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Tue, 25 Aug 2026 15:39:16 +0000 Message-ID: <64ac0eaf-c2da-4683-9859-81b46ff325e7@intel.com> Date: Tue, 25 Aug 2026 08:39:13 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 5/9] x86/resctrl: Parse ACPI CMRC table To: "Chen, Yu C" CC: , , , , , , , , , , References: <01d48e87-eade-438d-9d33-b1110b6bbfcd@intel.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MW4PR03CA0058.namprd03.prod.outlook.com (2603:10b6:303:8e::33) 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_|IA1PR11MB6122:EE_ X-MS-Office365-Filtering-Correlation-Id: f62184a2-835c-4d69-7be6-08df02bf0528 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|376014|7416014|1800799024|366016|10067099003|56012099006|11063799006|4143699003|22082099003|18002099003; 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The existing code can thus not accommodate the new values and need to >> be updated? >> > > Yes, the legacy CPUID reports it as 32 bits, while CMRC is declared as 64 bits. > > In theory, we should change the scale type from unsigned int to u64 to accommodate > both the legacy CPUID and CMRC. However, it seems unlikely that the scale would > exceed 32 bits. If the scale were 32 bits, the L3 occupancy would be at least > 2^32 − 1, which is about 4 GB. We have not yet seen platform with 4 GB of L3 cache. > So perhaps we can keep erdt_scale as unsigned int for now IMO. It sounds like you are saying that the spec you are enabling should not be using 64 bits for this value. It is unexpected to me that work on enabling of a spec adds such constraint without clear motivation. If you find that the spec is not correct then I think it would be better to have it changed there instead of building what appears to be unsupported assumptions into resctrl. Reinette