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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> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20251028083356.cDl403Q9@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: SA2PEPF00001505:EE_|PH7PR12MB9175:EE_ X-MS-Office365-Filtering-Correlation-Id: 5fa4b299-fe0c-49ba-213b-08de15ff331c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|7416014|376014|36860700013|1800799024; X-Microsoft-Antispam-Message-Info: =?utf-8?B?YnU1U1RwaGNOVTZMYkRMa01SMjVLZ0VKT1B0TFFCbkNRK3NzdUxpbDNMbnJi?= =?utf-8?B?T3pIRWFtM2k1TkpBN2hIdklza0UrMFdmRk1pR09PdXhkblhKSlBsMndLSmVI?= =?utf-8?B?YTUwZVhpZFlqUVJSK2xCaFQzMktxelREOWtJQktPUW5CcTRPSVRKdUl0ZzZS?= =?utf-8?B?RCtlUFR6TDRQVVdTZUo5clpXaXRXUlQxRU1BeEFUTkN6QTFyQVZYbWdhWjYw?= =?utf-8?B?VG9EdjROSGd6cWJhQStLOVAxdnJ5MElCdG1WRW1mQTRFdG1mUGFKMGp1MzQ4?= =?utf-8?B?RWdEMnRRbXdrV1hiRlpZTVZuaWk4VE05ZmJyUmRuaE0vNzhpMkQrQXcwZnJU?= =?utf-8?B?R3Fyd0JJTVNncjhsUktobkQ4Y2wrTEZtSjdzRFdyVC9ZV3VaaVNHLzR2MnRN?= =?utf-8?B?cW1YU0RtamNxZnpoVmo1WHhLSjZxWGFNcVRXL01nNG14VFh4MWJwSDdLdkdE?= =?utf-8?B?TDBwSDh1b0hLVHNoZXR1NUN6cGFqMVBZOFBzRS9Cd2xNckhTYmFhZG5MdTJW?= =?utf-8?B?TitsSCtmNHZ2UDJneU5DanIxSmsydmpvRUJtazlSYksrckVFTkNXL3E0WUJv?= =?utf-8?B?RE05SmE4eCtBUjRuR1hHS3pZVmlqcHJCcDF3d3pKcjBPdmV1endCRDB2U1g5?= =?utf-8?B?bzFXdTB1WS9Jc05QQlFWMlZKOG1HcjV0Y1hhMC9ZNk5sMENpSkVnSjcyY1hE?= =?utf-8?B?YWpNendPNXJ1Wmpld3MyUXpaR2dRYkN1d0pFa0JsUy9QeU1od043SjJtL2Qx?= =?utf-8?B?Uy94M0RCTGFuTEI3T1dkM2NIVlRDOGJBbEFYZXRHRWthSXNJZWdESFMrRmpn?= =?utf-8?B?Mk1vNmZqbTdSK25nN0U0Y1ZDb01jQ1BLc2UrWExUc0JyZFhWZzVuWjAvczZ6?= =?utf-8?B?QitFY0VKL0IrK3BpK295TDRvZDgramtjdVNDNmdSZTlGdkdESUpsRzZrZnJ2?= =?utf-8?B?bWtzbUQxRXBmcHVBMmJSZldWSG1CMUhpMEhnMUR1UUNNR1hra0w2V0pWTm45?= =?utf-8?B?WHRiSlFrcXFWTDFNbDJBL0FSbkVJYlFpUXU5R2QzOTFSSEtOR3d1b3BGNTR6?= =?utf-8?B?MHJSUXRtZU1aMUUvckpVSk9ub2s4eEtCMkZUZlMybFBwbmdsNVRNSFk3WWkx?= =?utf-8?B?VUpZRHZFMXJkUkF6ZlVnOWpvek1YUHhOem1UVWNmKzk0Z2tYQjFuOXJZTDVx?= =?utf-8?B?elBjVExlc2NRVWNHcEJGYjlEZTJXQXV5MXlLYVR6SVFSeVhTUWU0aUlCbnVY?= =?utf-8?B?VTR5OUcwbmFFK2tKMThjbEVRTmdpWTkvOStTcGhhWmJ0V1RQL05kN1NCR1ZV?= =?utf-8?B?YmNxQ0JlWi9jTEtkS29uNHZ0V2U4Q05WNytnZ3hHalRDTnVldHovWEo0enBL?= =?utf-8?B?TkZZU3BLNlQ2NEhRUEd5ekgwYkFuTWhOeGFLVUlYNXgxRHR5clBNb1pwaVZ4?= =?utf-8?B?a2tUVnEyOXc2ZDEzMVh2cGlCUmZSdlNGSjJQZGd6Rm1hQ1dhTGMvbVNEakt3?= =?utf-8?B?TUlmMFkrVFh2Z1dJSG1sRTJDcm00ajRldnFUWEpsT2lYcVQ1NGhNdUo4VU5S?= =?utf-8?B?VXNGQm1HMlAzekRNZG1MTDhSYVZzdTJQWXlabVZJbHBaN3hrcjhBOVdFUmEr?= =?utf-8?B?L2ptVzdkMlppVmxFcnhIZnowaXF2eGxKMUdoa05RYTIya1NBVTJxTzREWTVT?= =?utf-8?B?NWY1aDVrcWlGSzFjdU9MZzdodnRXQ3lNaVE0dGdtUWwrUTgyaUFzU1BEYzFt?= =?utf-8?B?ZSswS0o3Rk4rekppRmdHVm1EWjkxS0pBOVNmYTFnNkFEL28wb1FYN1ZkS0F2?= =?utf-8?B?MmZVSGpVdTRzOHhDUlhobW1DbS8wemNTODE4VGxVdTA5WUJzaWJiWTZjU2pM?= =?utf-8?B?dlc0VnExajk1MWg1WDZhRGkvQkdVZzhQdjlrQ2kxTWg2bW9PQmtlQ01kdDAv?= =?utf-8?B?UXppd3dqSHpUdURpMmxJMXhrVERCaGN4bytRTXV4QXNjeXQyRmdIbDJpcUxn?= =?utf-8?B?OVBjemlVVGtyN201ZWRZK2FXcnFIWm1oT2ovMThlVUQ1UWJzV0pkMVY4SDFJ?= =?utf-8?B?UkZMRUlvQ2s2cVdSTW1jeWlnYzRVaHZDWDVzL1UvVFE0d0ZQVTAxZlJIRGVk?= =?utf-8?Q?qqAg=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)(82310400026)(7416014)(376014)(36860700013)(1800799024);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Oct 2025 08:51:35.0904 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5fa4b299-fe0c-49ba-213b-08de15ff331c 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: SA2PEPF00001505.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB9175 Hello Sebastian, On 10/28/2025 2:03 PM, Sebastian Andrzej Siewior wrote: > On 2025-10-27 17:26:29 [+0100], Thomas Gleixner wrote: >> On Mon, Oct 27 2025 at 12:38, Sebastian Andrzej Siewior wrote: >>> On 2025-10-22 14:57:38 [+0200], Thomas Gleixner wrote: >>>> +static enum hrtimer_restart rseq_slice_expired(struct hrtimer *tmr) >>>> +{ >>>> + struct slice_timer *st = container_of(tmr, struct slice_timer, timer); >>>> + >>>> + if (st->cookie == current && current->rseq.slice.state.granted) { >>>> + rseq_stat_inc(rseq_stats.s_expired); >>>> + set_need_resched_current(); >>>> + } >>> >>> You arm the timer while leaving to userland. Once in userland the task >>> can be migrated to another CPU. Once migrated, this CPU can host another >>> task while the timer fires and does nothing. >> >> That's inevitable. If the scheduler decides to do that then there is >> nothing which can be done about it and that's why the cookie pointer >> exists. > > 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. As for overstepping the limits on the previous CPU, the EEVDF algorithm (using the task's "vlag" - the vruntime deviation from the "avg_vruntime") would penalize it accordingly when enqueued. The previous CPU would just get a spurious interrupt and since the timer cookie doesn't match with "current", the handler does nothing and goes away. -- Thanks and Regards, Prateek