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Tue, 13 Oct 2026 05:30:20 +0000 Date: Tue, 13 Oct 2026 13:17:13 +0800 From: Chen Yu To: Vincent Guittot CC: , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH 07/18] sched/fair: Add push task mechanism for fair Message-ID: References: <20261002154415.2270586-1-vincent.guittot@linaro.org> <20261002154415.2270586-8-vincent.guittot@linaro.org> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: SG2P153CA0008.APCP153.PROD.OUTLOOK.COM (2603:1096::18) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6020:EE_|MW3PR11MB4748:EE_ X-MS-Office365-Filtering-Correlation-Id: 8b0afd60-13ab-4585-49b4-08df28eb12c8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|1800799024|376014|23010399003|11063799006|261009223027099003|56012099006|4143699003|10067099003|22082099003|18002099003|6133799003; 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> > > > > > > > + /* > > > > + * Only a push triggered by cache aware scheduling will push the > > > > + * task towards its preferred LLC. Pushes for other reasons, like short > > > > + * slice task, uses the default push strategy. > > > > + */ > > > > + push_cpu = -1; > > > > + if (select_flags & WF_RQ_PUSH) > > > > + push_cpu = check_pushable_cache_task(prev_cpu, p); > > > > > > Is there any reason that you do'nt want to migrate the task at wakeup too ? > > > > > > > The wakeup path seems to be too fast to aggregate the tasks, so that multiple > > CPUs try to migrate the task to the same LLC without synchronization - a task > > bouncing issue was observed when cache-aware migration was enabled in the wakeup > > path. We can double-check in the latest kernel to see if that is still the case, > > and to see if we can mitigate that. > > Yeah, the goal is to use the same select function for all events; > wakeup and push events should be seen as the same event > > Also you should separate the check for adding the task in the pushable > list in fair_check_pushable_task from the decision to select pref_cpu > in select_task_rq_fair. The check added in fair_check_pushable_task is > mainly used to decide if it worth going deeper in the decision with > select_task_rq_fair > Do you mean the check in fair_check_pushable_task() should be lightweight and let select_task_rq_fair() make the decision as to which CPU the task should be migrated to, because the former does not hold pi_lock and thus should be best-effort? OK, let me adjust the code. thanks, Chenyu > Vincent > > > > > thanks, > > Chenyu