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Tue, 9 Jun 2026 06:24:25 +0000 Message-ID: <32d47573-75fd-4a8f-aefb-ce7fb1136346@intel.com> Date: Tue, 9 Jun 2026 14:24:14 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/6] sched/fair: Do not skip CPUs of similar capacity with busy SMT siblings To: K Prateek Nayak , Ricardo Neri CC: "Rafael J. Wysocki" , Ingo Molnar , Peter Zijlstra , Andrea Righi , "Len Brown" , , , Juri Lelli , "Steven Rostedt" , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Tim C Chen , Valentin Schneider , Christian Loehle , Barry Song References: <20260608-rneri-fix-cas-clusters-v4-0-1526711c944c@linux.intel.com> <20260608-rneri-fix-cas-clusters-v4-1-1526711c944c@linux.intel.com> <1ee48251-8f70-4632-bb4b-79760c1c8a8b@amd.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <1ee48251-8f70-4632-bb4b-79760c1c8a8b@amd.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: TP0P295CA0032.TWNP295.PROD.OUTLOOK.COM (2603:1096:910:4::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_|IA0PR11MB8399:EE_ X-MS-Office365-Filtering-Correlation-Id: 7e74f86e-eb08-4f29-1a3f-08dec5efc087 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|376014|22082099003|18002099003|4143699003|11063799006|56012099006; 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>> >> for_each_cpu_and(i, sched_group_span(group), env->cpus) { >> + bool smt_degraded_cap = sched_smt_active() && !is_core_idle(i); > > Based on a quick look at the generated asm, we seem to be calculating > "smt_degraded_cap" regardless of whether we are on a > "SD_ASYM_CPUCAPACITY" domain or not which is an unnecessary overhead of > doing a is_core_idle() on symmetric domains. > > We can have an indicator up top like: > > bool asym_balance = !!(env->sd->flags & SD_ASYM_CPUCAPACITY); > > and later use that when computing smt_degraded_cap: > > bool smt_degraded_cap = asym_balance && (sched_smt_active() && !is_core_idle(i)); > > I would even suggest pushing this until later and do ... > Right, this can leverage if (!nr_running) to skip the idle i, thus avoid doing is_core_idle(). >> unsigned long capacity, load, util; >> unsigned int nr_running; >> enum fbq_type rt; >> @@ -12964,8 +12965,12 @@ static struct rq *sched_balance_find_src_rq(struct lb_env *env, >> * eventually lead to active_balancing high->low capacity. >> * Higher per-CPU capacity is considered better than balancing >> * average load. >> + * >> + * Busy SMT siblings reduce the capacity of CPU i. Do not skip >> + * it in this case. >> */ >> if (env->sd->flags & SD_ASYM_CPUCAPACITY && > > ... > > if (asym_balance) { > /* Busy SMT reduces capacity */ > if (sched_smt_active() && !is_core_idle(i)) > continue; We might not want to skip i if it has SMT busy siblings? if ((!sched_smt_active() || is_core_idle(i)) && ... thanks, Chenyu