yh5IBJhzkaicfCKwxfiJ/BzEGgrLFnlZYS7S/vQe9Mj3OutRft01/+kMbZHFvr57+e3g== 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=AitEwntjMmb4y7H8vm+xOc4vQjiKtYNbnKbg9nkUd9A=; b=oySYVVROJZ8dBu3BwGC8yQIf3GWohRONAmt5DbcKYAFJ5sYdkiCqucrSG+3DsS5eUg6OpHFr07HUA7TXNi4k9OCnfQIkX3RH2fcdYni353VRGbQ4kTbxV8gkYcvwqhXWQK8sBMQ185d4i/O8CNIh2sDXbmC06ymgNHnWp0xbK7vzPZbaAekoTroJBHvcU8K//lXdBdg5MW2cUDXVHKME9UB23oYvLNq8FVOQA1rpLjkmVlvrX2pyYqBToqqoVI4ziyD5Kok6NA5BtBrZSapyfxEwyAOaJ1iBRf43lkKc5ITgG8OyZ8RxOQwUhk61MNSmGGvEAAbONG/4N8bM0vQOKg== 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=AitEwntjMmb4y7H8vm+xOc4vQjiKtYNbnKbg9nkUd9A=; b=roTDcDRu9M18l61ooN4QwUSshlhQcIGAsdx9dmKscX8YjVPpKpNaHx8y5CAEfCd662Nurbn+KjsCAaJyLL2GjBhHx/gmzxE9XiVUTrtmwfALoW+6b+Q/FQVbrQr0A3P5UzJJpIQt7nK1BLWl4LTURrMd0tnVrx3hPXIqwkGirD6BDEN6tORdYO+RjM4DL2tuuy0rZeYEA/dAUoNDRCbWs7+r4V2R1+auX3xeLevE7VNsWqLt9FgHYzO7ODbL11b97rPTVajAu5ecG+GEFexgHQCY7F/7se5afOKbc+mqrY8hCntt3VrpkhrM8SP0VBvX4fqO8I+pt8a2fjl00eA2eA== 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 YT1PR01MB9132.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:cf::7) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9052.14; Wed, 20 Aug 2025 14:27:24 +0000 Received: from YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM ([fe80::50f1:2e3f:a5dd:5b4]) by YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM ([fe80::50f1:2e3f:a5dd:5b4%3]) with mapi id 15.20.9052.013; Wed, 20 Aug 2025 14:27:24 +0000 Message-ID: Date: Wed, 20 Aug 2025 10:27:22 -0400 User-Agent: Mozilla Thunderbird Subject: Re: [patch 00/11] rseq: Optimize exit to user space To: Thomas Gleixner , Jens Axboe , LKML Cc: Michael Jeanson , Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , Wei Liu References: <20250813155941.014821755@linutronix.de> <12342355-b3fb-4e78-ad5b-dcfff1366ccf@kernel.dk> <87bjoi7vqx.ffs@tglx> <6b428c1f-4118-4ede-8674-eceee96036c1@kernel.dk> <877bz67u3j.ffs@tglx> <87y0rh63t0.ffs@tglx> From: Mathieu Desnoyers Content-Language: en-US In-Reply-To: <87y0rh63t0.ffs@tglx> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: YQBPR0101CA0230.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:66::34) 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_|YT1PR01MB9132:EE_ X-MS-Office365-Filtering-Correlation-Id: c17fa925-be06-438f-323c-08dddff5ae3c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?TlhqYVlqVS92enVTUDdTcE0vYU1YbDNpeHRtdUJ6MkhCQmM4bHllUjM4R1Ni?= =?utf-8?B?NjhUVk9VWGpDazRKK09QSnFHR3dzV2FZeDl1WmZZWGlDR3plaVFhTVFPMWxT?= =?utf-8?B?dXN5Z3gxamxlUFVKM2dZYWVMcnRWTWllU3d3THh0QUJKWFpQbFRBQ0RTUVZh?= =?utf-8?B?SDZnck9weHBva2tuajVWYTRrU3RwaWw4VDl5cTdHRmlPd2t0UUZJMXZTYk4v?= =?utf-8?B?REQ4SGIzdUJlUFlwMG4xbHdBeDZ1MXNwL2ZRSnFvWjd6dTJQMFZpRG81ZGRU?= =?utf-8?B?TDNjVVE0WWR5U0RsYmVsRlhIN0cxYUdNNlRIWGN0b1kzaWwzK0xOVTBQMFl1?= =?utf-8?B?S1pGaWk3c2ZEZWxzRVNGTFVPb3k5WDB4bWZyeUI1MnVKbWlaaTYvc29MYmJE?= =?utf-8?B?b2VKYXBTSVpLeXBPL1JES1o3NGJyazBYMy9tdjVkbTNLZ0VsaWxjVElmbXpW?= =?utf-8?B?NWpxZU9CZkRLSUhjL3d0MVRwV1VqSzZtZE10Ui9UM3ZldU5TcHdmNHpwOW1S?= =?utf-8?B?YlRKakJkNGRvR2FwcUduazVVTmZUbFJlMTNFSXRBWUxaT05IMVo3Wk55eXlO?= =?utf-8?B?bS9SUm0vanNIVkhFcHpkbkY5NUlrRzhQK2dnWW8vOFBuR1VzWjRDN2MyUFQ1?= =?utf-8?B?YnZQQUp6b1pvVTRyWmVvNWZLYXFkT1VoblBXZTMzbWRFZjgvNXdlSDd6UFBa?= =?utf-8?B?TWJRcDBpeHdDN3VVdytwaHhlOWxxRC9Ra2JyUFhMcXJLeGNETFNWUE9sSGVP?= =?utf-8?B?VmYyd1pkM2g4aVpUL2V1a2x5OWx0QlVubmpEb0hKNTJCajJnUEpmM1hGSUFE?= =?utf-8?B?b2w3NElzbUNKZEdQU1FJRS8ydFRyazVKZzZhWXJQZUJiMUN0ckF4Mm9WVWNG?= =?utf-8?B?UHpZVHgrbjFLL0lmRXVIU1JRb0RNQ0tGeUQ4eUFOdDA4NEI3dUYxMnloaUJK?= =?utf-8?B?ZVhZbkRibWVoaXhTMENmVlhKazF5TG9IUVdvaUVNM1dEakdnNGNlMmE2RndV?= =?utf-8?B?Z3U1RXpNSytRTVAzdm8yMFBMQTAxbEhCV2lWUkI0Y0FrRGNVTUNiSHgzMU9p?= =?utf-8?B?VW1LZ3F3aklkMHlySzZiQmNtNmswTDNYMnUvY0ZGemJHQnNJbTZlY2ZmNHJr?= =?utf-8?B?ZWVBekZaK3A1T1BCOGY3MktjUVVSQzFtUHNNNjlSS2FOQUhyZDV1VW80ZDFC?= =?utf-8?B?TW1XL2ZUZkpJTytNTUdmbjJsUWVRVGV2MHJLb1JlVlBFOVlWQTB1dFA5L05z?= =?utf-8?B?eFMwajNDNEhTNDlMcHhJMzVkdzJUTkdLdFNXSlFQaWdMUHNwZG9ZaWxrb2w5?= =?utf-8?B?aEMrOFcxZ0NoTE8raW9MdDFobEZPVmE4SHNVZlNvdVZLeDdLVmZYREhDeERk?= =?utf-8?B?VWQ3WUhqcHR4cG14Vm1mbnlMRUs5aHFhREN0VCtFUmZGWmM1Y2hzVWNsQWFi?= =?utf-8?B?WFg4ZXByRld3VUtiUGJlZW1YM2pBaks3dEtlUGwraVA1eFpuekNQVGhDdjNI?= =?utf-8?B?QmZmb1RNK2p5dVNUQnVTTXdrT3hocm1CODFSKzc5dGk4bjVrL05ZQWtlV0pz?= =?utf-8?B?TG00UENlQ3lKYXp0R3lvVU5rUkUwbHA0SkRHdDRrUGl1VURSaGFYREpRNjNO?= =?utf-8?B?MnoxSXNTTGN3b2EvY0psVi81eFYyVFFiM3gxbE93Ulh3ZjNIaXR0WDVTMitr?= =?utf-8?B?cytJTFUwZlBHODFIcWpnQ3QxTUJSTFRVVk51YVJKVFlxM2tKUC8zdWRZRGpl?= =?utf-8?B?Y2hXM0N5OVdhZmd2dnhBWG9KU05GN205NUdUY1JHRzBkNjBVcVpRSk1IdWwr?= =?utf-8?Q?tQQ/TwSJ5cSy8eCbZBjhsZSIuLcYBkhoyngiU=3D?= 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)(1800799024)(376014);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?UG9MWTZZSkdxN0VaYTBPZytCR2NyVzUrcGgyZUl4akRwNDhVbjNsY1J2Tnh4?= =?utf-8?B?ZkF2K2NKQXY0YThIY2FWWnhLN1B3aGZxcll4WEhTUnNRSi9LVHhadmp6MzlD?= =?utf-8?B?N002cTBWWlo2MnZtQmoxNU51VzlpVUZaZWQyZ2RDTVpqZTlKYW1oSXBtNDhy?= =?utf-8?B?WlZwcGc3dnhGMVl3TVJsK25XV1JNakxIUVE1OStzT21jWmZCSG1RZk1sT1Fy?= =?utf-8?B?cXdmcGpUMW1oYWVDcG1yQjBVNXNzVHV5TzdXVk9WdHhtR0dSYzhCQ2tPcEZN?= =?utf-8?B?eWZPMDFNYUtsR2pFVTE5RkZlZHRxaFgyNlBZeXEyV3dTcDJ1VFRpbEtzcFpx?= =?utf-8?B?azU4d3RoYStDdGlpWDA2aExWWnBJTzVXWXdQTmlIeTVDQzduc08rcGVyZGdQ?= =?utf-8?B?RWQwQkUvcDNtN0tiMXNEOGU3QjIxd3pNQmRWanlzZyt1bmpzTm9WMWdobEFN?= =?utf-8?B?clc4OHAwUE00R014KzdsVkZOREg4Q0huRXY3QTVMWkU4aU80ZEs0ekM2bjN6?= =?utf-8?B?WHpxOGIzNlY1cVoveGMzQmJhbnJZRWtDYldWYmcvZ01PN3RnUWhGMEFUQXZw?= =?utf-8?B?UjUwZVNtdDJLcGRTRU9pbEhOeWNNZ0FRMHlVcGJYVUszZmdSSVZ0Z3F4Q2ls?= =?utf-8?B?TU5oTFdGRzZEZlYxRVBkQXlwOFV0czZYM1AzVzRIdnJhMnpVeUUzZURPOEE3?= =?utf-8?B?L1duUG9XYStnVzM3alY1dklzL2lmZnl0RzhiM1BwbE9sSkhsTDI3K0lpOHhH?= =?utf-8?B?VDdhR1VjcCs2bjlZYTBJOVhGTDFQYzhlM1JBUnhmNnpSQlZkL0pCeFpEQjNj?= =?utf-8?B?TkxuMktMaEF5eDlnOXduVXpsWVpxUVBWM3puTU9zZTZKSE84NFFxZ0V1ZCsx?= =?utf-8?B?QWdQZ3I1TDVSRjdhQkxyaGozdGpZakRtQjUrVStxcnRBY2tXZ1BraTR5QjB6?= =?utf-8?B?NkpPVUt3WTdQMzdVM1dZNEJ5TWNJaGxkcTBsT1pxOTJrREZyYzZwZlo5Z0w1?= =?utf-8?B?cXZBSWpJSy9ESGIwM0hob3V3Wnpkc1ZVcmkxSlNRT0dzc0t3M29ETnhlREln?= =?utf-8?B?VnhhWVZYY2gxQkdma1BRWkNEQk1ZUUNXanpoV09zN1VBTW04NkVLVUtGSnVn?= =?utf-8?B?d3FjeVZqdXU0WnFoaXdkd1ErS2ZNSzh1bGswSzdVdkJXOVpBM0tMWGwzL0Rt?= =?utf-8?B?RS9Pb3lhL3lyWVhEQUZ6UDZtYlZRcTY2MjZUZElMeEFWK21lQ2xseHN2Qk9x?= =?utf-8?B?UFIvYnh4aS9XK2NuNU9ENU85azZzREcxemRkRkF4NlQ0eTE0cW51aG5ZK2ZG?= =?utf-8?B?NktSTzNDd1ptdzU3dUZVSHNqMDNHNjgrY2EzYUl3MHN3aVg0ckpGQnZHaGlP?= =?utf-8?B?Vi9PS09LVGhxT1lPTWlqVzBla283ZUZpcHp2MEU3Vmo1eU44Ulk4a3Q0NVEr?= =?utf-8?B?M21IN3pNUDk3M0U3eXczMmVmZE5tRkhtQUVManJpNmgwcDRtWExCZ3JNRkRQ?= =?utf-8?B?Rnc4WUpzZnhHOC9KL0xRaU9jdFZnU2RyYktSdDRRaG82c1hud1RrZ3pFVVBZ?= =?utf-8?B?NG90NTZBNzhDR0ptRnljVElxT0NKZGpjc0RuZENhYU5tOHFTaHIvR28yNGJ5?= =?utf-8?B?TzV4KzNraHZKOFIvVXprMmk0VlVVMVpZY1VOcy9CU3o5U0NPaGhiYnU1WHBF?= =?utf-8?B?UXU2UDVlWk1IbC9BL3l6QVVjOWVTTkdxOU1Ob2Y4dXNYSnJ2MHMwMlkwczRF?= =?utf-8?B?dENMY0FhcTJ2TEVsa0hMWUQrcERTd2RvMHhIVXdUNGlpK25HbkE2R0Z0emht?= =?utf-8?B?ZnFuUVpPa2pUR2RLR2Q0K3k5U0tZL3FkcXc4UnA4aW5XZnVrQkZYaDZ0NWxI?= =?utf-8?B?RU9lak4ySjVvS1VtRnVYVFoyWFpaaUx4MVByRnU0NFFOWnl5a0tvOGg4WUJV?= =?utf-8?B?MVhXT3F3aWpaOW5EaGQrSmkvbDNIQWFZVzFZMjBpNjM0L3FGL3FKeFJoazlZ?= =?utf-8?B?UHhKbnhUck1JYXZRTjhlaFFTTExqVjRwbk5ySTNjM0xsYitJeHNLK1pvNzF1?= =?utf-8?B?Wkd3QytDOEpnTUkzak1QRGJKcHBnbmZQU2FFWWxJVkdxdFBxRGRrVVRQYUNx?= =?utf-8?B?SkN6RUpOWmkvdkF6Q0N2eWZJTFFGL1owTkhMUitNSFQwTmFjeTJGSjBKTThO?= =?utf-8?Q?Cxl3aycC1l//E6+c+9PvGzg=3D?= X-OriginatorOrg: efficios.com X-MS-Exchange-CrossTenant-Network-Message-Id: c17fa925-be06-438f-323c-08dddff5ae3c X-MS-Exchange-CrossTenant-AuthSource: YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Aug 2025 14:27:24.1354 (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: qX6icyZrkyKRNfnP2n9p6PxPerwuAWfcxTfxXVt8UAKHVxXD3HzL4N4gq7v18j+BnSbv1QFn1whIqPZL7q/gwdemTRtKvhF5hXlpNOEE9KM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: YT1PR01MB9132 On 2025-08-17 17:23, Thomas Gleixner wrote: > On Thu, Aug 14 2025 at 00:08, Thomas Gleixner wrote: >> On Wed, Aug 13 2025 at 15:36, Jens Axboe wrote: >>> On 8/13/25 3:32 PM, Thomas Gleixner wrote: >>>> Could you give it a test ride to see whether this makes a difference in >>>> your environment? >>> >>> Yep, I'll give a spin. >> >> Appreciated. > > Please do not use the git branch I had in the cover letter. I did some > more analysis of this and it's even worse than I thought. Use > > git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git rseq/wip > > instead. > > I've rewritten the whole pile by now and made it a real fast path > without the TIF_NOTIFY horror show, unless the fast path, which runs > _after_ the TIF work loop faults. So far that happens once for each > fork() as that has to fault in the copy of the user space rseq region. > OK. I'll stop reviewing this version of the series and wait for an updated version. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com