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Mon, 10 Aug 2026 05:25:10 +0000 Message-ID: <81824b51-7407-465a-b3c7-9e39d1523be3@intel.com> Date: Mon, 10 Aug 2026 13:24:59 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2] arm,x86,fs/resctrl: Generic schema description Proof of Concept To: Fenghua Yu CC: Borislav Petkov , Thomas Gleixner , "Dave Hansen" , Peter Newman , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , Dave Martin , "James Morse" , Tony Luck , Ben Horgan , Babu Moger , Drew Fustini , Reinette Chatre , "chen.yu@linux.dev" References: 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: KU3P306CA0005.MYSP306.PROD.OUTLOOK.COM (2603:1096:d10:15::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_|DS0PR11MB8183:EE_ X-MS-Office365-Filtering-Correlation-Id: 7c75afe2-bead-4243-47f1-08def69fbf51 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016|23010399003|22082099003|18002099003|11063799006|56012099006|4143699003|10067099003; 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>>> }; >>> >>> Does this mean a legacy resctrl control can be emulated by a few >>> resctrl controls (which is stored in the list)? >>> >>> e.g. legacy MB control can be emulated by a few controls? I thought >>> "MB:" line is emulated by only one native control. e.g. "MB:" line is >>> emulated by "MB_NODE:" line. >>> >> >> If I understand correctly, for region-aware RDT, the legacy MB control >> may >> be emulated collectively by region0_control, region1_control, ..., >> regionN_control. >> In the original definition, MB represents the traffic that misses the >> L3 cache and >> is refilled from all sources, which could include DRAM (region0), CXL >> (region1), >> and others. > I may misunderstand "emulation" concept here. > > I was thinking emulation mode is for backward compatibility, i.e. a Yes, this is also my understanding. > native MB control is emulating "MB:" line: writing and reading both > lines are same. So legacy user app won't be broken on new control. For legacy MB, it is currently percentage-based with a valid range of [1, 100]. Userspace might still want to write using percentage-based values to maintain backward compatibility. The native MB control, on the other hand, may have a valid range of [1, 255]. Therefore, a mapping is required to convert user-provided[1, 100] to [1, 255] before writing to the underlying hardware. > > For a list of resctrl controls (region0_control, region1_control, etc), > which one is for legacy "MB:" control so that reading/wring the control > is same as writing/reading "MB:"line? > My understanding is that all of them will be written to the same value, which has been mapped from [1, 100] to [1, 255]. According to the change: https://git.kernel.org/pub/scm/linux/kernel/git/reinette/linux.git/commit/?h=resctrl/controls_rfc_v2.1&id=2b4fa1beb03848555090a4e8a3d2bb80524e0478 list_for_each_entry(em_ctrl, &ctrl->emulated_by, entry) { //every domain for each emulating controller will write the same value } thanks, Chenyu