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Wed, 28 May 2025 22:21:43 +0000 Message-ID: <1d6606fd-5047-4286-ac69-0dfe4de1b844@intel.com> Date: Wed, 28 May 2025 15:21:42 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 00/29] x86/resctrl telemetry monitoring To: "Luck, Tony" CC: Fenghua Yu , Maciej Wieczor-Retman , Peter Newman , James Morse , Babu Moger , "Drew Fustini" , Dave Martin , "Anil Keshavamurthy" , Chen Yu , , , References: <20250521225049.132551-1-tony.luck@intel.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR08CA0055.namprd08.prod.outlook.com (2603:10b6:a03:117::32) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) 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: SJ2PR11MB7573:EE_|SJ2PR11MB8471:EE_ X-MS-Office365-Filtering-Correlation-Id: 56d180ab-fd0f-4555-4791-08dd9e3606cd X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014; 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Let me know if it helps cover the > gaps and ambiguities that you pointed out. > > -Tony > > > RMID based telemetry events > --------------------------- > > Each CPU on a system keeps a local count of various events. > > Every two milliseconds, or when the value of the RMID field in the > IA32_PQR_ASSOC MSR is changed, the CPU transmits all the event counts > together with the value of the RMID to a nearby OOBMSM (Out of band > management services module) device. The CPU then resets all counters and > begins counting events for the new RMID or time interval. > > The OOBMSM device sums each event count with those received from other > CPUs keeping a running total for each event for each RMID. > > The operating system can read these counts to gather a picture of > system-wide activity for each of the logged events per-RMID. > > E.g. the operating system may assign RMID 5 to all the tasks running to > perform a certain job. When it reads the core energy event counter for > RMID 5 it will see the total energy consumed by CPU cores for all tasks > in that job while running on any CPU. This is a much lower overhead > mechanism to track events per job than the typical "perf" approach > of reading counters on every context switch. > Could you please elaborate the CPU vs core distinction? If the example above is for a system with below topology (copied from Documentation/arch/x86/topology.rst): [package 0] -> [core 0] -> [thread 0] -> Linux CPU 0 -> [thread 1] -> Linux CPU 1 -> [core 1] -> [thread 0] -> Linux CPU 2 -> [thread 1] -> Linux CPU 3 In the example, RMID 5 is assigned to tasks running "a certain job", for convenience I will name it "jobA". Consider if the example is extended with RMID 6 assigned to tasks running another job, "jobB". If a jobA task is scheduled on CPU 0 and a jobB task is scheduled in CPU 1 then it may look like: [package 0] -> [core 0] -> [thread 0] -> Linux CPU 0 #RMID 5 -> [thread 1] -> Linux CPU 1 #RMID 6 -> [core 1] -> [thread 0] -> Linux CPU 2 -> [thread 1] -> Linux CPU 3 The example above states: When it reads the core energy event counter for RMID 5 it will see the total energy consumed by CPU cores for all tasks in that job while running on any CPU. With RMID 5 and RMID 6 both running on core 0, and "RMID 5 will see the total energy consumed by CPU cores", does this mean that reading RMID 5 counter will return the energy consumed by core 0 while RMID 5 is assigned to CPU 0? Since core 0 contains both CPU 0 and CPU 1, would reading RMID 5 thus return data of both RMID 5 and RMID 6 (jobA and jobB)? And vice versa, reading RMID 6 will also include energy consumed by tasks running with RMID 5? Reinette