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Wed, 4 Dec 2024 17:03:14 +0000 Message-ID: <4032a5a5-dd0a-49ae-94b6-dc4fac4c190d@intel.com> Date: Wed, 4 Dec 2024 09:03:10 -0800 User-Agent: Mozilla Thunderbird From: Reinette Chatre Subject: Re: [PATCH v9 20/26] x86/resctrl: Auto assign/unassign counters when mbm_cntr_assign is enabled To: Fenghua Yu , Babu Moger , , , , , CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , References: <4ec00fe60cd42c1f22c98c9f5c2f5d3ceb9f8d58.1730244116.git.babu.moger@amd.com> <3061ec99-c418-b1a3-7975-8a6b9d0bdd14@intel.com> Content-Language: en-US In-Reply-To: <3061ec99-c418-b1a3-7975-8a6b9d0bdd14@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MW4PR03CA0140.namprd03.prod.outlook.com (2603:10b6:303:8c::25) 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_|PH7PR11MB8035:EE_ X-MS-Office365-Filtering-Correlation-Id: f73ec407-4439-4e71-d4d4-08dd14858a89 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|1800799024|376014|366016|7053199007; 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Two counters >> are required per group, one for MBM total event and one for MBM local >> event. >> >> There are a limited number of counters available for assignment. If these >> counters are exhausted, the kernel will display the error message: "Out of >> MBM assignable counters". However, it is not necessary to fail the >> creation of a group due to assignment failures. Users have the flexibility >> to modify the assignments at a later time. >> >> Signed-off-by: Babu Moger >> --- >> v9: Changed rdtgroup_assign_cntrs() and rdtgroup_unassign_cntrs() to return void. >>      Updated couple of rdtgroup_unassign_cntrs() calls properly. >>      Updated function comments. >> >> v8: Renamed rdtgroup_assign_grp to rdtgroup_assign_cntrs. >>      Renamed rdtgroup_unassign_grp to rdtgroup_unassign_cntrs. >>      Fixed the problem with unassigning the child MON groups of CTRL_MON group. >> >> v7: Reworded the commit message. >>      Removed the reference of ABMC with mbm_cntr_assign. >>      Renamed the function rdtgroup_assign_cntrs to rdtgroup_assign_grp. >> >> v6: Removed the redundant comments on all the calls of >>      rdtgroup_assign_cntrs. Updated the commit message. >>      Dropped printing error message on every call of rdtgroup_assign_cntrs. >> >> v5: Removed the code to enable/disable ABMC during the mount. >>      That will be another patch. >>      Added arch callers to get the arch specific data. >>      Renamed fuctions to match the other abmc function. >>      Added code comments for assignment failures. >> >> v4: Few name changes based on the upstream discussion. >>      Commit message update. >> >> v3: This is a new patch. Patch addresses the upstream comment to enable >>      ABMC feature by default if the feature is available. >> --- >>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 61 +++++++++++++++++++++++++- >>   1 file changed, 60 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> index b0cce3dfd062..a8d21b0b2054 100644 >> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> @@ -2932,6 +2932,46 @@ static void schemata_list_destroy(void) >>       } >>   } >>   +/* >> + * Called when a new group is created. If "mbm_cntr_assign" mode is enabled, >> + * counters are automatically assigned. Each group can accommodate two counters: >> + * one for the total event and one for the local event. Assignments may fail >> + * due to the limited number of counters. However, it is not necessary to fail >> + * the group creation and thus no failure is returned. Users have the option >> + * to modify the counter assignments after the group has been created. >> + */ >> +static void rdtgroup_assign_cntrs(struct rdtgroup *rdtgrp) >> +{ >> +    struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl; >> + >> +    if (!resctrl_arch_mbm_cntr_assign_enabled(r)) >> +        return; >> + >> +    if (is_mbm_total_enabled()) >> +        rdtgroup_assign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_TOTAL_EVENT_ID); > > In this code path, > resctrl_mkdir()->resctrl_mkdir_ctrl_mon()->rdtgroup_assign_cntrs()->rdtgroup_assign_cntr_event() > > CPUs are not protected by read lock while rdtgroup_assign_cntr_event() walks r->mon_domains and run assing counters code on CPUs in the domains. Without CPU protection, r->mon_domains may race with CPU hotplug. >From what I can tell rdtgroup_assign_cntrs() is called with CPU hotplug lock held: rdtgroup_mkdir_ctrl_mon() { ret = mkdir_rdt_prepare(...); /* mkdir_rdt_prepare()->rdtgroup_kn_lock_live()->cpus_read_lock() */ ... rdtgroup_assign_cntrs(rdtgrp); ... rdtgroup_kn_unlock(parent_kn); /* rdtgroup_kn_unlock()->cpus_read_unlock() */ return ret; } Reinette