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Wed, 16 Sep 2026 16:26:35 +0000 Date: Wed, 16 Sep 2026 09:26:33 -0700 From: "Luck, Tony" To: Reinette Chatre CC: Fenghua Yu , Maciej Wieczor-Retman , Peter Newman , James Morse , Babu Moger , "Drew Fustini" , Dave Martin , Chen Yu , David E Box , , Christoph Hellwig , , Subject: Re: [PATCH v11 19/23] x86/resctrl: Export interface to report telemetry unbind/remove Message-ID: References: <20260831174421.13921-1-tony.luck@intel.com> <20260831174421.13921-20-tony.luck@intel.com> <1a418996-fe0a-4553-bd21-9881ab182e51@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1a418996-fe0a-4553-bd21-9881ab182e51@intel.com> X-ClientProxiedBy: SJ0PR05CA0176.namprd05.prod.outlook.com (2603:10b6:a03:339::31) To SJ1PR11MB6083.namprd11.prod.outlook.com (2603:10b6:a03:48a::9) 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: SJ1PR11MB6083:EE_|IA1PR11MB6514:EE_ X-MS-Office365-Filtering-Correlation-Id: bf1a85d0-f3b9-4373-004e-08df140f4672 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016|23010399003|56012099006|18002099003|22082099003|4143699003|10067099003|11063799006; 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> > u32 idx; > > > > + guard(mutex)(&aet_register_lock); > > + > > hmmm ... this means that reading an event can sleep now ... but it is still > possible to call this via IPI (smp_call_function_any()) if the CPU is part > of the nohz_full subset? All AET events are implemented with counters in MMIO space and can be read from any CPU. So this check in mon_event_read() bypasses the check for nohz CPUs: if (evt->any_cpu) { mon_event_count(rr); goto out_ctx_free; } But even if it didn't, is there some prohibition for nohz CPUs to sleep? I can see possible issues with a timed delay that might rely on a clock tick to wake. But it would seem that any read(2) system call from a regular file might sleep waiting for I/O completion. > > pevt0 = pevt - pevt->idx; > > e = container_of(pevt0, struct event_group, evts); > > idx = rmid * e->num_events; > > Reinette -Tony