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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 CO1PEPF000044F5.mail.protection.outlook.com (10.167.241.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9320.13 via Frontend Transport; Mon, 10 Nov 2025 03:58:47 +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; Sun, 9 Nov 2025 19:58:46 -0800 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; Sun, 9 Nov 2025 19:58:43 -0800 Message-ID: Date: Mon, 10 Nov 2025 09:28:42 +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 v3] sched/fair: Skip sched_balance_running cmpxchg when balance is not due To: Shrikanth Hegde , Tim Chen , Peter Zijlstra CC: Ingo Molnar , Chen Yu , Doug Nelson , Mohini Narkhede , , Vincent Guittot References: <52fcd1e8582a6b014a70f0ce7795ce0d88cd63a8.1762470554.git.tim.c.chen@linux.intel.com> <1d6c22aa-c882-4833-b0be-a3999d684885@amd.com> <2edf1a85-4736-4e8b-bfc9-003dd1f34be7@linux.ibm.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <2edf1a85-4736-4e8b-bfc9-003dd1f34be7@linux.ibm.com> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Nov 2025 03:58:47.1404 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f62a24ea-dec3-4c83-a4b4-08de200d7335 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: CO1PEPF000044F5.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV3PR12MB9168 Hello Shrikanth, On 11/7/2025 2:27 PM, Shrikanth Hegde wrote: >>>   @@ -11768,6 +11784,13 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq, >>>           goto out_balanced; >>>       } >>>   +    if (idle != CPU_NEWLY_IDLE && (sd->flags & SD_SERIALIZE)) { > > Can you also try removing "idle != CPU_NEWLY_IDLE" and see the workload behavior? > If workloads don't observe regression, it might be worth serializing it too. P.S. In one of my previous testing, I had tested only serialized for !env.idle (__CPU_NOT_IDLE) and I didn't spot any difference in my benchmark runs compared to always serializing. I believe the "max_newidle_lb_cost" along with the plethora of need_resched() checks we have help bail out of newidle balance if there is a wakeup on the same CPU. Idle balance too was okay with a greater number of search. If the first CPU of group fails to pull any task and remains idle, all the other idle CPUs simply bail out at should_we_balance() which is probably why there was no difference in the set of benchmarks I tested. Serializing all shouldn't make it any worse that what we have now so I don't mind either. -- Thanks and Regards, Prateek