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b=EwDHsf3O1QNChytfXhypdBIvOSWGfR7MYxFI+h2uFLIop2ThbUI3r+2TCD20AhWhXIv/vh2FLkm74wyl6kNZsmuP583mJgxz8eqQoutjmx8yC5dkayHsttL0u1v8YSXDFsrlAPbKwiF5XklRmeuC7+aoykySDYDakim6Vx6yCAY= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from MW3PR12MB4553.namprd12.prod.outlook.com (2603:10b6:303:2c::19) by CH3PR12MB8258.namprd12.prod.outlook.com (2603:10b6:610:128::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8069.17; Tue, 15 Oct 2024 20:42:50 +0000 Received: from MW3PR12MB4553.namprd12.prod.outlook.com ([fe80::b0ef:2936:fec1:3a87]) by MW3PR12MB4553.namprd12.prod.outlook.com ([fe80::b0ef:2936:fec1:3a87%5]) with mapi id 15.20.8048.029; Tue, 15 Oct 2024 20:42:50 +0000 Message-ID: <42c4ac2f-2b18-48d9-89b4-5c88659bee2e@amd.com> Date: Tue, 15 Oct 2024 15:42:46 -0500 User-Agent: Mozilla Thunderbird Reply-To: babu.moger@amd.com Subject: Re: [PATCH v8 19/25] x86/resctrl: Auto assign/unassign counters when mbm_cntr_assign is enabled To: Reinette Chatre , "Luck, Tony" Cc: "corbet@lwn.net" , "Yu, Fenghua" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "paulmck@kernel.org" , "rdunlap@infradead.org" , "tj@kernel.org" , "peterz@infradead.org" , "yanjiewtw@gmail.com" , "kim.phillips@amd.com" , "lukas.bulwahn@gmail.com" , "seanjc@google.com" , "jmattson@google.com" , "leitao@debian.org" , "jpoimboe@kernel.org" , "Edgecombe, Rick P" , "kirill.shutemov@linux.intel.com" , "Joseph, Jithu" , "Huang, Kai" , "kan.liang@linux.intel.com" , "daniel.sneddon@linux.intel.com" , "pbonzini@redhat.com" , "sandipan.das@amd.com" , "ilpo.jarvinen@linux.intel.com" , "peternewman@google.com" , "Wieczor-Retman, Maciej" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Eranian, Stephane" , "james.morse@arm.com" References: <541d6c15-ed5f-8794-506c-8fa4065ca170@amd.com> <43654ae1-c894-409b-bcb8-065940644906@amd.com> <567bd687-a69f-46fb-ab19-3f8d95c5e798@intel.com> <8fa57edb-996c-4867-8a7e-05a8fcb9fe3a@intel.com> Content-Language: en-US From: "Moger, Babu" In-Reply-To: <8fa57edb-996c-4867-8a7e-05a8fcb9fe3a@intel.com> Content-Type: text/plain; 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I think Tony has a good point that since >>> assignment failures do not matter it unnecessarily complicates the code to >>> have rdtgroup_assign_cntrs() return failure. >>> >>> I also think the internals of rdtgroup_assign_cntrs() deserve a closer look. >>> I assume that error handling within rdtgroup_assign_cntrs() was created with >>> ABMC in mind. When only considering ABMC then the only reason why >>> rdtgroup_assign_cntr_event() could fail is if the system ran out of counters >>> and then indeed it makes no sense to attempt another call to rdtgroup_assign_cntr_event(). >>> >>> Now that the resctrl fs/arch split is clear the implementation does indeed expose >>> another opportunity for failure ... if the arch callback, resctrl_arch_config_cntr() >>> fails. It could thus be possible for the first rdtgroup_assign_cntr_event() to fail >>> while the second succeeds. Earlier [1], Tony suggested to, within rdtgroup_assign_cntrs(), >>> remove the local ret variable and have it return void. This sounds good to me. >>> When doing so a function comment explaining the usage will be helpful. >>> >>> I also think that rdtgroup_unassign_cntrs() deserves similar scrutiny. Even more >>> so since I do not think that the second rdtgroup_unassign_cntr_event() >>> should be prevented from running if the first rdtgroup_unassign_cntr_event() fails. >> >> >> Sounds fine with me. Now it will look like this below. > > Thank you for considering. > >> >> > > I assume that you will keep rdtgroup_assign_cntrs() function comment? I think > it may need some small changes to go with the function now returning void ... > for example, saying "Each group *requires* two counters" and then not failing when > two counters cannot be allocated seems suspect. > > For example (please feel free to improve): > > 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. > Looks good. Thanks -- Thanks Babu Moger