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Thu, 20 Jun 2024 22:49:28 +0000 Message-ID: <622f93e6-14df-4718-abb2-33eaa5d160fe@intel.com> Date: Thu, 20 Jun 2024 15:49:23 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 00/19] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC) To: , , , , , , CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , References: <2e488812-671e-4aa9-a292-c54b174f2dd7@intel.com> <6e297b6e-e39b-e358-7bb5-59add62f8b2b@amd.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: <6e297b6e-e39b-e358-7bb5-59add62f8b2b@amd.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MW4PR04CA0190.namprd04.prod.outlook.com (2603:10b6:303:86::15) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ2PR11MB7573:EE_|MN0PR11MB6157:EE_ X-MS-Office365-Filtering-Correlation-Id: 1eed7408-78bf-41ee-9569-08dc917b3d91 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230037|1800799021|7416011|376011|366013; 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According to the docs the counters >> will return "Unavailable" right after reconfigure so it seems that there >> are scenarios where an "assigned" counter returns "Unavailable". It seems >> more >> useful to return "Unassigned" that will have a new specific meaning that >> overloading existing "Unavailable" that has original meaning of "try >> again" .... >> but in this case trying again will be futile. > > Hardware returns "Unavailable" in both the cases. So, thought of reporting the same without any interpretation. > I do not see these as the same. When a counter is assigned and its read returns "Unavailable" then the user reasonably expects that retry will work. When a counter is not assigned then no amount of retries will result in data. How is user space expected to distinguish between the two scenarios that return the same error with such significantly different meaning? rdtgroup_mondata_shows() can just peek into the monitor group state and see if a counter is assigned and immediately return "Unassigned" if no counter is assigned, no? I see no need for it to IPI another CPU and try to read a counter that it already knows will be futile. This seems unnecessary and the generic "Unavailable" is not helpful to user space. Reinette