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Thu, 4 Sep 2025 17:35:54 +0000 Message-ID: <11949172-e319-4d2e-b977-67aedeac5c1b@intel.com> Date: Thu, 4 Sep 2025 10:35:48 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v17 05/33] x86/cpufeatures: Add support for Assignable Bandwidth Monitoring Counters (ABMC) To: , , , , , , CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , References: <8f2c506c2e0bdc4ab3e4736435d683ceb5322839.1755224735.git.babu.moger@amd.com> <55dbe7ee-8e4a-4f09-b00e-8e879d8f6ad6@amd.com> Content-Language: en-US From: Reinette Chatre In-Reply-To: <55dbe7ee-8e4a-4f09-b00e-8e879d8f6ad6@amd.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0149.namprd04.prod.outlook.com (2603:10b6:303:84::34) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) 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: SJ2PR11MB7573:EE_|DS7PR11MB8808:EE_ X-MS-Office365-Filtering-Correlation-Id: 5ad1e391-6a09-49d0-444f-08ddebd97e96 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016|13003099007; 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The >> counters of any other RMIDs which are no longer being tracked will be reset >> to zero. The MBM event counters return "Unavailable" for the RMIDs that are >> not tracked by hardware. So, there can be only limited number of groups >> that can give guaranteed monitoring numbers. With ever changing >> configurations there is no way to definitely know which of these groups are >> being tracked during a particular time. Users do not have the option to >> monitor a group or set of groups for a certain period of time without >> worrying about RMID being reset in between. >> >> The ABMC feature allows users to assign a hardware counter to an RMID, >> event pair and monitor bandwidth usage as long as it is assigned. The >> hardware continues to track the assigned counter until it is explicitly >> unassigned by the user. There is no need to worry about counters being >> reset during this period. Additionally, the user can specify the type of >> memory transactions (e.g., reads, writes) for the counter to track. >> >> Without ABMC enabled, monitoring will work in current mode without >> assignment option. >> >> The Linux resctrl subsystem provides an interface that allows monitoring of >> up to two memory bandwidth events per group, selected from a combination of >> available total and local events. When ABMC is enabled, two events will be >> assigned to each group by default, in line with the current interface >> design. Users will also have the option to configure which types of memory >> transactions are counted by these events. >> >> Due to the limited number of available counters (32), users may quickly >> exhaust the available counters. If the system runs out of assignable ABMC >> counters, the kernel will report an error. In such cases, users will need >> to unassign one or more active counters to free up counters for new >> assignments. resctrl will provide options to assign or unassign events >> through the group-specific interface file. >> >> The feature is detected via CPUID_Fn80000020_EBX_x00 bit 5. >> Bits Description >> 5 ABMC (Assignable Bandwidth Monitoring Counters) >> >> The feature details are documented in APM listed below [1]. >> [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming >> Publication # 24593 Revision 3.41 section 19.3.3.3 Assignable Bandwidth >> Monitoring (ABMC). >> >> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 >> Signed-off-by: Babu Moger >> Reviewed-by: Reinette Chatre > > This is an FYI. I am updating the text about the documentation to address > your comment. > https://lore.kernel.org/lkml/53387aa7-0e72-4bf9-a188-43c0f78c2d6f@intel.com/ > > > The ABMC feature details are documented in APM [1] available from [2]. > [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming > Publication # 24593 Revision 3.41 section 19.3.3.3 Assignable Bandwidth > Monitoring (ABMC). > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 # [2] > > > > Hope it is fine. Yes, thank you. I think this is a helpful addition. I assume this change will be applied to all patches in this series that contain this pattern? Reinette