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Fri, 3 Apr 2026 05:46:44 +0000 Message-ID: <3b66e8e8-07e0-4f3e-a3ba-d97133af5162@intel.com> Date: Fri, 3 Apr 2026 13:46:36 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/4] sched/rt: Split cpupri_vec->cpumask to per NUMA node to reduce contention To: K Prateek Nayak , Peter Zijlstra CC: Tim Chen , Pan Deng , , , References: <20260320124003.GU3738786@noisy.programming.kicks-ass.net> <63a095f02428700a7ff2623b8ea81e524a406834.camel@linux.intel.com> <20260324120008.GB3738010@noisy.programming.kicks-ass.net> <138c3f9d-309f-41e6-aa72-a3f6bd713bf0@intel.com> <22072ef8-5aec-49ac-9cc4-8a80bec14261@amd.com> <64649c85-29ab-4f70-a0c4-3c83cbdae2fc@intel.com> <20260402105530.GA3738786@noisy.programming.kicks-ass.net> <93d7eb33-c3a5-4498-bc26-57806b73d9e0@amd.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <93d7eb33-c3a5-4498-bc26-57806b73d9e0@amd.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SI2PR02CA0018.apcprd02.prod.outlook.com (2603:1096:4:194::18) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) 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: DM4PR11MB6020:EE_|SJ1PR11MB6177:EE_ X-MS-Office365-Filtering-Correlation-Id: d62de7ee-b677-4cac-9d7e-08de91446308 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|18002099003|56012099003|22082099003; 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/* All are u64 */ >>> >>> expecting just the u64 bitmap to represent all the CPUs in the leaf. >>> >>> If we have, say 256 CPUs per DIE, we get shift(7) and arch_sbm_mask >>> as 7f (127) which allows a leaf to more than 64 CPUs but we are >>> using the "u64 bitmap" directly and not: >>> >>> find_next_bit(bitmap, arch_sbm_mask) >>> >>> Am I missing something here? >> >> Nope. That logic just isn't there, that was left as an exercise to the >> reader :-) > > Ack! Let me go fiddle with that. > Nice catch. I hadn't noticed this since we have fewer than 64 CPUs per die. Please feel free to send patches to me when they're available. And regarding your other question about the calculation of arch_sbm_shift, I'm trying to understand why there is a subtraction of 1, should it be: - arch_sbm_shift = x86_topo_system.dom_shifts[TOPO_DIE_DOMAIN] - 1; + arch_sbm_shift = x86_topo_system.dom_shifts[TOPO_DIE_DOMAIN - 1]; ? Are we trying to filer the raw global unique die id? - similar to topo_apicid() which mask the lower x86_topo_system.dom_shifts[dom - 1]). With above change I can get a correct value of leaves (4) rather than (2) in the original version. thanks, Chenyu