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Fri, 21 Aug 2026 19:44:10 +0000 Date: Fri, 21 Aug 2026 12:44:08 -0700 From: "Luck, Tony" To: Reinette Chatre CC: Fenghua Yu , Maciej Wieczor-Retman , Peter Newman , James Morse , Babu Moger , "Drew Fustini" , Dave Martin , Chen Yu , , , Subject: Re: [RFC PATCH 1/4] x86/resctrl: Check if monitoring features are enabled Message-ID: References: <20260819161323.11587-1-tony.luck@intel.com> <20260819161323.11587-2-tony.luck@intel.com> <9787f9de-c72d-4c0d-b9a9-867b0f4377f5@intel.com> Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9787f9de-c72d-4c0d-b9a9-867b0f4377f5@intel.com> X-ClientProxiedBy: BY3PR04CA0017.namprd04.prod.outlook.com (2603:10b6:a03:217::22) To SJ1PR11MB6083.namprd11.prod.outlook.com (2603:10b6:a03:48a::9) 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: SJ1PR11MB6083:EE_|LV8PR11MB8723:EE_ X-MS-Office365-Filtering-Correlation-Id: ee8e38e9-2e23-4796-0c68-08deffbc9223 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|23010399003|1800799024|6133799003|22082099003|18002099003|3023799007|56012099006|4143699003|10067099003|11063799006; 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> > bool ret = false; > > > > + if (!cpu_feature_enabled(X86_FEATURE_CQM)) > > + return false; > > Is this missing a check of X86_FEATURE_CQM_LLC also? > > As I understand resctrl learns from X86_FEATURE_CQM whether the system supports > resource monitoring in general. Contrary to what the feature name suggests, there is > another step needed to determine which resource(s) support monitoring via > CPUID(0xF,0x0).EDX where bit 1 indicates LLC monitoring that needs to be set before > the LLC resource-specific monitoring properties can/should be determined. Yes. Missing that check. I agree that the feature define names are bad. To avoid continued confusion I should rename the #defines to match the bit names in the Intel SDM (but leaving the /proc/cpuinfo visible strings at "cqm" and "cqm_llc" as those are user ABI now). X86_FEATURE_CQM -> X86_FEATURE_RDT_M X86_FEATURE_CQM_LLC -> X86_FEATURE_L3_MON > > Apart from the checks here I see that cpuid_deps[] accurately reflects the relationship > between X86_FEATURE_CQM_LLC and the different LLC monitoring features checked for below. > I do not see cpuid_deps[] capturing the relationship between X86_FEATURE_CQM and > X86_FEATURE_CQM_LLC though. Could adding it complete the handling of relationships between > these leaves? Yes. > > Similarly I think cpuid_deps[] may be missing X86_FEATURE_ABMC's dependency on > X86_FEATURE_CQM_LLC. Maybe no? X86_FEATURE_ABMC isn't enumerated in CPUID(0xF,*). It comes from the AMD CPUID(0x80000020,0)EBX{5} Babu: The AMD architecture programmer's manual just says: "Support for ABMC is identified by CPUID Fn8000_0020_EBX_x0[ABMC] (bit 5) being set. If ABMC is supported, the feature’s attributes and capabilities are enumerated by CPUID Fn8000_0020_x5 as detailed in Appendix E of APM volume 3" It isn't explicitly stated whether this depends on CPUID Fn0000_000F_x0 EDX{1}, which AMD names: "L3CacheMon - L3 monitoring capability" > > + > > if (rdt_cpu_has(X86_FEATURE_CQM_OCCUP_LLC)) { > > resctrl_enable_mon_event(QOS_L3_OCCUP_EVENT_ID, false, 0, NULL); > > ret = true; > > Reinette -Tony