From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from CH5PR02CU005.outbound.protection.outlook.com (mail-northcentralusazon11012066.outbound.protection.outlook.com [40.107.200.66]) (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 E3D05322A1F for ; Tue, 28 Jul 2026 15:45:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.200.66 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785253548; cv=fail; b=eDbd/NBony8/LXLgUqg0nja2k/rpXspSkkQ9QkfF9mBGT6Z+JnpsKjr0++SDlgYIzHylhIw6LtDu8Td11i0EgDvKQa3aKxQ/kRV1nEElfqZ+m62MpDnIjqWihPBSTq/XAfi6lSGs7fJlRLu1rXB5qJQHJE5Mg5xYNoKqtXxjdD0= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785253548; c=relaxed/simple; bh=RSFrbsojGcZtbuUs3GT7+QKSrVLaeSS7H4MfeGyBRjA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: Content-Type:MIME-Version; b=AbM7EcMI2CYY/LHajTMBR2njye05dZTK5033loBaTzInlurBcQZGZnaedyay/xc3qYZTlA1qWTXVaE8SFlbPdcQi357EY8Ktzp/KEskBaD4/rN4wG3ypNRj7/1NlHy1Cyd+LmhT0DwJhLSaxMQ6Ci3h1AjL7e3m2QfgTvbU3pkA= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=p+GcUS/n; arc=fail smtp.client-ip=40.107.200.66 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="p+GcUS/n" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=Q42EB/HPSZVSLJ1DdrLniFeguaCRKtoT4N3+v7tgx6iF/0lb4hypyzwR2HvtDtV+GlYxK9iH3aoO6/5D9fIE9QGzMCq2F2nqMscu+jOfyhxSYQYUlZIaSH0FEB3wAI2cL3ZkeblE8kLDq22EM8iTfuCguBybKDRF2X/JVftU2TtZKx51+yQ7ufeIDBP8FWGLz55qqnWloy6kekjeINIl/JWcmcluFsJyuUob46emfdcyv+90oSO+w0wT3uHDDW2C64Y5ya6uyXlSiAsXA0rQ7/ZSKXjslSn9M6nOfHmk9dad0HSQDghhP/7yJa48jvNfFU1l9z+0PaUbyNTs+JQsDw== 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=MtFz0AVf6UfKP/Sakkw9RPsa1SBJFbnhgKBEPT+7pCM=; b=m2L9RJhvN4e2jefXhz61HZCCaHOkZCZxQi0E6yZkN99SK1pxLfvKcMjgQZimNeTKz4WwP/bttjWjYeAIvqD0MOpp3MQIIk6sVgTepLt2AM0fALjat910Q8+a7acmsLi/7rlgpAg0fUH06OJ1RVPg7D6YOkSVrKf8X15teyS/JamNiumHN8nlgOktUvpK88yDthJVve2QhopPy1TufcgDKfONPTgdvdShmes4ntMEfWT5gspQE14DRYbauI7nqBxbhcWuQR4Q0f97Dxn6Xp+EUlhsd7ZI5DZoE2pdClZqPHijQ4lYGfTtA/RdhQZUqTVNbiF8A4z2TiSrnECQOvKtkQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=MtFz0AVf6UfKP/Sakkw9RPsa1SBJFbnhgKBEPT+7pCM=; b=p+GcUS/nuTjZaaMy3Yd0yFJAgb4MxhYR2x+c6uNJOl94xSBmMDWVlkbNAVGDG5ErEdr6YhFJXHW74lKZ8wbnrr2JGqDlvqI9TrpHN2BWmKow1icuaAv3BdaAf9uCmJgKH0aURmDL09UtLyPDPaq0wgXyOTWyNtroDVRomrHQElT4nDbIXoX8cGPfM5alRRG4e5DG0KIRVtlOJ/eyiEUqwb8Q6JNjgr7VrA13XMenh1DjfdJ2/M8UcG5iNE6HJ0zr/ZpPu4HKJM0R7yvYV5Ct4VvM9u3G82sxeFtLyFU2eHm5/+Nbui+89a8pyf3f6OabsbeQG3uZ1FCzALBes9ycCA== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from DM6PR12MB4827.namprd12.prod.outlook.com (2603:10b6:5:1d6::14) by SN7PR12MB7023.namprd12.prod.outlook.com (2603:10b6:806:260::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.245.13; Tue, 28 Jul 2026 15:45:37 +0000 Received: from DM6PR12MB4827.namprd12.prod.outlook.com ([fe80::6261:3040:864b:159c]) by DM6PR12MB4827.namprd12.prod.outlook.com ([fe80::6261:3040:864b:159c%5]) with mapi id 15.21.0245.012; Tue, 28 Jul 2026 15:45:37 +0000 From: Andrea Righi To: Tejun Heo , David Vernet , Changwoo Min , John Stultz Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Christian Loehle , David Dai , Koba Ko , Aiqun Yu , Shuah Khan , sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [PATCH 11/15] sched_ext: Split curr|donor references properly Date: Tue, 28 Jul 2026 17:43:29 +0200 Message-ID: <20260728154425.1549660-12-arighi@nvidia.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260728154425.1549660-1-arighi@nvidia.com> References: <20260728154425.1549660-1-arighi@nvidia.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: BY1P220CA0007.NAMP220.PROD.OUTLOOK.COM (2603:10b6:a03:59d::13) To DM6PR12MB4827.namprd12.prod.outlook.com (2603:10b6:5:1d6::14) 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: DM6PR12MB4827:EE_|SN7PR12MB7023:EE_ X-MS-Office365-Filtering-Correlation-Id: 380b1d83-aa13-41e6-8827-08deecbf44cb X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|366016|1800799024|376014|7416014|5023799004|11063799006|10067099003|56012099006|6133799003|22082099003|18002099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM6PR12MB4827.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(23010399003)(366016)(1800799024)(376014)(7416014)(5023799004)(11063799006)(10067099003)(56012099006)(6133799003)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?0c90VbYVCThCsJOfU71wWyq9Pm6+fnJaeW22V6guFuaIB34j9wfD0MM+A11M?= =?us-ascii?Q?Uq8lEOQoXQPCkDTzFb+MuI0fFC09SdPW3Ijg9pkDWpXAHdHLdBYKrHcsZTKm?= =?us-ascii?Q?t3+Wc+1tC/RhBc3PS7hUBHJVbPKFO2fZuhmKANcr+Cdc1L8QQY5ulEmSb3Es?= =?us-ascii?Q?e7JUQLJNEtemt3hKN6roPJOTxsZ0THy2PfwqcGh25bI3bzDHTuXBSlEFICsL?= =?us-ascii?Q?XWVh9bYaUhwQqV284K9eutKxS8AhmuM7VnN/zxwlNnSUaQU8RyhEnLUt9jmk?= =?us-ascii?Q?BbB3FptxaH8KUqBYJmjSHKRX6ITHEjDWlVFGH+Sgl79xs9G8b/+TwsGBRQPd?= =?us-ascii?Q?k/M2mU4k891y8NYCBLF6+RiBhG1N/J1Qy3uB6bTnc+gGEsknWrF2LK3RwUkk?= =?us-ascii?Q?OG1SOFGnGx/EMf/Klc/x44By1AaHKl+dRo3a32CC4oKb2gBN09FwT3FuNRX2?= =?us-ascii?Q?hA9gkbHDJMORQ9kqyn8bIV98yvSHBE8XxYGQL+tPc6pGgUe81F8QULS8N3Zg?= =?us-ascii?Q?w/20Rt0GFUxohUhBTUn2YqiEMncgd5uqVxiWuhlOb2UCJC2uIzY/KUvS0bQ0?= =?us-ascii?Q?llCGgwe54AGRmWq3d/cqUTsyx68Okz7ta0Lxyo+Fikm6WGpcA7jiaAzDlBEG?= =?us-ascii?Q?sUqz1p/Eo8p5RME6Eu565sj5DVEe4AO0P1t5prhpSt5+hMg0Gnw+d9RgkC0b?= =?us-ascii?Q?Z4HdZPTucXOVhZmJPO/c3mY0QbXRPWbbTmWKvepZvIclARe9a3p7fYDCUqn3?= =?us-ascii?Q?OmN1tyidQRh4CJEjKNKw2A+gqG0g80oltRG9PHMPWOZGfWON5tL7nCWvB3RC?= =?us-ascii?Q?qwfK7m0e7NJ30xxWO8FaapwQBWGs73TvzKnUZhj5xk9JvkH5LRwaR3kzgd7j?= =?us-ascii?Q?uLyz83dAUB9xurbEZqhT/yMO2Dx60wKQNz4uBp+KkhQYN1SqB6739UjYcPB9?= =?us-ascii?Q?NFaWsGxIPPKiD3Or0IFW7lkGBbpJ0I8CJZx+pjT71+mGIdFBHOLi4+jj7rTD?= =?us-ascii?Q?y4vIXusaIU0tWHS4cEOivZ33iqhJAjhQpSOsJujvNBv6AAoNBHhLzDwqC7wf?= =?us-ascii?Q?JXZDEHbyYru74H5UzLzdGL49/AH/12HeAyMyqED67rc4v/B30LwLsU8+PhrD?= =?us-ascii?Q?lPa8qHoB/HcTKg3faeTnaMKcsEq8CFDH4+CFGFqMQTt3AOKTvAOkXylQITCX?= =?us-ascii?Q?Spr+cGOMFE2zj1J15mfYMb7yt86ydME/PbED+SikGjUrbZNiIPSxIgZqwlnE?= =?us-ascii?Q?fns/1LKWUS4liRpfU3G6hgOgYX/NAjL84WUJZ5AEw2co+/fkWM4QhKdX3SWe?= =?us-ascii?Q?HXaxdUWtW3EDZFw4aeLzpwh7nLd3W+SP2VIZHAF3WPBekxV5EagXJjrJTY5k?= =?us-ascii?Q?iTk6E6NBrwXbD3XBgOX21RT7sAtopUh5iZ05hPMuAF92c+aY6qHm769nFxYi?= =?us-ascii?Q?XsOYRqhEiAgiVExCaQ7Wj6bHmPcj3/jGLUp7uBGIN0y49RyHS+ylp5fjyHSw?= =?us-ascii?Q?9GyRdiiW73l+LaqmDe9LpJpf8QBXhQIzugIC0Y1Qq8nzBJ4rG2XY3vk96Ax6?= =?us-ascii?Q?9ElvLq7s9+WtAFeSc0Qdb2H79/rHO4nHKRhYTvBTFywAdvXfxryWDT5w5FeY?= =?us-ascii?Q?MLtdABlZktmiK3QngZf3px5rD8J6Qt9FnJ2smHze2qXCTm877B9zxAPxpdHh?= =?us-ascii?Q?RIu/GD+e2waqR6zVERBSDDiEp6igEEjSn+tjFPVaOnO5VCi4zzL+jEqYn/mN?= =?us-ascii?Q?B6kdrY0WuA=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 380b1d83-aa13-41e6-8827-08deecbf44cb X-MS-Exchange-CrossTenant-AuthSource: DM6PR12MB4827.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jul 2026 15:45:37.2405 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: DnAZczeeUQxgjYZrnE9/pIuItUl+0MfJ0veVk0Tcpm0NAAjlAsHnvMxXwchQXcmcV54WfcNZLWhFy2khE8znPQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB7023 With proxy execution, the task selected by the scheduler and the task physically executing can differ. A blocked mutex waiter donates its scheduling context to the lock owner: D -----------------> M -------------> O ----------------> T [donor] blocked on [mutex] owned by [owner] preempted by [task] \_________________________________^ donates scheduling context where: D = blocked donor M = mutex O = mutex owner T = competing runnable task During a proxy execution switch, D supplies the scheduling class, priority, and runtime budget, while O supplies the execution context: O is the task whose code physically executes. T is a competing runnable task which may preempt the D/O proxy execution. Consider FAIR and EXT tasks with sched_ext running in partial mode. FAIR can be replaced with a higher scheduling class such as RT or deadline without changing the class interaction described here. The possible combinations are: 1. D is EXT, O is EXT, T is EXT D can interrupt T according to BPF scheduling policy. O executes with D's EXT priority and runtime budget, while T waits in EXT. 2. D is EXT, O is EXT, T is FAIR D is visible to the BPF scheduler, but cannot preempt T because EXT is below FAIR. Once T stops, BPF can dispatch D and O executes with D's EXT priority and runtime budget. If T becomes runnable again, it preempts the D/O proxy execution. 3. D is EXT, O is FAIR, T is EXT This cannot represent T preempting O because EXT is below FAIR. 4. D is EXT, O is FAIR, T is FAIR D cannot boost O above T because EXT is below FAIR. O and T continue competing under FAIR. Once O releases M, D wakes and resumes normal EXT scheduling. 5. D is FAIR, O is EXT, T is EXT D preempts T as the higher-class scheduling context. O executes with D's FAIR priority and runtime budget, while T waits in EXT. D is not visible to the BPF scheduler. 6. D is FAIR, O is EXT, T is FAIR D competes with T according to its FAIR deadline. When D is selected, O executes with D's FAIR priority and runtime budget. D is not visible to the BPF scheduler. 7. D is FAIR, O is FAIR, T is EXT This cannot represent T preempting O because EXT is below FAIR. 8. D is FAIR, O is FAIR, T is FAIR O, T, and D all have FAIR scheduling contexts. D remains runnable as a blocked proxy donor. When CFS selects D, O executes using D's FAIR scheduling context. When CFS selects O, O executes using its own FAIR context, and when CFS selects T, T executes normally. D is not visible to the BPF scheduler. Thus, sched_ext policy and accounting must generally use rq->donor, the scheduler-selected task which supplies the scheduling context, rather than rq->curr, the task whose code physically executes. Without proxy execution they are the same task. On nohz_full CPUs, a blocked proxy donor must retain the scheduler tick even when it has an infinite slice. Otherwise, a full dynticks CPU could stop the tick while rq->curr and rq->donor differ, violating assumptions made by the remote NOHZ tick path. This is a conservative compromise that keeps the change local to sched_ext, at the cost of a periodic tick while a blocked proxy donor is selected. Allowing blocked proxy donors to run tickless would require making the core scheduler's remote tick handling aware that rq->curr and rq->donor can differ. Moreover, extend scx_dump_state() to report both contexts. Each CPU record now includes a donor= line. If an EXT donor differs from rq->curr, also emit its detailed task record. The existing '*' marker continues to identify rq->curr, while the donor= line identifies the otherwise unmarked donor record. Note that at this point in the series, CONFIG_SCHED_PROXY_EXEC still depends on !CONFIG_SCHED_CLASS_EXT, so proxy execution and sched_ext cannot be enabled together. The scheduling changes are therefore preparatory. A later patch removes this restriction. Co-developed-by: John Stultz Signed-off-by: John Stultz Signed-off-by: Andrea Righi --- Documentation/scheduler/sched-ext.rst | 6 ++ kernel/sched/ext/ext.c | 115 +++++++++++++++++--------- kernel/sched/ext/sub.h | 8 +- 3 files changed, 86 insertions(+), 43 deletions(-) diff --git a/Documentation/scheduler/sched-ext.rst b/Documentation/scheduler/sched-ext.rst index ad2fff3c05937..db1ef89ed8f2a 100644 --- a/Documentation/scheduler/sched-ext.rst +++ b/Documentation/scheduler/sched-ext.rst @@ -487,6 +487,12 @@ and edge cases, to name a few examples: class, in which case it will exit the tick-dispatch loop even though it is runnable and has a non-zero slice. +* Under proxy execution, sched_ext continues to observe the donor as the current + scheduling context. A blocked donor does not enter an ``ops.running()`` / + ``ops.stopping()`` session because it does not execute itself, and the lock + owner executing on its behalf is intentionally not reported through these + callbacks. + See the "Scheduling Cycle" section for a more detailed description of how a freshly woken up task gets on a CPU. diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c index 3fe66298d1811..5dbf89debc6c7 100644 --- a/kernel/sched/ext/ext.c +++ b/kernel/sched/ext/ext.c @@ -1336,20 +1336,27 @@ static void apply_task_slice_oob(struct rq *rq, struct task_struct *p) static void update_curr_scx(struct rq *rq) { - struct task_struct *curr = rq->curr; + struct task_struct *donor; s64 delta_exec; + /* + * update_curr_scx() is selected through rq->donor->sched_class, not + * rq->curr->sched_class, so @donor is always an EXT task here. If an EXT + * owner executes for a FAIR donor, FAIR's update_curr() runs instead. + */ + donor = rq->donor; + /* apply even on 0 delta_exec, callers may still act on the slice */ - apply_task_slice_oob(rq, curr); + apply_task_slice_oob(rq, donor); delta_exec = update_curr_common(rq); if (unlikely(delta_exec <= 0)) return; - if (curr->scx.slice != SCX_SLICE_INF) { - curr->scx.slice -= min_t(u64, curr->scx.slice, delta_exec); - if (!curr->scx.slice) - touch_core_sched(rq, curr); + if (donor->scx.slice != SCX_SLICE_INF) { + donor->scx.slice -= min_t(u64, donor->scx.slice, delta_exec); + if (!donor->scx.slice) + touch_core_sched(rq, donor); } dl_server_update(&rq->ext_server, delta_exec); @@ -1525,9 +1532,9 @@ static void rq_owned_post_enq(struct scx_sched *sch, struct rq *rq, if (rq->scx.flags & SCX_RQ_IN_BALANCE) return; - if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr && - rq->curr->sched_class == &ext_sched_class) { - set_task_slice(rq->curr, 0); + if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->donor && + rq->donor->sched_class == &ext_sched_class) { + set_task_slice(rq->donor, 0); resched_curr(rq); } } @@ -2090,13 +2097,14 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int core_enq_ rq->scx.flags |= SCX_RQ_IN_WAKEUP; /* - * Restoring a running task will be immediately followed by - * set_next_task_scx() which expects the task to not be on the BPF + * Restoring the current scheduling context will be immediately followed + * by set_next_task_scx() which expects the task to not be on the BPF * scheduler as tasks can only start running through local DSQs. Force * direct-dispatch into the local DSQ by setting the sticky_cpu. Mark * IGNORE_CAPS to force entry into the local DSQ. */ - if (unlikely(enq_flags & ENQUEUE_RESTORE) && task_current(rq, p)) { + if (unlikely(enq_flags & ENQUEUE_RESTORE) && + task_current_donor(rq, p)) { sticky_cpu = cpu_of(rq); enq_flags |= SCX_ENQ_IGNORE_CAPS; } @@ -2812,7 +2820,8 @@ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq, } /* if the destination CPU is idle, wake it up */ - if (!fallback && sched_class_above(p->sched_class, dst_rq->curr->sched_class)) + if (!fallback && sched_class_above(p->sched_class, + dst_rq->donor->sched_class)) resched_curr(dst_rq); } @@ -3036,6 +3045,8 @@ static void scx_start_task_running(struct rq *rq, struct task_struct *p) static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first) { + bool can_stop_tick; + if (p->scx.flags & SCX_TASK_QUEUED) { /* * Core-sched might decide to execute @p before it is @@ -3060,6 +3071,7 @@ static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first) /* apply any pending out-of-band slice request before the tick decision */ apply_task_slice_oob(rq, p); + can_stop_tick = p->scx.slice == SCX_SLICE_INF && !p->is_blocked; /* * @p is getting newly scheduled or got kicked after someone updated its @@ -3070,7 +3082,7 @@ static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first) * nohz. In the future, we might want to add a mechanism to update * load_avgs periodically on tick-stopped CPUs. */ - if (p->scx.slice == SCX_SLICE_INF) { + if (can_stop_tick) { if (!(rq->scx.flags & SCX_RQ_CAN_STOP_TICK)) { /* * Bypass mode always assigns finite slices, so @p @@ -3091,7 +3103,8 @@ static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first) /* * @rq still references the outgoing scheduling context. A finite - * slice is sufficient by itself to require the tick. + * slice or a blocked proxy donor is sufficient by itself to require + * the tick. */ if (tick_nohz_full_cpu(cpu_of(rq))) tick_nohz_dep_set_cpu(cpu_of(rq), TICK_DEP_BIT_SCHED); @@ -3280,7 +3293,7 @@ static struct task_struct *first_local_task(struct rq *rq) static struct task_struct * do_pick_task_scx(struct rq *rq, struct rq_flags *rf, bool force_scx) { - struct task_struct *prev = rq->curr; + struct task_struct *prev = rq->donor; bool keep_prev; struct task_struct *p; @@ -3679,9 +3692,9 @@ void scx_tick(struct rq *rq) update_other_load_avgs(rq); } -static void task_tick_scx(struct rq *rq, struct task_struct *curr, int queued) +static void task_tick_scx(struct rq *rq, struct task_struct *donor, int queued) { - struct scx_sched *sch = scx_task_sched(curr); + struct scx_sched *sch = scx_task_sched(donor); update_curr_scx(rq); @@ -3690,13 +3703,13 @@ static void task_tick_scx(struct rq *rq, struct task_struct *curr, int queued) * we can't trust the slice management or ops.core_sched_before(). */ if (scx_bypassing(sch, cpu_of(rq))) { - set_task_slice(curr, 0); - touch_core_sched(rq, curr); + set_task_slice(donor, 0); + touch_core_sched(rq, donor); } else if (SCX_HAS_OP(sch, tick)) { - SCX_CALL_OP_TASK(sch, tick, rq, curr); + SCX_CALL_OP_TASK(sch, tick, rq, donor); } - if (!curr->scx.slice) + if (!donor->scx.slice) resched_curr(rq); } @@ -4335,16 +4348,16 @@ static u32 reenq_local(struct scx_sched *sch, struct rq *rq, u64 reenq_flags) } /* - * The revoke that scheduled this scan may have raced the pick: curr + * The revoke that scheduled this scan may have raced the pick: donor * may be a now-capless task, either one that kept running or one * promoted off the local DSQ between the ecaps sync and this scan. * Zero the slice to evict it. The enqueue gate blocks new capless * inserts, so no later pick can slip through after the scan. */ if ((reenq_flags & SCX_REENQ_CAP_REVOKE) && - rq->curr->sched_class == &ext_sched_class && - scx_task_reenq_on_cap_revoke(rq, rq->curr)) { - set_task_slice(rq->curr, 0); + rq->donor->sched_class == &ext_sched_class && + scx_task_reenq_on_cap_revoke(rq, rq->donor)) { + set_task_slice(rq->donor, 0); resched_curr(rq); } @@ -4581,14 +4594,18 @@ static void run_deferred(struct rq *rq) #ifdef CONFIG_NO_HZ_FULL bool scx_can_stop_tick(struct rq *rq) { - struct task_struct *p = rq->curr; + struct task_struct *p = rq->donor; struct scx_sched *sch = scx_task_sched(p); + /* The remote tick path assumes that proxy execution is not active. */ + if (rq->curr != rq->donor) + return false; + if (p->sched_class != &ext_sched_class) return true; /* - * @rq->curr may still reference an outgoing EXT task after it has been + * @rq->donor may still reference an outgoing EXT task after it has been * dequeued. If no EXT tasks are accounted on @rq, ignore its stale * slice state. If another task is dispatched from a DSQ, * set_next_task_scx() will update the dependency for the incoming task. @@ -4602,7 +4619,8 @@ bool scx_can_stop_tick(struct rq *rq) /* * @rq can dispatch from different DSQs, so we can't tell whether it * needs the tick or not by looking at nr_running. Allow stopping ticks - * iff the BPF scheduler indicated so. See set_next_task_scx(). + * iff set_next_task_scx() determined that the selected scheduling context + * can run tickless. */ return rq->scx.flags & SCX_RQ_CAN_STOP_TICK; } @@ -6796,6 +6814,9 @@ static void scx_dump_cpu(struct scx_sched *sch, struct seq_buf *s, dump_line(&ns, " curr=%s[%d] class=%ps", rq->curr->comm, rq->curr->pid, rq->curr->sched_class); + dump_line(&ns, " donor=%s[%d] class=%ps", + rq->donor->comm, rq->donor->pid, + rq->donor->sched_class); if (!cpumask_empty(pcpu->cpus_to_kick)) dump_line(&ns, " cpus_to_kick : %*pb", cpumask_pr_args(pcpu->cpus_to_kick)); @@ -6839,6 +6860,10 @@ static void scx_dump_cpu(struct scx_sched *sch, struct seq_buf *s, if (rq->curr->sched_class == &ext_sched_class && (dump_all_tasks || scx_task_on_sched(sch, rq->curr))) scx_dump_task(sch, s, dctx, rq, rq->curr, '*'); + if (rq->donor != rq->curr && + rq->donor->sched_class == &ext_sched_class && + (dump_all_tasks || scx_task_on_sched(sch, rq->donor))) + scx_dump_task(sch, s, dctx, rq, rq->donor, ' '); list_for_each_entry(p, &rq->scx.runnable_list, scx.runnable_node) if (dump_all_tasks || scx_task_on_sched(sch, p)) @@ -8367,7 +8392,7 @@ static bool kick_one_cpu(s32 cpu, struct scx_sched_pcpu *pcpu, struct rq *this_r unsigned long flags; raw_spin_rq_lock_irqsave(rq, flags); - cur_class = rq->curr->sched_class; + cur_class = rq->donor->sched_class; /* * During CPU hotplug, a CPU may depend on kicking itself to make @@ -8385,7 +8410,7 @@ static bool kick_one_cpu(s32 cpu, struct scx_sched_pcpu *pcpu, struct rq *this_r if (cur_class == &ext_sched_class) { if (likely(!scx_missing_caps(pcpu->sch, cpu, scx_caps_for_preempt(pcpu->sch, rq)))) - set_task_slice(rq->curr, 0); + set_task_slice(rq->donor, 0); else __scx_add_event(pcpu->sch, SCX_EV_SUB_PREEMPT_DENIED, 1); @@ -9360,13 +9385,15 @@ __bpf_kfunc bool scx_bpf_task_set_slice(struct task_struct *p, u64 slice, return false; /* - * Directly write only when we hold the lock of the rq @p is queued or - * running on. See the slice write rules above. + * Directly write only when we hold the lock of the rq @p is queued on or + * provides the current scheduling context for. Under proxy execution, + * rq->donor owns and consumes the slice while rq->curr executes on its + * behalf. See the slice write rules above. */ locked_rq = scx_locked_rq(); if (!locked_rq || (READ_ONCE(p->scx.runnable_cpu) != cpu_of(locked_rq) && - !task_current(locked_rq, p))) { + !task_current_donor(locked_rq, p))) { set_task_slice_oob(sch, p, slice); return true; } @@ -10251,12 +10278,17 @@ __bpf_kfunc void scx_bpf_put_cpumask(const struct cpumask *cpumask) } /** - * scx_bpf_task_running - Is task currently running? + * scx_bpf_task_running - Is task the current scheduling context? * @p: task of interest + * + * Under proxy execution, this reports the donor rather than the task whose + * code is physically executing. The physical execution context is intentionally + * not exposed to the BPF scheduler, which continues to observe the donor as the + * running scheduling context. */ __bpf_kfunc bool scx_bpf_task_running(const struct task_struct *p) { - return task_rq(p)->curr == p; + return rcu_access_pointer(task_rq(p)->donor) == p; } /** @@ -10317,10 +10349,15 @@ __bpf_kfunc struct rq *scx_bpf_locked_rq(const struct bpf_prog_aux *aux) } /** - * scx_bpf_cpu_curr - Return remote CPU's curr task + * scx_bpf_cpu_curr - Return remote CPU's current scheduling context * @cpu: CPU of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * + * Under proxy execution, this returns the donor, which supplies the scheduling + * policy and runtime budget, rather than the task whose code is physically + * executing. The physical execution context is intentionally not exposed to + * the BPF scheduler. + * * Callers must hold RCU read lock (KF_RCU). */ __bpf_kfunc struct task_struct *scx_bpf_cpu_curr(s32 cpu, const struct bpf_prog_aux *aux) @@ -10336,7 +10373,7 @@ __bpf_kfunc struct task_struct *scx_bpf_cpu_curr(s32 cpu, const struct bpf_prog_ if (!scx_cpu_valid(sch, cpu, NULL)) return NULL; - return rcu_dereference(cpu_rq(cpu)->curr); + return rcu_dereference(cpu_rq(cpu)->donor); } /** @@ -10360,7 +10397,7 @@ __bpf_kfunc struct task_struct *scx_bpf_cid_curr(s32 cid, const struct bpf_prog_ cpu = scx_cid_to_cpu(sch, cid); if (cpu < 0) return NULL; - return rcu_dereference(cpu_rq(cpu)->curr); + return rcu_dereference(cpu_rq(cpu)->donor); } /** diff --git a/kernel/sched/ext/sub.h b/kernel/sched/ext/sub.h index b5870aeb9c625..0579e32015d17 100644 --- a/kernel/sched/ext/sub.h +++ b/kernel/sched/ext/sub.h @@ -153,14 +153,14 @@ static inline u64 scx_caps_for_task(struct task_struct *p) return SCX_CAP_ENQ; } -/* the cap @sch needs to preempt @rq's current task, 0 if none */ +/* the cap @sch needs to preempt @rq's current scheduling context, 0 if none */ static inline u64 scx_caps_for_preempt(struct scx_sched *sch, struct rq *rq) { - struct task_struct *curr = rq->curr; + struct task_struct *donor = rq->donor; /* a non-ext task can't be preempted by ext, own-subtree needs no cap */ - if (curr->sched_class != &ext_sched_class || - scx_is_descendant(scx_task_sched(curr), sch)) + if (donor->sched_class != &ext_sched_class || + scx_is_descendant(scx_task_sched(donor), sch)) return 0; return SCX_CAP_PREEMPT; } -- 2.55.0