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Wed, 15 Oct 2025 16:28:10 +0000 Message-ID: <95cb85d9-f018-4e71-88bc-f4129227bcf2@intel.com> Date: Thu, 16 Oct 2025 00:27:55 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/19] sched/fair: Record per-LLC utilization to guide cache-aware scheduling decisions To: Peter Zijlstra , Tim Chen CC: Ingo Molnar , K Prateek Nayak , "Gautham R . Shenoy" , Vincent Guittot , Juri Lelli , "Dietmar Eggemann" , Steven Rostedt , Ben Segall , Mel Gorman , "Valentin Schneider" , Madadi Vineeth Reddy , 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: <7684e7381c61a2a0d0580790340d4daa5349e48c.1760206683.git.tim.c.chen@linux.intel.com> <20251015101519.GN3289052@noisy.programming.kicks-ass.net> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <20251015101519.GN3289052@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: KL1PR01CA0071.apcprd01.prod.exchangelabs.com (2603:1096:820:5::35) 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_|SJ5PPF0DADD6EFE:EE_ X-MS-Office365-Filtering-Correlation-Id: 7c01e4c2-c672-4ac7-ee9c-08de0c07d456 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|376014|1800799024; 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This domain >> + * is either the domain that spans this group(if the >> + * group is a local group), or the sibling domain of >> + * this group. >> + */ >> + struct sched_domain *sd = env->sd->child; >> + struct sched_domain_shared *sd_share; >> + >> + if (!sched_feat(SCHED_CACHE) || env->idle == CPU_NEWLY_IDLE) >> + return; >> + >> + /* only care about sched domains spanning a LLC */ >> + if (sd != rcu_dereference(per_cpu(sd_llc, env->dst_cpu))) >> + return; >> + >> + /* >> + * At this point we know this group spans a LLC domain. >> + * Record the statistic of this group in its corresponding >> + * shared LLC domain. >> + */ >> + sd_share = rcu_dereference(per_cpu(sd_llc_shared, >> + cpumask_first(sched_group_span(group)))); > > Isn't this sd->shared ? Or did I loose the plot somewhere? > The sd here refers to the domain that covers the local_group, which is derived from env->dst_cpu. Meanwhile, sd_share corresponds to the domain covering the 'group' that may be a sibling of the local_group. Our goal is to update the statistics of this latter 'group'. It is assumed that the local_group and its sibling 'group' have the same CPU weight, meaning they each cover one LLC. We check sd simply because it is the only domain we can obtain via env->sd->child (apologies, but I haven’t found a way to get the corresponding domain that spans the 'group' itself). thanks, Chenyu