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Wed, 16 Jul 2025 15:58:42 +0000 Message-ID: Date: Wed, 16 Jul 2025 23:58:33 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] sched/fair: bump sd->max_newidle_lb_cost when newidle balance fails To: Peter Zijlstra CC: kernel test robot , Chris Mason , , , , , References: <202507150846.538fc133-lkp@intel.com> <10abe013-98d6-4080-ac43-0f1e02aa41f9@intel.com> <20250716112533.GS1613200@noisy.programming.kicks-ass.net> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <20250716112533.GS1613200@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SG2PR02CA0018.apcprd02.prod.outlook.com (2603:1096:3:17::30) 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_|PH0PR11MB5926:EE_ X-MS-Office365-Filtering-Correlation-Id: e731ba2d-c6d4-46f7-e095-08ddc481a2b0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024; 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So when newidle balance is not succeeding to pull > tasks, it is backing off and doing less of it. > >> It seems that some workloads >> do not like newlyidle balance, like schbench, which is short duration >> task. While other workloads want the newidle balance to pull at its best >> effort, like unixbench shell test case. >> Just wonder if we can check the sched domain's average utilization to >> decide how hard we should trigger the newly idle balance, or can we check >> the overutilized flag to decide whether we should launch the >> new idle balance, something I was thinking of: > > Looking at the actual util signal might be interesting, but as Chris > already noted, overutilized isn't the right thing to look at. Simply > taking rq->cfs.avg.util_avg might be more useful. Very high util and > failure to pull might indicate new-idle just isn't very important / > effective. While low util and failure might mean we should try harder. > > Other things to look at: > > - if the sysctl_sched_migration_cost limit isn't artificially limiting > actual scanning costs. Eg. very large domains might perhaps have > costs that are genuinely larger than that somewhat random number. > > - if despite the apparent failure to pull, we do already have something > to run (eg. wakeups). > > - if the 3/2 backoff is perhaps too aggressive vs the 1% per second > decay. Thanks for the suggestions, let me try to reproduce this issue locally to see what is the proper way to get it addressed. thanks, Chenyu