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Tue, 11 Aug 2026 07:46:23 +0000 Message-ID: <9fae7258-5f33-4ddc-8d21-599db3c0d091@intel.com> Date: Tue, 11 Aug 2026 15:46:12 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 1/2] sched/cache: Reduce the overhead of task_cache_work by only scan the visisted cpus To: Luo Gengkun CC: , , , , , , , , , , , , "chen.yu@linux.dev" , Jianyong Wu References: <20260731024417.1106503-1-luogengkun2@huawei.com> <20260731024417.1106503-2-luogengkun2@huawei.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SI1PR02CA0036.apcprd02.prod.outlook.com (2603:1096:4:1f6::20) 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_|DS0PR11MB7558:EE_ X-MS-Office365-Filtering-Correlation-Id: 23e2a97d-9aa6-4e6e-da45-08def77ca3dd X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|1800799024|366016|376014|7416014|11063799006|56012099006|10067099003|4143699003|22082099003|18002099003; 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>>           rq->cpu_runtime += delta_exec; >>           epoch = rq->cpu_epoch; >> +        pcpu_sched->epoch_last_visit = epoch; >> +        if (!cpumask_test_cpu(cpu_of(rq), mm->sc_stat.visited_cpus)) >> +            cpumask_set_cpu(cpu_of(rq), mm->sc_stat.visited_cpus); visited_cpus bits are only cleared inside fraction_mm_sched(), which is reachable in task_cache_work() - but that loop is skipped when invalid_llc_nr() returns true for any single-threaded process. As a result, single-threaded processes keep setting bits in account_mm_sched() without using them. Maybe a gate would be useful: if (get_nr_threads(p) > 1 && !cpumask_test_cpu(cpu_of(rq), mm->sc_stat.visited_cpus)) cpumask_set_cpu(cpu_of(rq), mm->sc_stat.visited_cpus); [ ... ] >> @@ -1866,7 +1835,18 @@ static void task_cache_work(struct >> callback_head *work) >>       scoped_guard (cpus_read_lock) { >>           guard(rcu)(); >> -        get_scan_cpumasks(cpus, p); I'm thinking of if this could bring cross-node bouncing. Is it doable to honor the result from NUMA preference: get_scan_cpumasks(cpus, p); cpumask_and(cpus, cpus, mm->sc_stat.visited_cpus); thanks, Chenyu