From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from SN4PR0501CU005.outbound.protection.outlook.com (mail-southcentralusazon11011052.outbound.protection.outlook.com [40.93.194.52]) (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 E3AA12BD034 for ; Tue, 30 Sep 2025 08:58:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.93.194.52 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759222710; cv=fail; b=jbnuE259qedmuBBe/mob7vfzr3zWyC2K5iZPidN0jy6HsuLcIuDiHFiRaYmflashxWymb9W/k7oRmxhh0UgKlReBigUgtv2YOTP/+cRSQ4WTeEF8+T08ayHI4eLk+0NSraA5LsFIKZBBbKaE7hyBY1tVnIpaHnjO1ntfMyyXYgQ= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759222710; c=relaxed/simple; bh=nXM4QSe5W73st6ijAy++AWIbAtfxRBpt1R8OQ/+zMaw=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=bYb3gvgKJ6GKLb6lK/vixr0rG/dU93324/kYaPulbaz6ArPBhYypCwN0Zti+TPNFkv5F6OB7lU1v8TY78yXWmI223wIoN2t4tKWHBtJETfJ2R4uwt1lLiP0yMsu7quniIbRd7k6iWIN/yRZ3lrsgq/wc2STnpBacjTCkXwVGcNg= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com; spf=fail smtp.mailfrom=amd.com; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b=lezU/BG/; arc=fail smtp.client-ip=40.93.194.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=amd.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b="lezU/BG/" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=BVZXXYMuQiq2mX6kqUl41FqSuNdBzrEDl9P8cGqr5f0HWdA0jmLSonkIepUHnCuq6Z6LG2DpO8bhPPadhdrKqQKH9BLITwaLC5SrecXGWody5/YYXtggIIAAF3Wc2ktcZ9VSa370MY8Pb796XPX2GdpB/77zO+7xV91ndJyproSUUvqLFd4dQ0pu7t/H514mSRdlpc9hUZBunB7vFP4vbEZ3JY7kpRX5doN+GfRsscxVL4NrwIB2q6gheXJyyKEoo5V793MW8myejJ+XmILFDxFvSNiSqpP/2Ne/6u6QDrUlAlTZMY/HXXyIpA/1O5Razgu2Mi49VSBFlHiRgn3GYw== 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=Jc71GtAau20ErpurWBz8O9Q5k9f33lf99nm/KdgVhng=; b=sR6gevDdWYqSpZvhEEEMY3VTrdgIzfnhmceustndy3Dg9m8TudK6ekk2f39feHMVpCoUzQRB253PFvksUI9zSszo6P1CqTiQm3KccVmE7Af8qATKMh48ddILYMcZeU7CiLT21dvgn2hJuMjgbFpBjKtWde4fasThJNHSJ7oQHarM9avupsJ4VtE2Yk1TlZBPy1oULMguPZK+hoWsuCHwp5TGteACsLOt5Dah+9OrMoYdiSFs2fdaGN9gKNEaFVSnJPSn93otzVEDsBj0fAXsYS+ndySad3RVzPsz0cU+0RDVXphFNFfBLvNUc77bd1dmkonI+rBWIMXsmeRl/hdVzA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass (sender ip is 165.204.84.17) smtp.rcpttodomain=bytedance.com smtp.mailfrom=amd.com; dmarc=pass (p=quarantine sp=quarantine pct=100) action=none header.from=amd.com; dkim=none (message not signed); arc=none (0) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amd.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=Jc71GtAau20ErpurWBz8O9Q5k9f33lf99nm/KdgVhng=; b=lezU/BG/+rNLyD4kwT4VSDx8VK+Ys3L1jVL6n9yKVxK7BEkVzMdaQ2ddkp9OFuJ8S2ETL1vByMRwmYJqlJBD/oZKx9AYkkPdiw8OzmkHyzy01AGqnp8EFIbo74ZTAJrtgFB54KiBunZqC8WTpaES5MntASb1pdf1dcy3L7POuN0= Received: from SJ0PR03CA0093.namprd03.prod.outlook.com (2603:10b6:a03:333::8) by DM6PR12MB4282.namprd12.prod.outlook.com (2603:10b6:5:223::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9160.17; Tue, 30 Sep 2025 08:58:24 +0000 Received: from CO1PEPF000044F2.namprd05.prod.outlook.com (2603:10b6:a03:333:cafe::d1) by SJ0PR03CA0093.outlook.office365.com (2603:10b6:a03:333::8) with Microsoft SMTP Server (version=TLS1_3, cipher=TLS_AES_256_GCM_SHA384) id 15.20.9182.14 via Frontend Transport; Tue, 30 Sep 2025 08:58:24 +0000 X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 165.204.84.17) smtp.mailfrom=amd.com; dkim=none (message not signed) header.d=none;dmarc=pass action=none header.from=amd.com; Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C Received: from satlexmb07.amd.com (165.204.84.17) by CO1PEPF000044F2.mail.protection.outlook.com (10.167.241.72) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9160.9 via Frontend Transport; Tue, 30 Sep 2025 08:58:23 +0000 Received: from SATLEXMB06.amd.com (10.181.40.147) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.17; Tue, 30 Sep 2025 01:58:22 -0700 Received: from satlexmb08.amd.com (10.181.42.217) by SATLEXMB06.amd.com (10.181.40.147) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Tue, 30 Sep 2025 03:58:22 -0500 Received: from [10.136.33.166] (10.180.168.240) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Tue, 30 Sep 2025 01:58:16 -0700 Message-ID: <658734b1-b02b-4e04-8479-ed17eb42c1f2@amd.com> Date: Tue, 30 Sep 2025 14:28:16 +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/fair: Prevent cfs_rq from being unthrottled with zero runtime_remaining To: Aaron Lu CC: Valentin Schneider , Ben Segall , Peter Zijlstra , Chengming Zhou , Josh Don , Ingo Molnar , Vincent Guittot , Xi Wang , , Juri Lelli , Dietmar Eggemann , "Steven Rostedt" , Mel Gorman , Chuyi Zhou , Jan Kiszka , "Florian Bezdeka" , Songtang Liu , Chen Yu , Matteo Martelli , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Sebastian Andrzej Siewior References: <20250929074645.416-1-ziqianlu@bytedance.com> <7c93d622-49fe-4e99-8142-aed69d48aa8a@amd.com> <20250930075602.GA510@bytedance> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20250930075602.GA510@bytedance> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1PEPF000044F2:EE_|DM6PR12MB4282:EE_ X-MS-Office365-Filtering-Correlation-Id: a215df29-3e23-47ef-c7c6-08ddffff8343 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|82310400026|36860700013|7416014|376014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?dnlCZXJXL0ROMVRrVEtUMDRWMkt6N2x6b3dndFhUcWx1OTI0Q2xXL3RXeWpO?= =?utf-8?B?WkZjRFBqR0dwU3pXUTJuVDkybkliekVyZWFTTVRqUGIzaWlhZENMcFUrN3pC?= =?utf-8?B?WDFPZ2x0VFdqZEZjdGh6RWliTko0NlFjNHJoRFNzdFdvbXVRQjJVS3FkZVVm?= =?utf-8?B?d2JOQmZGVHJ6UE1PeHRqNjBta0ltVlZNY0w3SnZ6MHpiWElHbDVlSkY4UE45?= =?utf-8?B?U1FUY3J4OENBUFJhcm5qYmlVeUhUZU0rTVhYcUFJZUhNS3NDazdNMXZaUzY2?= =?utf-8?B?UHVQM3U4RDJaMmYyM0JqTVVrek9iaHgyeGZGSWYxbkRIUTFPeGhoaEsrUXNp?= =?utf-8?B?K2JWQ2FneWM2NnJJOUFIUzJmanhjU08rUjNZOFZTK1E3K3Rla2h3VVBJTzB5?= =?utf-8?B?OTlSWFovMWpOSlFEZmQ4T0dDVFZKdUl3aE5td2dIVU11RTdPQTZJZG02NS9D?= =?utf-8?B?WnJidmZmc1pxTW5qSFhHUXJ6VVhZcGVnQ0tORHIxV1ZnWjQ1cnFUbjZUNFBP?= =?utf-8?B?WHFOWEhOWnJxYmV5eWZ6TkVPZytEdmJrbmxQK2hFZ0RrRlR5UjM2NjJDN1FN?= =?utf-8?B?VjRYMlFVY3hqNGZ2L29QM0lKZlZ1MkZjY29sM1Z3OGtPREl2MThwSVV0MWtS?= =?utf-8?B?OVYxVEpITSttQlp0OFZwVDZ5QXFJQzJycjY5TEg4SXN3WnFLUEhlRFpDdENZ?= =?utf-8?B?MWtaUUd0Qk9vem03a0NVQXdaZTBGYm9aU1hESXFVWnU0NHM4UGNSd3FoeHhJ?= =?utf-8?B?ZHZIK25hZ3BQajFTc0lsbSsyVGpFZlBkUitXNUlDS1lTbWhES3V2dG95MTZK?= =?utf-8?B?Y0x5bW1XeVVDTy91OGxUdzVBbUNhMjFPNGZjK3RTVDM5SzY1MzZrNTUzWUR5?= =?utf-8?B?TXdRV2xNZGx4MXluSlRnNnh0a1ZoT2lGajl1S2dkdjRnd3FNVXMydGljZEFh?= =?utf-8?B?UjVMeTRZN1NiVHNENHo5bTQxM3lNWTB3cGhTUUF4cUlhcHVhZFJpVkREZ3Jm?= =?utf-8?B?TVNwQ3hBMGs3SXpabVBXTElqa2xaSGZmWjc4NmZlT1RyNjhRQ3d6aXBDUUhz?= =?utf-8?B?N3BsM0NZS1RLZkNWTnZ0RWl1ZmhrU2lwNXhlQVVMWWNIdEpxb1pleE9ZSUg1?= =?utf-8?B?KzZkeGF0WWdETlJQRXRjKzY1cjJzVnprZXN0aHJ3dFBmNW5CVFo4STQzeVN6?= =?utf-8?B?Y1lFUUhUMVBBNXhHUVk2aEl0eHhKUllIbFVqWUYwTldvQzVUS3NaR3NWRzRw?= =?utf-8?B?K045dE1VWXNnSVF2ZXNmM2QrditqbEpnL3JTUVdiR2duSFdUZno5M1Y1dTY4?= =?utf-8?B?NlUyN0E0alNGd3NrazU2N0pGdVhMN1o2Z1ZrSGtsbDAwd0czWHFTM1lqbTRk?= =?utf-8?B?bEZkV0d3SGk1R2VURDdSdVRVNFc4K29XV0JScjZLZUYwaXdaekpQSHZMVjBa?= =?utf-8?B?WElTWmZKUll3RkVRVnBheHB2YjJ0WElrd0dOMU1yeTVUSFBaWCtxWFRyeW1Q?= =?utf-8?B?dGUwMTE4RERHaXhVSmRvLzZkbVMwYWVWc04vYTZ1bG1kckRUVjRvUkt0aFhS?= =?utf-8?B?OE5xTFdmVDZUVVR1QVdtbkdEYitpSEduRm44clYyaWQzcFJ0VXJJRW9rdGRR?= =?utf-8?B?bS85bGRsTi9rTmVIQndMVjV4UUR0ZzhEcVEvSWpPRXprUHhabFNnV2JHaXg0?= =?utf-8?B?eENOcHA2a2xRdzNNS2RYV2tIZkNLS1AwcDA5NzdNem5vVC80YXMxR3Rvc3dS?= =?utf-8?B?dmY1KzNaaTFuWXM4aStBeHhQYTgwVDNmN1NJUk9RbVJCd1lZWW5Yc3AyZWVu?= =?utf-8?B?Z3V1SEJ6YUhrTzFaeVRONFVjaG4rd0dkWmxIS2Jtc2Uwc3c2ZmFOSm13Mldu?= =?utf-8?B?REs0OCtxMDNyYW1obnFJWjhLWEpXSHZNWEY1d0Nhb09XaW9PU01NWkRkYm5J?= =?utf-8?B?cityOU9JZlE0dTE0UkFFeTdZNDRrbGVJMlBsK082ZjM3amJJVzNRdFVnUVFK?= =?utf-8?B?VVJaUCtuUjVvYW9BOUtVMTRDOUo4Nk1LRjV2SElmZ1RTb3hKSUhxaU5uV2NR?= =?utf-8?B?QUpkUnFTMkVYT3RqUytsUDdIVmxCaEF1a0J1NFRNRTY4WlYvSzR3TkVxKzdF?= =?utf-8?Q?5hUc=3D?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(1800799024)(82310400026)(36860700013)(7416014)(376014);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Sep 2025 08:58:23.9109 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a215df29-3e23-47ef-c7c6-08ddffff8343 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=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CO1PEPF000044F2.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4282 Hello Aaron, On 9/30/2025 1:26 PM, Aaron Lu wrote: > On Mon, Sep 29, 2025 at 03:04:03PM +0530, K Prateek Nayak wrote: > ... ... >> Can we instead do a check_enqueue_throttle() in enqueue_throttled_task() >> if we find cfs_rq->throttled_limbo_list to be empty? >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 18a30ae35441..fd2d4dad9c27 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -5872,6 +5872,8 @@ static bool enqueue_throttled_task(struct task_struct *p) >> */ >> if (throttled_hierarchy(cfs_rq) && >> !task_current_donor(rq_of(cfs_rq), p)) { > /* > * Make sure to throttle this cfs_rq or it can be unthrottled > * with no runtime_remaining and gets throttled again on its > * unthrottle path. > */ >> + if (list_empty(&cfs_rq->throttled_limbo_list)) >> + check_enqueue_throttle(cfs_rq); > > BTW, do you think a comment is needed? Something like the above, not > sure if it's too redundant though, feel free to let me know your > thoughts, thanks. Now that I'm looking at it again, I think we should actually do a: for_each_entity(se) check_enqueue_throttle(cfs_rq_of(se)); The reason being, we can have: root -> A (throttled) -> B -> C Consider B has runtime_remaining = 0, and subsequently a throttled task is queued onto C. Ideally, we should start the B/W timer for B at that point but we bail out after queuing it on C. Thoughts? Since we only catch up to the 0 runtime_remaining point, it should be fine. The comment can perhaps be something like: /* * If this is the first enqueue on throttled hierarchy, * ensure bandwidth is available when the hierarchy is * unthrottled. check_enqueue_throttle() will ensure * either some bandwidth is available, or will throttle * the cfs_rq and queue the bandwidth timer. */ > >> list_add(&p->throttle_node, &cfs_rq->throttled_limbo_list); >> return true; >> } >> --- -- Thanks and Regards, Prateek