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Thu, 19 Dec 2024 23:59:44 +0000 Message-ID: Date: Thu, 19 Dec 2024 15:59:40 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 19/24] x86/resctrl: Report "Unassigned" for MBM events in mbm_cntr_assign mode To: Babu Moger , , , , , , , CC: , , , , , , , , , , , , , , , , , , , , , , , , , References: <2b59ada547e0444755201f269fc99240b3195e1f.1734034524.git.babu.moger@amd.com> Content-Language: en-US From: Reinette Chatre In-Reply-To: <2b59ada547e0444755201f269fc99240b3195e1f.1734034524.git.babu.moger@amd.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR03CA0032.namprd03.prod.outlook.com (2603:10b6:303:8e::7) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ2PR11MB7573:EE_|SA1PR11MB6757:EE_ X-MS-Office365-Filtering-Correlation-Id: 50f9244f-b0d4-4202-c1a0-08dd20893590 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|376014|1800799024|7416014|366016|7053199007; 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These are named "mon_sub_L3_YY" > where "YY" is the node number. > > + When supported the mbm_cntr_assign mode allows users to assign a "When supported" -> "When enabled"? Or perhaps just drop that and start with "mbm_cntr_assign mode allows users ..." > + counter to mon_hw_id, event pair enabling bandwidth monitoring for > + as long as the counter remains assigned. The hardware will continue > + tracking the assigned mon_hw_id until the user manually unassigns > + it, ensuring that counters are not reset during this period. With > + a limited number of counters, the system may run out of assignable > + counters. In that case, MBM event counters will return 'Unassigned' > + when the event is read. Users must manually assign a counter to read > + the events. > + > "mon_hw_id": > Available only with debug option. The identifier used by hardware > for the monitor group. On x86 this is the RMID. > diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c > index 200d89a64027..8e265a86e524 100644 > --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c > +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c > @@ -527,6 +527,12 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r, > /* When picking a CPU from cpu_mask, ensure it can't race with cpuhp */ > lockdep_assert_cpus_held(); > > + if (resctrl_arch_mbm_cntr_assign_enabled(r) && is_mbm_event(evtid) && > + !mbm_cntr_assigned(r, d, rdtgrp, evtid)) { > + rr->err = -ENOENT; > + return; > + } > + hmmm ... d can be NULL here after the SNC support. Since the file that needs a sum is essentially software backed I do not think assigning counters would apply to it (but it may theoretically apply to the domains it consists of). I think it may be safer to just move this check into rdtgroup_mondata_show() where it reads data for a single domain. I am not sure if we need to change the documentation because of this. One option could be a rewording to "MBM event counters may return 'Unassigned' or 'Unavailable' when the event is read". Reinette