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Thu, 10 Sep 2026 03:52:41 +0000 Message-ID: Date: Wed, 9 Sep 2026 20:52:39 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 02/23] x86/resctrl: Check if monitoring features are enabled To: Tony Luck , Fenghua Yu , "Maciej Wieczor-Retman" , Peter Newman , James Morse , Babu Moger , Drew Fustini , Dave Martin , Chen Yu , David E Box , CC: Christoph Hellwig , , References: <20260831174421.13921-1-tony.luck@intel.com> <20260831174421.13921-3-tony.luck@intel.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: <20260831174421.13921-3-tony.luck@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0274.namprd04.prod.outlook.com (2603:10b6:303:89::9) 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_|SA3PR11MB8073:EE_ X-MS-Office365-Filtering-Correlation-Id: d19e983e-d62e-4864-3f94-08df0eeef668 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|366016|23010399003|11063799006|56012099006|4143699003|10067099003|921020|6133799003|18002099003|22082099003; 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There goes the promise that the available AI tools means reviewers only need to focus on what matters :() To support this change above could perhaps be expanded with "... which in turn is gated by X86_FEATURE_RDT_M." > > Add check feature bits. This sentence does not sound right. How about something like "Add checks for these feature bits."? > > Fixes: cbc82b172638 ("x86: Add support for Intel Cache QoS Monitoring (CQM) detection") > Signed-off-by: Tony Luck ... > diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c > index 2435eddd24eb..fcbecf677914 100644 > --- a/arch/x86/kernel/cpu/resctrl/core.c > +++ b/arch/x86/kernel/cpu/resctrl/core.c > @@ -968,20 +968,27 @@ static __init bool get_rdt_mon_resources(void) > struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl; > bool ret = false; > > - if (rdt_cpu_has(X86_FEATURE_CQM_OCCUP_LLC)) { > - resctrl_enable_mon_event(QOS_L3_OCCUP_EVENT_ID, false, 0, NULL); > - ret = true; > - } > - if (rdt_cpu_has(X86_FEATURE_CQM_MBM_TOTAL)) { > - resctrl_enable_mon_event(QOS_L3_MBM_TOTAL_EVENT_ID, false, 0, NULL); > - ret = true; > - } > - if (rdt_cpu_has(X86_FEATURE_CQM_MBM_LOCAL)) { > - resctrl_enable_mon_event(QOS_L3_MBM_LOCAL_EVENT_ID, false, 0, NULL); > - ret = true; > + /* Any monitoring at all? */ > + if (!cpu_feature_enabled(X86_FEATURE_RDT_M)) Previous patch aimed for "symmetry with X86_FEATURE_RDT_A" ... but the "symmetrical" code in get_rdt_alloc_resources() is: if (!boot_cpu_has(X86_FEATURE_RDT_A)) return false; Why is enumeration of these feature bits done differently (cpu_feature_enabled() vs boot_cpu_has())? > + return false; > + > + /* Any of the L3 monitoring features? */ > + if (cpu_feature_enabled(X86_FEATURE_L3_MON)) { Could this reduce indentation and churn by negating the check? Patch #12 and #13 seem to build on the flow introduced here so my comments about this function are split between these patches. > + if (rdt_cpu_has(X86_FEATURE_CQM_OCCUP_LLC)) { > + resctrl_enable_mon_event(QOS_L3_OCCUP_EVENT_ID, false, 0, NULL); > + ret = true; > + } > + if (rdt_cpu_has(X86_FEATURE_CQM_MBM_TOTAL)) { > + resctrl_enable_mon_event(QOS_L3_MBM_TOTAL_EVENT_ID, false, 0, NULL); > + ret = true; > + } > + if (rdt_cpu_has(X86_FEATURE_CQM_MBM_LOCAL)) { > + resctrl_enable_mon_event(QOS_L3_MBM_LOCAL_EVENT_ID, false, 0, NULL); > + ret = true; > + } > + if (rdt_cpu_has(X86_FEATURE_ABMC)) > + ret = true; > } > - if (rdt_cpu_has(X86_FEATURE_ABMC)) > - ret = true; > > if (!ret) > return false; In further support of above suggestion the code below calls rdt_get_l3_mon_config(), the enumeration depending on X86_FEATURE_L3_MON, outside the block where this feature bit is confirmed to be set. Reinette