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Fri, 7 Aug 2026 15:35:34 +0000 Message-ID: Date: Fri, 7 Aug 2026 08:35:31 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2] arm,x86,fs/resctrl: Generic schema description Proof of Concept To: "Moger, Babu" , "Luck, Tony" CC: Ben Horgan , James Morse , "Dave Martin" , Babu Moger , Drew Fustini , Fenghua Yu , Chen Yu , Borislav Petkov , Thomas Gleixner , Dave Hansen , Peter Newman , "x86@kernel.org" , "linux-kernel@vger.kernel.org" References: <7a8b6cc8-d194-4af2-9fb9-2438d2dcae01@intel.com> <9d0239e6-318e-4a59-937d-a64b839e02e9@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: MW4PR04CA0350.namprd04.prod.outlook.com (2603:10b6:303:8a::25) 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_|MN0PR11MB6229:EE_ X-MS-Office365-Filtering-Correlation-Id: 11ddcaa1-8be0-450c-1433-08def499855d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|366016|1800799024|376014|7416014|22082099003|18002099003|3023799007|56012099006|4143699003|11063799006|10067099003|6133799003; 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>>>>>                  mpam_ctrl->r_ctrl.name = RESCTRL_CTRL_NAME_DEF; >>>>> +               INIT_LIST_HEAD(&mpam_ctrl->r_ctrl.emulated_by); >>>>>                  INIT_LIST_HEAD_RCU(&mpam_ctrl->r_ctrl.domains); >>>>>                  __set_bit(RESCTRL_BITMAP_FLAG_SPARSE, mpam_ctrl->r_ctrl.bitmap.flags); >>>>>                  mpam_ctrl->r_ctrl.bitmap.cbm_len = class->props.cpbm_wd; >>>>> @@ -1048,6 +1049,7 @@ static int mpam_resctrl_control_init(struct mpam_resctrl_res *res) >>>>>                  r->ctrl_scope = RESCTRL_L3_CACHE; >>>>>                  mpam_ctrl->r_ctrl.type = RESCTRL_CTRL_SCALAR; >>>>>                  mpam_ctrl->r_ctrl.name = RESCTRL_CTRL_NAME_DEF; >>>>> +               INIT_LIST_HEAD(&mpam_ctrl->r_ctrl.emulated_by); >>>>>                  INIT_LIST_HEAD_RCU(&mpam_ctrl->r_ctrl.domains); >>>>> >>>>>                  r->bw_throttle_mode = THREAD_THROTTLE_UNDEFINED; >>>> >>>> Thank you for this. Added this and it is now available in branch resctrl/controls_rfc_v2.1 >>> >>> Is same needed for x86? I don't see any initialization of the >>> "r_ctrl.emulated_by" lists in similar initialization functions. >> x86 "emulated_by" list initialization should be in both branches. >> >> Branch resctrl/controls_rfc_v2.1 combined all "emulated_by" list initialization >> (for x86 and MPAM) into commit: >> 3407e523c988 ("fs/resctrl: Introduce emulated controls and control mode") >> >> In the original resctrl/controls_rfc_v2 the x86 "emulated_by" list initialization can >> be found in commit fbed64f80515 ("x86/resctrl: SAMPLE: Emulated controls") >> > > Looking at the commit: > > commit 3407e523c988 ("fs/resctrl: Introduce emulated controls and control mode") > > Based on the patch description, emulated controls are intended to be > used only when there is a difference between the native and legacy > controls. If no such difference exists, both modes should operate > identically. The original AMD MBA enabling did not follow the original percentage based MBA control so resctrl essentially has *two* "legacy" MB controls today: one for AMD and one for Intel, MPAM, and RISC-V (planned afaik). That cannot be changed now. AMD would continue to expose the MB control that is not the percentage based "legacy" control but actually AMD's native control. In short, yes, on AMD's "MB" control the "legacy" and "native" control modes should operate identically. At least now users could use the files in info/MB/schemata/MB/* to learn the properties of the control. > For MBA(AMD) and GMBA, there does not appear to be any difference > between the two modes. Is that understanding correct? It is not clear to me how resctrl should support AMD's GLBE. Note I am intentionally not using GMBA since that already makes an assumption on how resctrl will support this. Do you perhaps have an answer for Ben's question in https://lore.kernel.org/lkml/1444b515-752e-4167-87f5-30ace189e05c@arm.com/ ? GLBE claims to enable users to allocate memory bandwidth at node scope but the memory is managed at L3. This results in scenarios where, for example, a NUMA node can be online and used but resctrl cannot expose it for bandwidth allocation when all the CPUs at that NUMA node scope are offline. GLBE is thus not actually allocating memory bandwidth at the NUMA node. Should resctrl prepare for some future where an AMD system may support memory bandwidth allocation at the NUMA node while also supporting GLBE (memory bandwidth allocation at L3)? Reinette