From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.14]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7082573451 for ; Mon, 13 Oct 2025 16:43:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=192.198.163.14 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760373824; cv=fail; b=bQsuyvTLeeViqfBwG/ghWvXieRjg25QRHXDPNk4QwHtUiwN5843xmNiFEiGH9Ygq4QvW15XwlxFiVWvYAEKmnGElp5q+jDHmoNbta5AxLBW6Qe9yv5d9WdWCpVMbgPN0Xk/fpQvbNztd2KbIzw/mmQQcqGTRJz+HrFoevavyytI= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760373824; c=relaxed/simple; bh=Gd3lhljm5xSBOOdHCezjRUe/gTjH07dAq7RnmSGnY/k=; h=Message-ID:Date:Subject:To:CC:References:From:In-Reply-To: Content-Type:MIME-Version; b=KriIvMq7ycMpj5YFfBSEdRxnxSvYhcKHnUPKNFhjf1BnjrInKMAPzgZzuve7RhKOyoC4CyvkpZg7yThmnEFOh2ASEBiYt85ByJCsv556E6r3GShmmtuuzPSfvM7JpFTtbaQ02sXjcQ5loATb7B5iN9BeaJi+Bbq2Z5IaN42r0kI= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=PSxWmp5W; arc=fail smtp.client-ip=192.198.163.14 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="PSxWmp5W" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1760373822; x=1791909822; h=message-id:date:subject:to:cc:references:from: in-reply-to:content-transfer-encoding:mime-version; bh=Gd3lhljm5xSBOOdHCezjRUe/gTjH07dAq7RnmSGnY/k=; b=PSxWmp5WiCX6KwOvFdbnf4nO2IT36c4TOg0sXGE3YfJF3wP7Cclbb0Go JwiPP3eT8dLAQsfHeLmHtp2QbmcBVPh7/sk+Ta/3jIpLuqtTn8Y5azudF m4ZryY+DsrMy1X+AzNBhS9ojVbyyfctKeRY6lQ52qW1MtvoYdk0IhXXa3 45N8pybKg8qJgSN6PhU5q68azWZzu3EVCmPUk3HtHjInXSV9ospAw8bVG jXsA1MIfnbVHrBqS57BJHj6wWwkb9TYeT1qkA+Xb3TZJ/sapaIdC30KbY rNQr1yrShF0bfeqWy6w+tqJvvPs+btXtr4mzVjPoYmBsy5ZnQNFNfIrKn A==; X-CSE-ConnectionGUID: lp+bBr8zQUGYS+L+Gl1VEQ== X-CSE-MsgGUID: g/r+jA+1TwqrHWFxMctuGQ== X-IronPort-AV: E=McAfee;i="6800,10657,11581"; a="62556416" X-IronPort-AV: E=Sophos;i="6.19,225,1754982000"; d="scan'208";a="62556416" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by fmvoesa108.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Oct 2025 09:43:42 -0700 X-CSE-ConnectionGUID: ZUcvzSgoTwypxVLN3wdWjw== X-CSE-MsgGUID: IK015UbHTCeCStCzvWXdTg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,226,1754982000"; d="scan'208";a="218763912" Received: from fmsmsx901.amr.corp.intel.com ([10.18.126.90]) by orviesa001.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Oct 2025 09:43:41 -0700 Received: from FMSMSX901.amr.corp.intel.com (10.18.126.90) by fmsmsx901.amr.corp.intel.com (10.18.126.90) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.27; Mon, 13 Oct 2025 09:43:40 -0700 Received: from fmsedg901.ED.cps.intel.com (10.1.192.143) by FMSMSX901.amr.corp.intel.com (10.18.126.90) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.27 via Frontend Transport; Mon, 13 Oct 2025 09:43:40 -0700 Received: from SN4PR2101CU001.outbound.protection.outlook.com (40.93.195.54) by edgegateway.intel.com (192.55.55.81) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.27; Mon, 13 Oct 2025 09:43:40 -0700 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=BK8nNlCY6N9x5qZokBI54tWTpsM9Lkm71/+T+Swuj+yvyAjxLCc6ak+OVzhoeJMzeNXm7s+anGEKYAsco9cOcBsM2jYXmjsBNx4VEDWNF6skd/3EFcvS+oP56oHyDOntccasXWXrvzFdvpiUE3XmACenmbr5/XK7dMSyrt8etjTzf/Onzr6VM7TcmeINZD9bTn0EzSKYwIBvTY3+nxh0VtLk8kCOA7wuZnacUUBkV+nZTyRYkjePJK1OwUV7tMTy/4EFGMNClb/IbRoR9LO/TX0mGvdNX8HBEi+RfR0ZFN8RfupZwL69rxO0qgXxCxztU+HU4VxNJzJ8Iuf3hvrZHg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=icgtVGLtUVhuYgAU6lamOX3Dl3V0ZY/9ORp7by7VVNs=; b=T9yo9sRQy3oH4TBRDZ/2ljs89QNvb/xpl25XasxF9yOsfx6wovQEE2FKSDyfvVUHhmLCMB2Z/bVkKjMdjFkueoiRLjJnmc8wU4JrSjO0xBycjsVNXkqaSXl3Qean7NQE2+Ew0dPSwR/N8c0I7BEOomW7J4tx+qOZV01SJPwGLnM895gGOyWuWjmxW3yFhke51zh09Do5FmvJTuU1dlciwIJIYTdRko4RpIJRQ3gD2JKNvHQ9xNHeFQDUb8BwbwGDdsNNiNzEX8EJT25ZdaMgZnw+/KGuaqLjgBgrxaaEpJND7Wv8rmT9Z6AaM3egJwSv/QBXy1bzd+A+U11ub2ZZKA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=intel.com; dmarc=pass action=none header.from=intel.com; dkim=pass header.d=intel.com; arc=none Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=intel.com; Received: from DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) by CH3PR11MB8562.namprd11.prod.outlook.com (2603:10b6:610:1b8::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9203.12; Mon, 13 Oct 2025 16:43:36 +0000 Received: from DM4PR11MB6020.namprd11.prod.outlook.com ([fe80::4af6:d44e:b6b0:fdce]) by DM4PR11MB6020.namprd11.prod.outlook.com ([fe80::4af6:d44e:b6b0:fdce%5]) with mapi id 15.20.9203.009; Mon, 13 Oct 2025 16:43:36 +0000 Message-ID: <0c9ceccb-8f77-4777-a352-090d29421394@intel.com> Date: Tue, 14 Oct 2025 00:43:27 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [RESEND PATCH] sched/fair: Skip sched_balance_running cmpxchg when balance is not due To: Shrikanth Hegde , Peter Zijlstra , Tim Chen CC: Ingo Molnar , Doug Nelson , Mohini Narkhede , , Vincent Guittot , K Prateek Nayak References: <20251013142638.GM3245006@noisy.programming.kicks-ass.net> <49dba7ff-8be6-40cf-9aa7-b0a5cb2f77c3@intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: KL1PR01CA0141.apcprd01.prod.exchangelabs.com (2603:1096:820:4::33) 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_|CH3PR11MB8562:EE_ X-MS-Office365-Filtering-Correlation-Id: 4d78e256-40ce-4254-3456-08de0a77a7c2 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024; X-Microsoft-Antispam-Message-Info: =?utf-8?B?R3hxY1dPZzF6NVVZZWxBRGRwSzFMUkJ0Vm0vRkM3SEdCdjZsRXhxSWo3TUxp?= =?utf-8?B?SkJiZjgvOFQ4T2xIWkNiV1VjdkRMZDF3YmtYOFRHUjAvSWtyVVJhamJwWjB1?= =?utf-8?B?andsK1lIOGNDYS9ONERQRXhXd2hTZlF4MDdwTXJMaFBTT2J3QjZxUHlpaWd3?= =?utf-8?B?NFpNQmx0SEdrNThIM3A0WkMvZTVHM2MvdTdDOUhlaGozZGhWM0twcFNNTXFB?= =?utf-8?B?ZkRNSFAxTFFVSkpqN3pPRXR3aXU4ZndLM3ZJV0VTWGZMaHUwdXdSOHRwMC9o?= =?utf-8?B?ZHk5VFNWNXBBdjlWbWdKTzcrNE5aUTJHencvalZSZWdJd3JENDl5YzhnUEEw?= =?utf-8?B?RzdvUWtlSGJ0VUJ2Vi9wYmVBenZ6cWgwZXZxWkVld3lUV3Ixd0loOThwTmNF?= =?utf-8?B?YjJUN2lXSUJNckp6MmhoNkhTTHJXdTZLZ3g4Y0VKNURxQ25RbHdiSkJQNnRG?= =?utf-8?B?ZkNuM1hUTnU1OEErZThER085ZUJBV1VmWUgwNDcwRGJHczlzT2FKZjZXak1v?= =?utf-8?B?Q3YzMGxocDgvYTlUSXFQUlFGbXNIbFprSVFJdnUvbjdEOE81TjNsU0R2MkVC?= =?utf-8?B?cThvVFBhaXBvWGdVTkM2bk44ak0rSWFvUjhYVWhWM3hRZWhaZFUzOWlSVmpU?= =?utf-8?B?QkVOZXM0eG1EUVFncFEwalhXSjkvZWgyQmkzOWJscEhHTFlNeDFTZm9veStO?= =?utf-8?B?L292d2p0OXk5eEQ3N21pM1dKTWZjK3dVNUtHbTBjMFFWNENBd2xaV09JWm1o?= =?utf-8?B?WTRBMmRVVjBRWkpIUm96RVVpZUhaQzU0Yzh4dk1veEY4Y2ZuVEtDbTFYM0o4?= =?utf-8?B?VFlpdkNHQ3haTFJpZ3gybXNnKy8wUjBJUTN1NlVLUnVUSHJYUmxNKzF2cnBB?= =?utf-8?B?VFVOSjBrNHlzL3NPVGFrKzBML0F2TnNMV3JsNmJUYTFHdk9Kc1FYUDAwM0Rq?= =?utf-8?B?K0twVDFidjVLQnV0MnBnZDFZLzV2b0lPenR2U3FJeGtBMldod2VxWEFpeDQ4?= =?utf-8?B?VDF3MnU1ekdobUo4eW5zbTZHT1pGWis5VHpGeVFUMjV1YW9DMkZlU1JmTXph?= =?utf-8?B?U1pDZnlVOVNGaWp4SDMxKzA0ZytVdUxRd0hkd25Qcm50RS9vaGpOT2tkOEN5?= =?utf-8?B?OWlESURZRk0rWXA3WVJzb2hUTzV3aTRSeG5FanU2Tk8zNWhkby9NOSs2QVR2?= =?utf-8?B?eGV0UWgyNFVDT2s1ck43OGtOemhxN3JnbTl6VjFWT081SEh3d3lNQnlBNlln?= =?utf-8?B?WWdGYVBPanBveDNSL1RycmVWdG82UGVkeW5jd2VTWGxZZHlFZmVWME42bkRE?= =?utf-8?B?THBHVkt1K00wN0pHSUJjT09JR25lbkxqRWhyNmpkN2Zsbk1adG10ckVTRG0w?= =?utf-8?B?S3VCVU9kYm5NcThXL0pTdnY4VkwwcEtMZjVRRFRBR2NYZjhnQ3JRMnpNQWZ4?= =?utf-8?B?K0hJZlZBbzFFeGNSdmZmSElVKzNPbTRpMm1DMGxmYTQzekkrT0VRZlBiZjNK?= =?utf-8?B?VnNPRzUwQTVFRDZKTTN2d204bFI4aHlRbG81TWFDNUhDTkVPUW9HUDMrVmRk?= =?utf-8?B?NW8vcGVIUDRabDQ4QnZnZWs3ZTRUc2ZNNWs1cjVBTkl2TFFKTnBwZndORnJY?= =?utf-8?B?cmY5Rk16MHlKV2wrZE9KQ3VnaVdIekkrVWQ4ZFBHbDNhOWM3RS9OcS9hVjFN?= =?utf-8?B?cEpERmhOQnA1SU5zdGZIM0xYOENyM1dvdVF4cER4UFNOd3dYYmZVR1I2N1pi?= =?utf-8?B?amkrbEgwd1pPN2RzME55RUNkRFpOUkk0QlNJQ0swSDh6M1VwVjkxUHJsODhK?= =?utf-8?B?SlF3VENORitoRHAwSTdSY3JKRTl4dCtpRVl5T0FVYm1yY0YzVHJ4MmZiaURp?= =?utf-8?B?bloyODNQcEdlODhOa2NIVnVsME0wL0Y5V3hQQjN3dEM5UE1XUjFLcXdiUngy?= =?utf-8?Q?zWnrFUMAT1Wz8Gd3wX9AMeVDMZDIk3c6?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM4PR11MB6020.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(376014)(1800799024);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?K2psOHE2QVhPcmEzZWRqRHVRait2eFUwNUMzdUVVZTYyTFBaVi9hOXh2bmk1?= =?utf-8?B?NDRTM1V6OTVIKzJ2Z2VvdFVCbHZkRGpVcGY4aTFjNGtPV1llVllYbmdsVGVG?= =?utf-8?B?b2pVSW1yRXRRY0NRWlE4SnlCb1RnV0Erc3E4NEJJU2ZsejUvUVlaWVVweEVh?= =?utf-8?B?SGNhN2orZUhhRVIvVlpQZTZ1K0x2eGhha0lTanB1NHF3a3RMY0E4MktVazlw?= =?utf-8?B?a1QwV3VwWU95amFqSGkyNHJEM3E5MGNKNUs0b3hmU1NKZU1IU2dud1V1NHVX?= =?utf-8?B?dHhLdGIrUXU3T0h5aHYwYWNoMUZkMFZ4MkN1Wnh3MWpXMk5rWmZza2trcHBL?= =?utf-8?B?RWs0VWloUUhBS0FKLzJBNTlOT3Fla0VMSFVoeHVuTjJ1dnBwUUlZclgxRXdR?= =?utf-8?B?aWsxZDZYM3h1c3JYRWJWUUkvRmlHZlVGTWI0WUhRVFBPdUdnVlBzUzk3MHBQ?= =?utf-8?B?YzU2SUVHSmlteFE5dTQySkpJRDNFN1drWWFtcVBSbEtGREFSR290aS9XREFj?= =?utf-8?B?V1JENmFKV3dEVEtjMDZhdkd5UHlvR2tCNnd4c2tRRW5lK2ZUQXNTVEVHbUZQ?= =?utf-8?B?UWh1UVZ2WEI2Y2xIdVpIZE8yeVhlRGNadEdlaTVYQ24yVzlNWW9nN2x6UEl1?= =?utf-8?B?M0VHNGJSekhySm13OWVrcnhYRm4rRUtQYitmWkIvRUJFT3ZOQ1dmejBNNUZT?= =?utf-8?B?ZXpiM0x6bmlaZlBNWU03bjlOYlViZ29wNXJaMTJHb3o5bVFEWGtWVzByZkFS?= =?utf-8?B?eFJJcUtzRzFVSFZMUElxUU5WQ1NubVFJK3oxTW53ZERPT2I4WU9VZkZ4b0pP?= =?utf-8?B?L3liRXhSV29ybjkvM252UGNrYXppTkJBRVBzV2NoYXVjU25nS2l6SmlKSVor?= =?utf-8?B?bFNEOElNTERtOFRheTZKY1NDd1BNZmV1UHNOSTFPSENzdjNHejJoc3R1SmFG?= =?utf-8?B?bXU0cU5QUFlLY3pib3BuaGdENXVTdGpVTFFPY21BZHBvV2N3QjhEZFhSdldz?= =?utf-8?B?V3FNZDVEbmNseDBpRjU3Q3k5Vk5uQUpwd1dlaFdIVVY3MWdsb1RJckdCTXYy?= =?utf-8?B?SFc1aGxSSlRCa1kwVmV4ZStmSXY1QzRDNjAxclViUjYvWE4yTDFXS2d5Y000?= =?utf-8?B?cU4yK2hXZDh6dnBKNm1IMFpteEhrbkc1a2ltMGRPajBzNzhta25XelhLcDN0?= =?utf-8?B?UGc2NlBEaTh3YUlhV2NqSyt0bUVxZjdzMnF6VUQyU252SjRPSC8yMDh1aEg4?= =?utf-8?B?d3cyRXpGZVJMQjFpMkN3ODV2TmhWbEwyYmZ4NGF2SnZrWHFTVHRoZDR6azZU?= =?utf-8?B?MkZDcnJUeDNmUkhkdnBKUFJ0MXhNZ1gxUzBJNzVXSEhUYjRtMlcwcm54M2Fx?= =?utf-8?B?b2FuK0dQZTljTk9zQUY2WlhIU3FLZFNHVUJva1I4cVp2Z2QwV0EyZG1iTWZq?= =?utf-8?B?a3piMklzWVlkV1JtZVg3WStrTmN4MG44R25IRUozdWNSVEpVRzZjQThRc0Ur?= =?utf-8?B?MFJWeTI4K0xwMFZGb3ZCZ2J5azQ1NXVadUVTYjlOZURzT1drMDUxa1ZSeTMy?= =?utf-8?B?T2VSbkl2WndsUm4veHZOR1Bkc01ndklNR3RGU0pzQXM3YWJWSEJuTFdicWJ2?= =?utf-8?B?eU00WUFwR2NBdEc4c3lZVVZ2allRaTlzV3RIbVVUYk5QLzRBMnVrUGFPRXhj?= =?utf-8?B?OXhnSHVuaVNjTmhaY1JuVHBkZngzcUQzNnM3M3l2eEh0WHd1RXdjaVd3M3pB?= =?utf-8?B?T2tLYTdVd1hCdXk2c0FPUXZHMStoR0ZQZmJRbXJrdi81MU80Ym5hUDRnY2VZ?= =?utf-8?B?Qlg1dXo0K0lPQXVxYk14by9nWDgrbDlCMVpNWGVpLzY2YjRkU0ZmWG93RmFR?= =?utf-8?B?QjNCSHYvQ3lVekxjdHpjeTZ0bjlFK2lkZjN6K290YWlFZEZnVmFiVlhQR2pu?= =?utf-8?B?UTdld1MwalJPTEJXWkZIUTI3Sm9yVTNYUFU0aFpERFJQblVzU0pDeFkyYTBO?= =?utf-8?B?ZjFjL2xDbWh1OVVyV3lEMHJWbzNCelgwa240cGhVNXhFTUJvK0k1cFR5WFNL?= =?utf-8?B?azY2UWxPOWNRc08zcHNDU1pqRnpNUkZXQmUyR0VERlppUTJvOVI1d3liYytx?= =?utf-8?Q?x7vGrRMlS8Y05Nh/e1Sh3DZTt?= X-MS-Exchange-CrossTenant-Network-Message-Id: 4d78e256-40ce-4254-3456-08de0a77a7c2 X-MS-Exchange-CrossTenant-AuthSource: DM4PR11MB6020.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Oct 2025 16:43:36.8122 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: iZmYW5fKEE6hRRa0FDSDjeAu5HKmY5zo1e5ORqZot8cuf2VbPqdl4Pz1lww4Rzkp06ZlPiEw5AvxfuNb2xKF1A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR11MB8562 X-OriginatorOrg: intel.com On 10/14/2025 12:41 AM, Shrikanth Hegde wrote: > > > On 10/13/25 10:02 PM, Chen, Yu C wrote: >> On 10/13/2025 10:26 PM, Peter Zijlstra wrote: >>> On Thu, Oct 02, 2025 at 04:00:12PM -0700, Tim Chen wrote: >>> >>>> During load balancing, balancing at the LLC level and above must be >>>> serialized. >>> >>> I would argue the wording here, there is no *must*, they *are*. Per the >>> current rules SD_NUMA and up get SD_SERIALIZE. >>> >>> This is a *very* old thing, done by Christoph Lameter back when he was >>> at SGI. I'm not sure this default is still valid or not. Someone would >>> have to investigate. An alternative would be moving it into >>> node_reclaim_distance or somesuch. >>> >> >> Do you mean the following: >> >> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c >> index 444bdfdab731..436c899d8da2 100644 >> --- a/kernel/sched/topology.c >> +++ b/kernel/sched/topology.c >> @@ -1697,11 +1697,16 @@ sd_init(struct sched_domain_topology_level *tl, >>                  sd->cache_nice_tries = 2; >> >>                  sd->flags &= ~SD_PREFER_SIBLING; >> -               sd->flags |= SD_SERIALIZE; >>                  if (sched_domains_numa_distance[tl->numa_level] > >> node_reclaim_distance) { >>                          sd->flags &= ~(SD_BALANCE_EXEC | >>                                         SD_BALANCE_FORK | >>                                         SD_WAKE_AFFINE); >> +                       /* >> +                        * Nodes that are far away need to be >> serialized to >> +                        * reduce the overhead of long-distance task >> migration >> +                        * caused by load balancing. >> +                        */ >> +                       sd->flags |= SD_SERIALIZE; >>                  } >> >> We can launch some tests to see if removing SD_SERIALIZE would >> bring any impact. >> >>>> On a 2-socket Granite Rapids system with sub-NUMA clustering enabled >>>> and running OLTP workloads, 7.6% of CPU cycles were spent on cmpxchg >>>> operations for `sched_balance_running`. In most cases, the attempt >>>> aborts immediately after acquisition because the load balance time is >>>> not yet due. >>> >>> So I'm not sure I understand the situation, @continue_balancing should >>> limit this concurrency to however many groups are on this domain -- your >>> granite thing with SNC on would have something like 6 groups? >>> >> >> My understanding is that, continue_balancing is set to false after >> atomic_cmpxhg(sched_balance_running), so if sched_balance_domains() >> is invoked by many CPUs in parallel, the atomic operation still compete? >> > > From what i could remember, > > This mostly always happens at SMT after which continue_balancing = 0. > Since multiple CPUs end up calling it (specially on busy system) > it causes a lot cacheline bouncing. and ends up showing in perf profile. > I see, when reaching NUMA domain, the continue_balancing should already be set to 0. Thanks for pointing it out. thanks, Chenyu