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client-ip=165.204.84.17; helo=satlexmb08.amd.com; pr=C Received: from satlexmb08.amd.com (165.204.84.17) by BL02EPF0002992B.mail.protection.outlook.com (10.167.249.56) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9891.9 via Frontend Transport; Wed, 6 May 2026 10:20:01 +0000 Received: from satlexmb07.amd.com (10.181.42.216) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.17; Wed, 6 May 2026 05:20:00 -0500 Received: from [172.31.184.125] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Wed, 6 May 2026 05:19:55 -0500 Message-ID: Date: Wed, 6 May 2026 15:49:54 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/5] sched/fair: Attach sched_domain_shared to sd_asym_cpucapacity To: Vincent Guittot , Andrea Righi CC: Ingo Molnar , Peter Zijlstra , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Christian Loehle , Koba Ko , Felix Abecassis , Balbir Singh , Joel Fernandes , Shrikanth Hegde , References: <20260428144352.3575863-1-arighi@nvidia.com> <20260428144352.3575863-3-arighi@nvidia.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: sUtwg4r952dkkjohyI49Q1OzblNr+jd4hF0qVvPEGwHB16XM9sG3kTNDS2+WXIQ4jzTTyLMHJ7uPJbD4XkfuOFnc/hpGEMQDVEZiXZmEsu+UYONDihrT7xbVLB2x9EmEIgWxjShn3CVBuVVe3t1xSMLtctAbFMqacteEWhqGzK5Vy501y148amxFgpBYJZ1L3yr3/Xt/uiZd4fx9zSoIzMz57Uc9Q8w2Tl4Ry+ibr6cJFxU9EPlt411BPnNhz0PvapIr+yNA4S9RyBRb8YuF7nYS+IyI2WXZ9a6G/5ZemADj46jFeVTWUP5+LZLkYONgpCRVZTZOqJ+lkl9Rhq30YMEI+bKKZtX6Cq57Tn3J487Cyrvm2+br8KCMHxIi7jToiJHRyLAsSLZev1F/C2mkeqDCTjmGCI148jt/a4012MIrBik3SAJDuHeLbrF3EZfe X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2026 10:20:01.1894 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d0372443-5876-4341-477b-08deab590844 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BL02EPF0002992B.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB7568 Hello Vincent, On 5/6/2026 3:15 PM, Vincent Guittot wrote: >> @@ -7925,7 +7925,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool >> struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask); >> int i, cpu, idle_cpu = -1, nr = INT_MAX; >> >> - if (sched_feat(SIS_UTIL)) { >> + if (sched_feat(SIS_UTIL) && sd->shared) { > > If shared is attached to sd_asym_cpucapacity instead of sd_llc we > should never reach this point. Or I'm missing a case ? So the hotpulg might race with a wakeup like: claim_asym_sched_domain_shared() init_sched_domain_shared(d, sd_asym); return true; update_top_cache_domain() rcu_assign_pointer(sd_llc, sd); ... select_idle_sibling() sd = rcu_dereference_all(sd_asym_cpucapacity) /* sd_asym_cpucapacity still hasn't been updated */ if (sd /* NULL */) { ... } sd = rcu_dereference_all(sd_llc); /* Valid */ select_idle_cpu(sd) rcu_assign_pointer(sd_asym_cpucapacity, sd); sd->shared /* NULL */ This prevents that rare race where a remote CPU will see sd_llc before sd_asym is published and take the !ASYM wakeup route only to find sd->shared is NULL since sd_asym has claimed it. > >> /* >> * Increment because !--nr is the condition to stop scan. >> * -- Thanks and Regards, Prateek