From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from SA9PR02CU001.outbound.protection.outlook.com (mail-southcentralusazon11013030.outbound.protection.outlook.com [40.93.196.30]) (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 C6955369D7A for ; Tue, 14 Jul 2026 06:50:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.93.196.30 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784011805; cv=fail; b=a0b/ShviDk60Pamsrb5eBHrXy8+LuRhn4W7eL5202cgXFiFiCcjH2TdltUkXBgpoaT1KheYSPDnl893qSKtvscrnEGiodsPuxbtSkYhiZaiKPpLT2FnW8lChQUubeGCIk0EySN9bE5PJBalFCjy85y6Pxom+Nac1AwfmM3CdDVY= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784011805; c=relaxed/simple; bh=FVlZ3h5c13cUaWiNWELJmMsvyBygZxU4fbk7ey/0O1c=; h=Date:From:To:Cc:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:MIME-Version; b=aj3Xjh1benshnKXI2Fw2abkqxZxDga2ox1astNx5NAcanBXtXfYRiqtdFFY9Dv+Qd2tRlD8HEfy5sJqlKJYutALIJDLCu1LMJljoy3+5yOExrfO78hWNOfQKQsiD8ZIlpOXiy/ST1CBwDzZjcWYdsgB1+D3ZYVLbybmNYxV+dkQ= 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=UvsIYhb6; arc=fail smtp.client-ip=40.93.196.30 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="UvsIYhb6" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=cAN/zY+Jaj+Mq0MET+6LKBS/eKgveTXucCITLLx5hHYMvJEGVt7/IRrXEHJ7On67Eb0ZxmVl2aS6WCVpSSv3qfhUOdGt2tqIWAP+jlMAKZnZlt+egB/o8C3/KUbrnik1kpRs0k+KnaqIbfdbzbBpkU4wSUkrcMMldAsn7ZMrK/XWMpTvivJymZpa/U+HUoQNjXBRgqyaVssSw3EZoLU9SEBUERWA9HF3FcPleTy4NlPxyxW/ZIqy0qwdnrZ/t7IvMMvH7O+L2yY156FHJdPM5S5BeyZASWzEYQ4noOORHTddWrvMIugKu1xmm3eNx+l1hRW8DtXSFGk3HCwUIgw3Eg== 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=e0PO0qTpR6ex2rnHyRhVeCrlsEcmEuVwK9YJ7K/qbyQ=; b=dahMtAi8jbA2nO7UtPgGAA21u2ikhE3GB+cUeqDgbkLa6sUn/6x0UQHIdkr9QlBrxZTT8M823ga+G5vgBjch46Eem0LkGBv3B/Q7Xj/BHOOBKTK8kfl1VefMhQTRfMsbOroMoN+/D1m2SKrWa4NOHeJy2W8ORnjiuCTXwXBgCV2ghXztfbDIu8v6zshDn4Jrm5L9KSrBwf3X7TAhNVOJdHvouVyFqOwkBh3XxBNGN+UBgtaRebCj0i51lS6WW/OFgKrFEwF/Mfw/bwofy1N1pkBHwyjIjVwUCfmpJhJVy5AvypuLLvSIa5oLKuFPm5cwbBKN66Wr09y6Nvblw5Sb7g== 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=e0PO0qTpR6ex2rnHyRhVeCrlsEcmEuVwK9YJ7K/qbyQ=; b=UvsIYhb6R1XxZpvKGyl74MMDJPJqhb5B0HAIWnxILzyeGP3XfyIw9cgZQptn17JU7fkK6iv6zk1DTGfuIRN0WiEYkjY6Iq5F2EjD0g9F5Tt29r9BAs2xpbcdL/ooxRTK0we3ucWCP6BZO5n34G62y+Mm9St0AunqLMo92VCbyo4VKt9et8GObiXazb6zsKUMh3MDB6mA9kx8LtIhivd1+A21HGXk7SXm+LgIlwjkT8Gp0MfiMNiN9X4ThbSGYHPR6lU7e1VVQOsCEwAAOJIoqL7fgGT2QFtUs5OhtCioFQQtHr+zxTSYYBP19cijoz8gIOaRyfRO113J0kA5fxAlrQ== 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 SJ5PPF75EAF8F39.namprd12.prod.outlook.com (2603:10b6:a0f:fc02::999) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.181.22; Tue, 14 Jul 2026 06:49:57 +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 15.21.0202.014; Tue, 14 Jul 2026 06:49:57 +0000 Date: Tue, 14 Jul 2026 08:49:49 +0200 From: Andrea Righi To: Tejun Heo Cc: David Vernet , Changwoo Min , sched-ext@lists.linux.dev, Emil Tsalapatis , linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 sched_ext/for-7.3 18/33] sched_ext: Add reject DSQ for cap-rejected dispatches Message-ID: References: <20260709225041.1695495-1-tj@kernel.org> <20260709225041.1695495-19-tj@kernel.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260709225041.1695495-19-tj@kernel.org> X-ClientProxiedBy: MI1P293CA0023.ITAP293.PROD.OUTLOOK.COM (2603:10a6:290:3::9) To DM6PR12MB4827.namprd12.prod.outlook.com (2603:10b6:5:1d6::14) Precedence: bulk X-Mailing-List: sched-ext@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR12MB4827:EE_|SJ5PPF75EAF8F39:EE_ X-MS-Office365-Filtering-Correlation-Id: 959a5b9b-2858-4e61-d22d-08dee1741e25 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024|23010399003|11063799006|56012099006|4143699003|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)(366016)(376014)(1800799024)(23010399003)(11063799006)(56012099006)(4143699003)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?14uo/TLXkCq4v7fC1fAKcVWJtchyqF3tW9O2jkq7YA3uQoEhyPonS4BgUd5A?= =?us-ascii?Q?FnqdZ8blUFpzn7C/P09kIW0UzGUtmwIv5nHEha01UOm1ZzpYdvloJRBh5sNE?= =?us-ascii?Q?f96UyA0tWSyYEVAZLt+Aa+AXTzqnW1Nzm3egc3m1h/CkezsjWIxyvEhZ7D0o?= =?us-ascii?Q?5JPtdSLN9bW/ULseSi+CGYA9rOFaRibGRZYJ67tNE7isVEt+lF82XEULKS88?= =?us-ascii?Q?tpYp/1hNmAP5fsWsYuYVPTxtvRIvYGJhimUlfJOcH+23fXJV+Zhy+tirx5rY?= =?us-ascii?Q?aOLktTqQI3/RKKFek+BHaU/b/mMjEh1CEnIMyiJObUFzDX1Qz2awIxB/XCFK?= =?us-ascii?Q?sZeeQuRFoi1/p2n0uH+ALymS3XLIS3j4sdrZKBw09ngDi14b6vrMtZ8+l60R?= =?us-ascii?Q?l/lpuR82PFbGI0nI3HNQU5fkJ/ipyqmBzdAYW7TqwGMP3LDfqS6+0XgMOHPN?= =?us-ascii?Q?YFxaTcL0STxwKdm74ozFykLAr+N+9QTeFQBMwF5m+n+Q+GEfKafeQwjXv0kQ?= =?us-ascii?Q?kpznlWQF6+29Ybdy39PTUe6sQJ1QJxDyWSnvmotgXHPSxUD1EkwZmvIAHcaq?= =?us-ascii?Q?NoBAFEj4naTKtEyiH08PXF+WfwOH6UXzhDcyu+Go1U53CAhVFEce7kcLfKXN?= =?us-ascii?Q?2aSILxw3yRriFWuikRb1LJ3gync1LM6t1gIpWFj685vbTnafwIHpNWAnN7J4?= =?us-ascii?Q?Uql8faz3v/puE3JlCFrAknDWVpswIFOZKHzp//mrbW79o+fxM2IqcvY7r8sa?= =?us-ascii?Q?X4P1XRAgbqjNtJ1RvR50womztCroQ3xKcbhWblYgJW4xv/j9ipiC80AxexB3?= =?us-ascii?Q?nMHbaMNqGopgCfImjkZ7en718au9+LUAU3IhxvFxlGTq4tJ8ZgtmLqX69xuc?= =?us-ascii?Q?NUIpT489PgpEv8rvwNLyfkHLrhNNJyiETvtSTDDq85uyL0go8I4NwTRj4Yiz?= =?us-ascii?Q?cJojURQWkVZrrQk+6dhpPgw7dF7pYEGbvEeOsFC73bQSTdFnN8rUPo5J1g50?= =?us-ascii?Q?0EvKwr2fv/cVxaWZRJH3xnXK2HpE2XVDjy8IyKZXA7n7x35kmaWpHKCuwC/y?= =?us-ascii?Q?4tUM5+8P4svjV/tbXR9hEX1DOwuonznFBsQDvFEtFFovVgQyJe3+DLkjy/EI?= =?us-ascii?Q?2xvWi4OhndSpLKPZd77HaLLqBdy+696ZM0KXUN2HFTX4ZhypC8p9bACMKrR+?= =?us-ascii?Q?hwRGLPhvCH9qsg36Zjy3Lyx52LKNF9jA/Kyl/w7wuE538bBzWkjIij2tT6Qm?= =?us-ascii?Q?fqvwlnPBJAgbMpFRxHyHekWXroFBRlMAnLh8DZNS1k420AVwuHZgKlvDeLFx?= =?us-ascii?Q?bBkGCHe3HPF8e1BPN6tZM0eyCuDmaEGedXpOmWrBRW9LilxqXUONd1DJwn30?= =?us-ascii?Q?EAn9dnU+6+WktgHmUXaHMYIXK+rayTXM03J/bbYGg2EYX+xCBiKzUIBN+RD+?= =?us-ascii?Q?VUiYinHIlSLKC6/2AfZWCJ+84YKNCCGO8zJNijFNFtzgPTkzeL42lvqjBm2s?= =?us-ascii?Q?yZvDZdVFKhLH7V7HtQAscvAp9EZ0lyUcVRG/29xPe4jIoljvcAESpvAYmCoj?= =?us-ascii?Q?UUJiB+JeyVUZFV+1NxQUbNOzILSv7da1iO5RE8GIGTS6FPKyQR7Amao/p2ac?= =?us-ascii?Q?x0kRfYmOiwXSQKXciq4EXxgLRewu0DnokhTBPcMQrKdva/S8E8GY9gBmY98o?= =?us-ascii?Q?5a6oqmkldTBscajpsSlO2rvINNYkcbl7AM1VuSr8UiIfscAtQlf5B75O6NTy?= =?us-ascii?Q?vnn+lOYDgg=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 959a5b9b-2858-4e61-d22d-08dee1741e25 X-MS-Exchange-CrossTenant-AuthSource: DM6PR12MB4827.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Jul 2026 06:49:57.3354 (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: E2f+chGenyNeTh91P607ddyXhY3TcaSPnB/O6ufx4r4MVN+36zgKIzVoxHj0RUkL8iOI7WsR7BzwzJw2kE1Ozw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ5PPF75EAF8F39 Hi Tejun, On Thu, Jul 09, 2026 at 12:50:26PM -1000, Tejun Heo wrote: > When a sub-scheduler dispatches a task to a CPU it lacks the required > capability on, the task must be rejected rather than allowed to run. > > Add the machinery for that. Each rq gets a reject DSQ, a kernel-internal > holding queue that is never run and that the BPF scheduler cannot reach. An > insert that must be refused is diverted there instead of the local DSQ, and > a deferred requeue then hands the parked tasks back to the BPF scheduler to > re-decide. A cap revoke extends this to already-queued tasks. When the > revoke reaches the cpu's effective caps, the cpu scans its local DSQ and > reenqueues the tasks that no longer qualify. > > A migration-disabled task must run on its cpu, so a capless one is admitted > anyway and counted in the new SCX_EV_SUB_FORCED_ADMIT event. > > This is preparation for the actual sub-sched cap enforcement. The divert is > wired but inert here. > > v2: Admit offline-rq and migration_pending inserts to local, not reject. (sashiko AI) > > Signed-off-by: Tejun Heo > --- ... > @@ -1344,7 +1351,12 @@ static void scx_dispatch_enqueue(struct scx_sched *sch, struct rq *rq, > struct scx_dispatch_q *dsq, struct task_struct *p, > u64 enq_flags) > { > - bool is_rq_owned = dsq_is_rq_owned(dsq); > + bool is_rq_owned = false; > + > + if (dsq->id == SCX_DSQ_LOCAL) { > + dsq = scx_local_or_reject_dsq(sch, rq, p, &enq_flags); > + is_rq_owned = true; > + } With CONFIG_EXT_SUB_SCHED=y, this calls scx_local_or_reject_dsq() for every local DSQ insertion even when there are no sub-schedulers attached. It shouldn't be too bad, but the hot path still pays for the out-of-line call and the CID/capability bookkeeping. Maybe the same static key that I suggested for the ops.update_idle() case (PATCH 28/33) can be used here as well and we could do something like: if (!static_branch_unlikely(&scx_has_sub_scheds)) return &rq->scx.local_dsq; Thanks, -Andrea