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Fri, 11 Sep 2026 00:06:46 +0000 Date: Thu, 10 Sep 2026 17:06:44 -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 , David E Box , , Christoph Hellwig , , Subject: Re: [PATCH v11 01/23] x86/resctrl: Give better names to X86_FEATURE flags for monitoring Message-ID: References: <20260831174421.13921-1-tony.luck@intel.com> <20260831174421.13921-2-tony.luck@intel.com> <2a814a14-2717-4363-838a-6585557baf1a@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <2a814a14-2717-4363-838a-6585557baf1a@intel.com> X-ClientProxiedBy: SJ0PR05CA0040.namprd05.prod.outlook.com (2603:10b6:a03:33f::15) 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_|PH7PR11MB7497:EE_ X-MS-Office365-Filtering-Correlation-Id: 0385e904-a67b-4c44-49e7-08df0f9891aa X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|23010399003|1800799024|376014|7416014|10067099003|6133799003|3023799007|22082099003|18002099003|56012099006|4143699003|11063799006; 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Considering that, the short description could mention > resctrl instead, for example: > x86/cpufeatures: Give better names to flags used by resctrl > > Although, I do have a question about one rename and depending on that > outcome the subject could be made more specific. > > On 8/31/26 10:43 AM, Tony Luck wrote: > > The feature flags for enumeration of Resource Director Technology (RDT) > > capabilities were chosen when the only feature was LLC cache occupancy > > monitoring and they were given names using the abbreviation CQM for > > Cache Quality of Service Monitoring. > > > > Additional monitoring features have been added to CPUs and the names > > are now more likely to confuse than inform the purpose of these flags. > > > > Rename X86_FEATURE_CQM to X86_FEATURE_RDT_M (to match the Intel Software > > Developer's Manual, and for symmetry with X86_FEATURE_RDT_A). > > > > Rename X86_FEATURE_CQM_LLC to X86_FEATURE_L3_MON since it enumerates > > that some L3 monitoring features may be present. > > Considering LLC as synonym for L3 it is not obvious why this rename is needed > (more below). I'm concerned about the "CQM" string in the name. This stands for "Cache QoS Monitoring" according to the original commit that added it: cbc82b172638 ("x86: Add support for Intel Cache QoS Monitoring (CQM) detection") This made perfect sense when the only feature was LLC cache occupancy. That's very clearly a useful metric for anyone interested in cache quality of service. But the next two monitoring features added to CPUID leaf 0xF subleaf 0x1 were memory bandwidth monitoring of local & total traffic. These are only peripherally connected to cache quality of service. I realize that this argument is somewhat undercut by the Linux naming of those features with CQM substrings: #define X86_FEATURE_CQM_MBM_TOTAL (11*32+ 2) /* "cqm_mbm_total" LLC Total MBM monitoring */ #define X86_FEATURE_CQM_MBM_LOCAL (11*32+ 3) /* "cqm_mbm_local" LLC Local MBM monitoring */ But those seem wrong too. > > > > Add missing dependency to cpuid_deps[]. > > nit: dependency -> dependencies > > > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h > > index f70ee74b5f92..6a7f0adb123e 100644 > > --- a/arch/x86/include/asm/cpufeatures.h > > +++ b/arch/x86/include/asm/cpufeatures.h > > ... > > > @@ -285,7 +285,7 @@ > > * > > * Reuse free bits when adding new feature flags! > > */ > > -#define X86_FEATURE_CQM_LLC (11*32+ 0) /* "cqm_llc" LLC QoS if 1 */ > > +#define X86_FEATURE_L3_MON (11*32+ 0) /* "cqm_llc" LLC QoS if 1 */ > > The original name matched the description and since the description needed no changing it > is not clear why the feature name needed to change? I do see some redundancy in the name with > "LLC" as well "cache" making an appearance, but none of that is inaccurate, is it? The changelog > claims that the name confuses the purpose. How does X86_FEATURE_CQM_LLC confuse the purpose of > the flag? See above ... > > > #define X86_FEATURE_CQM_OCCUP_LLC (11*32+ 1) /* "cqm_occup_llc" LLC occupancy monitoring */ > > #define X86_FEATURE_CQM_MBM_TOTAL (11*32+ 2) /* "cqm_mbm_total" LLC Total MBM monitoring */ > > #define X86_FEATURE_CQM_MBM_LOCAL (11*32+ 3) /* "cqm_mbm_local" LLC Local MBM monitoring */ > Reinette > -Tony