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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by SN1PEPF00036F43.mail.protection.outlook.com (10.167.248.27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8655.12 via Frontend Transport; Fri, 18 Apr 2025 12:13:40 +0000 Received: from [172.31.188.187] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Fri, 18 Apr 2025 07:13:37 -0500 Message-ID: <331fb3d6-33f3-4656-a134-3ab3a245e477@amd.com> Date: Fri, 18 Apr 2025 17:43:34 +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] sched: Skip useless sched_balance_running acquisition if load balance is not due To: Peter Zijlstra CC: Vincent Guittot , Shrikanth Hegde , "Chen, Yu C" , Tim Chen , Ingo Molnar , Doug Nelson , Mohini Narkhede , References: <20250416035823.1846307-1-tim.c.chen@linux.intel.com> <667f2076-fbcd-4da7-8e4b-a8190a673355@intel.com> <5e191de4-f580-462d-8f93-707addafb9a2@linux.ibm.com> <517b6aac-7fbb-4c28-a0c4-086797f5c2eb@linux.ibm.com> <7a5a5f1f-0bbc-4a63-b2aa-67bc6c724b2d@amd.com> <20250417120130.GE17910@noisy.programming.kicks-ass.net> <87728994-b928-45b3-a6a0-258af6e81294@amd.com> <20250418092828.GP38216@noisy.programming.kicks-ass.net> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20250418092828.GP38216@noisy.programming.kicks-ass.net> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Apr 2025 12:13:40.8821 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 274d03db-bc76-46d2-9775-08dd7e7274eb 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=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SN1PEPF00036F43.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR12MB8030 Hello Peter, On 4/18/2025 2:58 PM, Peter Zijlstra wrote: > On Fri, Apr 18, 2025 at 10:56:04AM +0530, K Prateek Nayak wrote: >> Hello Peter, >> >> On 4/17/2025 5:31 PM, Peter Zijlstra wrote: >>>> o Since this is a single flag across the entire system, it also implies >>>> CPUs cannon concurrently do load balancing across different NUMA >>>> domains which seems reasonable since a load balance at lower NUMA >>>> domain can potentially change the "nr_numa_running" and >>>> "nr_preferred_running" stats for the higher domain but if this is the >>>> case, a newidle balance at lower NUMA domain can interfere with a >>>> concurrent busy / newidle load balancing at higher NUMA domain. >>>> Is this expected? Should newidle balance be serialized too? >>> >>> Serializing new-idle might create too much idle time. >> >> In the context of busy and idle balancing, What are your thoughts on a >> per sd "serialize' flag? > > My sekret hope is that this push stuff can rid us all the idle balance > bits. But yeah, early days on that. > > Other than that, I don't quite see why we should split that, busy > balancing is the one that runs more often and is the one that should be > serialized to avoid too much cross node traffic and all that, no? > > The idle thing is less often, why not limit that? Makes sense. I'll add it to the set of my weekend experiment runs. -- Thanks and Regards, Prateek