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Thu, 16 Oct 2025 03:11:28 +0000 Message-ID: Date: Thu, 16 Oct 2025 11:11:12 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 01/19] sched/fair: Add infrastructure for cache-aware load balancing To: Tim Chen , Madadi Vineeth Reddy CC: Peter Zijlstra , Ingo Molnar , "K Prateek Nayak" , "Gautham R . Shenoy" , Vincent Guittot , "Juri Lelli" , Dietmar Eggemann , Steven Rostedt , Ben Segall , "Mel Gorman" , Valentin Schneider , "Hillf Danton" , Shrikanth Hegde , "Jianyong Wu" , Yangyu Chen , Tingyin Duan , Vern Hao , Len Brown , Aubrey Li , Zhao Liu , Chen Yu , Adam Li , Tim Chen , , References: <865b852e3fdef6561c9e0a5be9a94aec8a68cdea.1760206683.git.tim.c.chen@linux.intel.com> <22750d4a-fdd6-48ad-a2ca-aa0c12af329c@linux.ibm.com> <5f140e59-23f9-46dd-bf5e-7bef0d897cd0@intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: KUZPR01CA0006.apcprd01.prod.exchangelabs.com (2603:1096:d10:34::19) 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_|PH7PR11MB5958:EE_ X-MS-Office365-Filtering-Correlation-Id: 317bcfc9-4d32-4bed-af03-08de0c61b2d7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|376014; 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Also scanning multiple >>> nodes add overhead, so can restricting it to numa preferred node be >>> better and scan others only when there is no numa preferred node? >>> >> >> Basically, yes, you're right. Ideally, we should prioritize the NUMA >> preferred node as the top priority. There's one case I find hard to >> handle: the NUMA preferred node is per task rather than per process. >> It's possible that different threads of the same process have different >> preferred nodes; as a result, the process-wide preferred LLC could bounce >> between different nodes, which might cause costly task migrations across >> nodes. As a workaround, we tried to keep the scan CPU mask covering the >> process's current preferred LLC to ensure the old preferred LLC is included >> in the candidates. After all, we have a 2X threshold for switching the >> preferred LLC. > > If tasks in a process had different preferred nodes, they would > belong to different numa_groups, and majority of their data would > be from different NUMA nodes. > > To resolve such conflict, we'll need to change the aggregation of tasks by > process, to aggregation of tasks by numa_group when NUMA balancing is > enabled. This probably makes more sense as tasks in a numa_group > have more shared data and would benefit from co-locating in the > same cache. > Yes, this could be an enhancement if the NUMA balance is enabled. thanks, Chenyu