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Tue, 11 Aug 2026 03:49:22 +0000 Message-ID: <5ecbbe3d-aa8c-409b-8963-0ee50b456814@intel.com> Date: Tue, 11 Aug 2026 11:49:12 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2] arm,x86,fs/resctrl: Generic schema description Proof of Concept To: Reinette Chatre CC: Tony Luck , Borislav Petkov , "Thomas Gleixner" , Dave Hansen , Peter Newman , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , Dave Martin , Ben Horgan , James Morse , Babu Moger , Drew Fustini , Fenghua Yu , "chen.yu@linux.dev" References: <9e38f138-7872-445d-9a11-105f9d0fa4d0@intel.com> <07a79f5f-ad39-447d-b43d-01e44c7870a2@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: SG2PR01CA0187.apcprd01.prod.exchangelabs.com (2603:1096:4:189::12) 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_|LV0PR11MB9791:EE_ X-MS-Office365-Filtering-Correlation-Id: 6bcb66f8-532b-42c0-007b-08def75b87b1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|23010399003|1800799024|366016|6133799003|56012099006|11063799006|4143699003|10067099003|22082099003|18002099003; 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The only way to support this "legacy" > user interface with region-aware hardware is to use the MSR interface, no? Yes, agreed. >> Then for the current region-aware MBA, should we add region-aware controllers >> as the same level as legacy controller, instead of adding them in legacy >> controllers' emulated_by list, since the legacy controller is not >> emulated by region-aware controllers? And we might need to introduce enable/disable >> flag per controller, which could be switched on/off when switching between >> legacy and native. > Please consider what will be required to support per-controller dynamic ("enable" vs "disable") > state: resctrl fs needs to expose interfaces that accept control changes from user space after > initialization that needs to be supported by architecture. In the current design resctrl fs expects > controllers to be set and configured at the time it starts so such change would require new locking > between resctrl fs and architecture. This complexity does not seem necessary to me since switching > between legacy and native accomplishes the same, no? > OK, agreed. > I find "region-aware controllers at the same level as legacy controller" together with > "per controller enable/disable" conflicting since it creates impression that user space can > enable/disable the controllers independently while there is a required dependency among the > different controllers based on whether hardware has region-aware MBA enabled or not. Even > here there would be a requirement to communicate to userspace which controllers could be > enabled/disabled together ... which is the same as the emulated list, no? I see. So we actually need a single option (control_mode) to switch between modes (legacy vs. native, mutually exclusive), rather than giving each controller its own independent enable/disable toggle. The emulated list is one way to implement control_mode, ensuring "legacy" and "native" are mutually exclusive. > > Also consider the future: > (a) Would it be possible to map legacy control value to region aware control value in the future? > I believe the answer is "yes". If resctrl starts by displaying the region-aware controllers > as emulating the legacy controller in info/ then the transition to support this will > be smooth. > > (b) Would MSR interface always be available? > I do not think resctrl should always assume this to be the case. Here I also find that starting > with exposing region aware controllers as emulating the legacy controller in info/ to support > a smooth transition. > > What problem(s) do you envision? > Based on this design, I don’t see any issues. So putting native controllers under the legacy controller could be a viable approach that can be extended in the future. thanks, Chenyu