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Fri, 25 Sep 2026 14:37:22 +0000 Message-ID: <110d2c7f-8354-4d25-aff8-cd5ceb46334b@intel.com> Date: Fri, 25 Sep 2026 07:37:20 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 15/25] x86,fs/resctrl: Handle systems where AET is the only resource To: "Luck, Tony" CC: Fenghua Yu , Maciej Wieczor-Retman , Peter Newman , James Morse , Babu Moger , "Drew Fustini" , Dave Martin , Chen Yu , David E Box , , Christoph Hellwig , , References: <20260916231320.14502-1-tony.luck@intel.com> <20260916231320.14502-16-tony.luck@intel.com> <39582d24-0fc1-4d5e-bc05-01c2f29ddfb1@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: MW4PR03CA0234.namprd03.prod.outlook.com (2603:10b6:303:b9::29) To SJ2PR11MB8370.namprd11.prod.outlook.com (2603:10b6:a03:540::20) 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: SJ2PR11MB8370:EE_|CO1PR11MB5043:EE_ X-MS-Office365-Filtering-Correlation-Id: 1fb20713-9cd5-4513-88e0-08df1b1282a9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014|23010399003|10067099003|11063799006|56012099006|4143699003|18002099003|22082099003; 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>>> + goto skip_l3_feature_checks; >> >> This goto looks unnecessary. Why not just "return true"? Even so, this >> also changes behavior from the previous version in a way that is not clear >> to me. I was expecting this to consider the number of RMIDs supported by the system, >> now that this function added: >> >> pqr_assoc_num_rmid = cpuid_ebx(0xf) + 1; >> >> Should this be: >> >> if (!cpu_feature_enabled(X86_FEATURE_CQM_LLC)) >> return pqr_assoc_num_rmid > 1; >> >> Although ... looking at this closer it does look strange for pqr_assoc_num_rmid >> to be 1, thus reflecting that the system supports one RMID, when zero may be more >> accurate? > > If X86_FEATURE_CQM_LLC is set, then monitoring is supported and the system > must support at least one RMID. I don't see a need to insist on more than one > RMID as a precondition for using resctrl. It wouldn't be super interesting My suggestion was not to use "more than one RMID as a precondition". By copying the relevant code not shown in the hunk pqr_assoc_num_rmid = cpuid_ebx(0xf) + 1; I aimed to highlight that if the system returns zero then pqr_assoc_num_rmid will contain 1. The "pqr_assoc_num_rmid > 1" is thus not a check for "more than one RMID" but instead a check that the system did not return zero. > as all activity would be captured by that single RMID. But it would be > keeping counts of events. > > So you first instinct above to "just return true" seems reasonable. > Reinette