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Wed, 10 Jun 2026 18:05:44 +0000 Message-ID: <83ea86f6-cc2c-47ca-88fa-41a510a73d25@intel.com> Date: Thu, 11 Jun 2026 02:05:35 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] mpam,x86,fs/resctrl: Generic schema description Proof of Concept To: Reinette Chatre CC: Borislav Petkov , Thomas Gleixner , "Dave Hansen" , Peter Newman , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , Ben Horgan , Tony Luck , Dave Martin , James Morse , Drew Fustini , Babu Moger , Fenghua Yu References: <29c95b69-e1a4-46b1-ab8b-45c09308b924@arm.com> <7f2d0cc3-266c-4fa3-a9ba-7352325c76d1@intel.com> <3ef279c9-c4b3-48cb-8235-da8a871b54f9@arm.com> <5cffdb88-924e-43e7-84f2-ea19d82910fb@intel.com> <0c957e0a-0188-40c0-96e6-4e5d787a8ae6@arm.com> <8bd94a5f-1460-4bc3-a2b2-68a298200ad8@intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: TPYP295CA0019.TWNP295.PROD.OUTLOOK.COM (2603:1096:7d0:a::14) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) 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: DM4PR11MB6020:EE_|DM4PR11MB7758:EE_ X-MS-Office365-Filtering-Correlation-Id: a3937df4-1d44-472a-7dff-08dec71ae426 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|7416014|376014|366016|22082099003|18002099003|11063799006|4143699003|5023799004|56012099006|3023799007; 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First, when we refer to the "legacy" for region-aware >> RDT, I suppose it corresponds to "MSR access" plus "percentage-based control". >> >> case 1: >> If the platform does not support region-aware RDT (no ERDT table is detected), >> the MB is naturally the "legacy" MB, and the info directory would look like: >> >> info >> └── MB >>         └── resource_schemata >>                 └── MB >> >> case 2:If the platform supports region-aware RDT (i.e., ERDT parsing succeeds), >> then the structure looks like below: >> >> info >> └── MB >>         └── resource_schema >>                 └── MB                  <=== legacy >>                 └── MB_REGION0_OPT >>                 └── MB_REGION1_OPT >>                 └── MB_REGION0_MIN >>                 └── MB_REGION1_MIX >>                 └── MB_REGION0_MAX >>                 └── MB_REGION1_MAX >> >> The OS supports runtime switching between the legacy MB and >> region-aware MB, via a MB scope control like: >> /sys/fs/resctrl/info/MB/resource_schemata/mode >> [legacy] native >> If the user wants to use the legacy interface, the system >> will fall back to the default [MSR-based, percentage]; if the >> user wants to use the new interface, the region-aware interfaces >> will be used. Since the two modes are mutually exclusive, there >> seems to be no need to use MB_REGION0_MAX to emulate legacy MB. > > - This implies that all current and future ERDT capable systems will keep > supporting MSR access with the legacy "percentage based control". Is this > accurate? I don't know the answer for now; it may depend on how the hardware maintains backward compatibility. Let me have a check. > What will behavior be on an ERDT system that does not support > MSR access with the percentage-based control? Then in this case, we may need to emulate the legacy MBA if users do not wish to switch to the new interface. > - It is not obvious to me what you plan to have as default interface - > I believe this should be "legacy" interface to ensure this will not > break user space. resctrl should only switch to "native" after user > demonstrates (by switching) familiarity with the new interface. > Yes, setting "legacy" as the default will accommodate users who rely on the old interfaces. > Reinette > > >