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McKenney" , Boqun Feng , Jonathan Corbet , Prakash Sangappa , Madadi Vineeth Reddy , Steven Rostedt , Arnd Bergmann , References: <20251022110646.839870156@linutronix.de> <20251022121427.406689298@linutronix.de> <20251027113822.UfDZz0mf@linutronix.de> <87cy68wbt6.ffs@tglx> <20251028083356.cDl403Q9@linutronix.de> <20251028090015.hcvhq9YP@linutronix.de> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20251028090015.hcvhq9YP@linutronix.de> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: None (SATLEXMB05.amd.com: kprateek.nayak@amd.com does not designate permitted sender hosts) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MWH0EPF000971E8:EE_|DS0PR12MB7632:EE_ X-MS-Office365-Filtering-Correlation-Id: ce647185-4e59-4c14-d104-08de16037b38 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|82310400026|36860700013|1800799024; X-Microsoft-Antispam-Message-Info: =?utf-8?B?clhpaG5QbUphWCtxY21Za0hObmVkZW1FaVZhZHdGRWdTUFhvRHdyYmpBRXNa?= =?utf-8?B?ZnN5MmZGVlVhWnZka1A4WFB0WkZaU1V3a2xuMVVNUlBlcUsrYjU0WHlBMEF1?= =?utf-8?B?WkNNZTI1Y1U2cHNsV2swMU5ObHZUVjlpUVpiZlVmL3grT1NhR0w0TFQweDE2?= =?utf-8?B?RVZBanR3dm1xeHBPdHQySmdtTWVBTk9JbFAvRkdDWGF3T2M5VldpQWRlRnQ1?= =?utf-8?B?a1dlOWlYbERwczBZbTdsYWFDREFVSEU1ZnRETjB3SVMzVHVBdTJVakJJaGlx?= =?utf-8?B?NU1SeEtZL1pjVmVmejFiSVpvblV3aW9USW1GVkpwQTBCeGlsNGNzVUEyTE9F?= =?utf-8?B?TmZkdVRyYlNhU2RIV0NQWUUwcnNsN3paUEVhMVkvNm4wZDg4TVpzMEc1ZWRM?= =?utf-8?B?SlhqUWpYUGhtMm1HYll0QjhGTExZWEVDUG5sR1o1NXRiUzhxdTZMWklJOVFj?= =?utf-8?B?a2laWCtOdXh3d21FVlhPUU5vT3YxMTZoOW85OHRLNUx3UXRZVXBxUnQ3NkxO?= =?utf-8?B?RU5CbUNFQWxvZExJNkpTMFF3Mm02T2xTa2lnWm83WnUvdjdDY1p1Wk0wdUtD?= =?utf-8?B?anQ5eUZRYXpnWkZ0dElGaXgrN1Q1aW1EbEJQUkp4dURiSzJ5WE5PcmxFcG8x?= =?utf-8?B?OFZSTzFVYXA2bFpHZkVjWTZBcFc0RHBlUFdVdWY2ekl1WTJZUVgvS2dQNUE4?= =?utf-8?B?Ym5CbGJacnJlKzlNNVlFZjg2akRrV0JnczE1T0FjODNHcXdEWWJyQ0kwUXRi?= =?utf-8?B?QXZnYTcvQmx5MUF3SGJsME5mUGF1Y2lXZjByRUdoNDB3TXE1UmFjbmI5dW9Q?= =?utf-8?B?U3JVVXIxSEM0eGI5NU9Kc1J6ZmhlcmVyZk12NU8vYzVvVnBvRUszQjB4bDBZ?= =?utf-8?B?VHdkdStrdnBOV04yWnB1enEvLzdBR3JSV1ZndU1KWEt0WXAyZEQrSCsrZlFL?= =?utf-8?B?R1Exc3VzQkZ0Vndhd0FhNFZ5QWZFVGVzSXpobUZsdzAwblFCMWxvSjJkUll3?= =?utf-8?B?a2xicVBqV2xrSE9JMnBLdDc4YWVNMndTb3o0amZ5ZWFpQVBRaXVoNUZQbmpK?= =?utf-8?B?TEFiSU14MWpDMGJvcHB6dWZkTmVoY2ttcnl4eFpGUStIa3dCdmdOVkp0YzVW?= =?utf-8?B?dEpWMEU5UHE1TEpJaGZTUzBsRi9yaEpJd3FrSWR6bnBhcFhMaDJaZGhHRUNM?= =?utf-8?B?RzRkYzQ3QzZHd0Rpam53SThzaHpRak5yVGVDcGp4ZElXanpYZmV2MlFsTkdx?= =?utf-8?B?RmRqOHAzQUExK1U0Nnp1aEs2UEhsZURUSVdST2g3Y1UzdTNJLzl1VEUxTlFP?= =?utf-8?B?ZE85STBsS1FpLzVDNEFCRXovYzVSRWFNbE8zK3VhbE9MVXV6TGpmbExlb2Q2?= =?utf-8?B?SDY2MUVpQ2NmVEZMd0R0b0oyNWg3TVhRUExETWlub1lwWmhtNzBNQURVSVNR?= =?utf-8?B?Y1pDZjJxd3JVbkYxdVMzUVZxanc5R2ZuanY4OXlFVlJvei9JZDBpaVVhQUxX?= =?utf-8?B?Mk5mUkgwK0RwTk9JYnMzck1lOE9XcmxQN2Qzc29BdCt0V2d0NzhYWk5MUy9N?= =?utf-8?B?a1BMMFN1b3JXeXZDUmNGdkpZVGFYQXU5R2FWU2FMM3VaRGZiTUF6MkRtTDRJ?= =?utf-8?B?OERBOW5jaHpRcWViK1JJaUp2L09rcHVNcGZSYWZXN1JQVDVIbnBnOG5nd281?= =?utf-8?B?ZGwzZzgwbmRXOTdhM0JTbzBWejV3L1h0SWxHbXArVjZYL3liTW5rOW1tZHU2?= =?utf-8?B?Vm95SzEwM0xTMVExeWZudHAxRXBXdDBnSXdQQ1NRazhIR2JtRmVmc3BFZ2JZ?= =?utf-8?B?bEZLMEtUbURwbjlTVTlmOWZwenVkMy9vR1VaUWpLMS9DR2FPaXFMTE4zZ2t3?= =?utf-8?B?SkNWY2VEZnA1T244T3htR1RKa0kzOFJiQW5NVjdDK1QrQm4wZ0g4T0tLSDQz?= =?utf-8?B?Ri83Snp3UVlQMHpzQzBFcW1IUTlON1luSkpyRUlWVkpXdVF6ZnVWcmxNN051?= =?utf-8?B?S1A2bFZiQkxMYnV4WlU2bVdIdEp6ZWdrMUFUTkhySjByL2cwSVhSSzRSa2tt?= =?utf-8?B?QjFwS2FtVTlOb1VScDFWV0I1Q2pPQ2Vvb1RJTERSeENDbC9mRkJoWE5UY2xX?= =?utf-8?Q?yQ3k=3D?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:satlexmb08.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(376014)(7416014)(82310400026)(36860700013)(1800799024);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Oct 2025 09:22:13.9888 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ce647185-4e59-4c14-d104-08de16037b38 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: MWH0EPF000971E8.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB7632 On 10/28/2025 2:30 PM, Sebastian Andrzej Siewior wrote: >>> Without an interrupt on the target CPU, there is nothing stopping the >>> task from overstepping its fair share. >> >> When the task moves CPU, the rseq_exit_user_update() would clear all >> of the slice extension state before running the task again. The task >> will start off again with "rseq->slice_ctrl.request" and >> "rseq->slice_ctrl.granted" both at 0 signifying the task was >> rescheduled. > > I wasn't aware this is done once the task is in userland and then > relocated to another CPU. The exact path based on my understanding is: /* Task migrates to another CPU; Has to resume from kernel. */ __schedule() context_switch() rseq_sched_switch_event() t->rseq.event.sched_switch = true; set_tsk_thread_flag(t, TIF_RSEQ); ... exit_to_user_mode_loop() rseq_exit_to_user_mode_restart() __rseq_exit_to_user_mode_restart() /* Sees t->rseq.event.sched_switch to be true. */ rseq_exit_user_update() if (rseq_slice_extension_enabled()) unsafe_put_user(0U, &rseq->slice_ctrl.all, efault); /* Unconditionally clears all of "rseq_ctrl" */ -- Thanks and Regards, Prateek