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Wed, 15 Oct 2025 16:04:10 +0000 Message-ID: <5badc525-f745-452d-b2ae-1f58d5271aae@intel.com> Date: Thu, 16 Oct 2025 00:03:55 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 10/19] sched/fair: Prioritize tasks preferring destination LLC during balancing 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 , Libo Chen , Adam Li , Tim Chen , References: <20251015151005.GC3168635@noisy.programming.kicks-ass.net> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <20251015151005.GC3168635@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: KU0P306CA0034.MYSP306.PROD.OUTLOOK.COM (2603:1096:d10:29::10) 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_|DS4PPF990BCE628:EE_ X-MS-Office365-Filtering-Correlation-Id: ff05dc20-d17d-4473-3932-08de0c0479f3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016; 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>> + int llc; >> + >> + if (!sched_cache_enabled()) >> + return false; >> + >> + if (env->sd->flags & SD_SHARE_LLC) >> + return false; >> + >> + /* only care about task migration among LLCs */ >> + if (child && !(child->flags & SD_SHARE_LLC)) >> + return false; >> + >> + llc = llc_idx(env->dst_cpu); >> + if (sgs->nr_pref_llc[llc] > 0 && > > Robot says llc can be -1 here, and it don't like doing out of bound > array access. > Humm, there seems to be a race condition during bootup with build_sched_domains(), where the per-cpu(sd_llc_idx) is reset to -1 at the beginning. We might need to add a sanity check here. thanks, Chenyu >> + can_migrate_llc(env->src_cpu, env->dst_cpu, 0, true) == mig_llc) >> + return true; >> + >> + return false; >> +}