From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 87C5CCCD194 for ; Thu, 16 Oct 2025 10:05:38 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.1144385.1477776 (Exim 4.92) (envelope-from ) id 1v9KrP-0000IX-5n; Thu, 16 Oct 2025 10:05:27 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 1144385.1477776; Thu, 16 Oct 2025 10:05:27 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1v9KrP-0000IQ-2l; Thu, 16 Oct 2025 10:05:27 +0000 Received: by outflank-mailman (input) for mailman id 1144385; Thu, 16 Oct 2025 10:05:26 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1v9KrO-0000I6-0h for xen-devel@lists.xenproject.org; Thu, 16 Oct 2025 10:05:26 +0000 Received: from SJ2PR03CU001.outbound.protection.outlook.com (mail-westusazlp170120002.outbound.protection.outlook.com [2a01:111:f403:c001::2]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id a0b5d31b-aa77-11f0-980a-7dc792cee155; Thu, 16 Oct 2025 12:05:23 +0200 (CEST) Received: from DM6PR03MB5227.namprd03.prod.outlook.com (2603:10b6:5:247::22) by DM6PR03MB5161.namprd03.prod.outlook.com (2603:10b6:5:240::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9228.12; Thu, 16 Oct 2025 10:05:20 +0000 Received: from DM6PR03MB5227.namprd03.prod.outlook.com ([fe80::c9a0:563d:c344:aec2]) by DM6PR03MB5227.namprd03.prod.outlook.com ([fe80::c9a0:563d:c344:aec2%5]) with mapi id 15.20.9228.012; Thu, 16 Oct 2025 10:05:20 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: a0b5d31b-aa77-11f0-980a-7dc792cee155 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=BGopSH8/JnEGuqj6xKQsxKb/9HlxEOUh6HF6DBXgYh97jn6nesmKO77GfMgX+ULCCHb/pya99f124ON2cYchL7iq1v3aYw95Ozw3XPiQEkbkAkG2FOdNVy+8QveqX3nk+Z0ZOuZe2OGuLZclksI0PfOsXD50LAuE1wAgmxuc9bxZX0dBRcRiKJY/XFqthPfZlhR4ujB546LJAoyt/RWWaD5Ur4yHIZyQmRSltmhv25fJbpNobaib7/zIQd92ksGYjnOYCQ37wiNNaYhwLBE0K5DpxefQpXKbQIwVB6ArdJMFl3CW5itWuCzDry55INLQOgLMicFrOQmthFgyT8aBEg== 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=R+i24iGZ9RERTlxyYIlSl1yFli7Tg6Dt/zc+h9CLCy4=; b=RT9g0UBGUKU+F/N07WrlQVR7s9Ly8vHWXNX1KQPx88OlUZjTJbDzcOsPcurWubLE9x4gjZlgelYGOoBBTAdU1Ipnv3roSm00+N0EOE1kbiZmETQNFwmRuYo7bhhIMN31abAEElICUn2LndDV9hApROP2HF94LmKWyluk9itq7LCLJXFwx5P/7fgfUnkUZznMZGLlIWgsWy6qfJLf7S2yolIJ7iDB3lJRCx0zsH7WdSWV2Ah2jf53ZP2XAJMluuBVN/R2BzJyntWvk1RZAIiJ2tdcQl8rlGXuQPzuBLmH2ZOod0LLv+uwUDq+xQJ9PqFGTHOqqJXSBIkJW2SQkige1g== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=R+i24iGZ9RERTlxyYIlSl1yFli7Tg6Dt/zc+h9CLCy4=; b=ORkqSgK+28NDKTr9N7PZTm6yT280PKMAbCNYBI2KO+aVobirfiYBf0lwmTrd2nxKOdBbRzYAlV3gc93Zbo9bm9fThbwVmz9/4mX4yt9iCwyD2TLbTE/wHR+Xp/ND1pj5crNWwPdk6IWmheY/O88nQsuQLyCR9LLNWUHb+kOjgkE= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=citrix.com; Date: Thu, 16 Oct 2025 12:05:15 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Oleksii Kurochko Subject: Re: [PATCH for-4.21 00/10] x86/HPET: broadcast IRQ and other improvements Message-ID: References: <8d94abf8-70d1-478c-885e-ff9a960ac72d@suse.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <8d94abf8-70d1-478c-885e-ff9a960ac72d@suse.com> X-ClientProxiedBy: PR1P264CA0086.FRAP264.PROD.OUTLOOK.COM (2603:10a6:102:345::12) To DM6PR03MB5227.namprd03.prod.outlook.com (2603:10b6:5:247::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR03MB5227:EE_|DM6PR03MB5161:EE_ X-MS-Office365-Filtering-Correlation-Id: 39dbd9ef-2326-45e1-3a1f-08de0c9b833a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?N2VJUER4ZkRZK0IxM2lrR0o4akRxS0pUazhpc2ltN1pGc05iTFZ3MkxNMnNH?= =?utf-8?B?eS9LZnJnOFA3VVpFSlpqUjhWUG5mcFk0R1dnU29LWmJKN2E3b3hVcHdlQms1?= =?utf-8?B?M0VuYnkrTVBKZTdyN3ZCTE9GREVaY0djcWRnWGdpaXVmMWhxUGt5VWh3WHBO?= =?utf-8?B?L2JiVkM2OVFJQW55cmNIODhRKzlPWmlVMzhMNUw0dlY2ajF4L1Azc2FGM3FM?= =?utf-8?B?b2xMaDhtUVhEdkxVeldKMmk4MTJvQ1hzQUNpUENNdUlCNVpKNUY0aUR1c25G?= =?utf-8?B?ZDJVNXN1UWM1RFV0cWExcnhWemN6UXdQb0RNQWJnN1BTSUpGK1kvMHVhTllI?= =?utf-8?B?UldmMVo0U1hUVituQUsxdEwrNWM4NUF1ZVMrZXEzSVd4UnZOT2ZVZ0ZraXdO?= =?utf-8?B?MTZxb0taMDdqUnN4Nm5kL2FvQ1lmN0xOUktnNUsxVngxUUFvVWZBQXFZaDA0?= =?utf-8?B?cE1BcDNhYXBGaGVhN3dkdGxJUENUdFdlSXh5VHBKZlhFbVBROUtqVk1ua05v?= =?utf-8?B?dHdUemhtUERZTStMQjk5NVE2OXF4S3JlL1ltc0dqYzc3ME1XK21CWi84TW5n?= =?utf-8?B?c1FRUXZFWDNRd0YzMGtCTXZPZDVDRnVyRElKaUV4SDhhdjU3UytKakZGR1pU?= =?utf-8?B?Nng3aUcyZmlQRHQySGdOdGNCODdYSlJpemZhNHVxOTVUL082ZkRqb3ozTGhV?= =?utf-8?B?YkQ2bWgzRTQ1RDNndzkra0RhVEtsOTV1ejh2L1gvVjFVZkI0Z3lrakMvMjds?= =?utf-8?B?dWxNb1dKWi82MGZpUDI4VERkVFhDQlVRZHV5SmJWMU9PRTBDc2JmZW1nWk5N?= =?utf-8?B?R2ZjSUJzbEpRSWdhZW83cXRRV2ZBSHFhVlRhaERvU1ZSRjdSK05xRjMxZ1JS?= =?utf-8?B?N1U4cEUvcGNtNHZLTzNiVkVmOXpnanU2dVBhWFROM1VocXpkY1Zjanh1R2tB?= =?utf-8?B?RUFSSE5GdE9wc0tUNHl3d0piV2hZaDRSY2RydlBPbnhYTlYwaGRKT2F2bVVT?= =?utf-8?B?cmg3MzNVblpVaU9tZnJ6S0NNOFRNREE2YU9Fb0Q4TG1PRU1OY2JtaWFmKzFC?= =?utf-8?B?Mm1xSDlKL3VZTTB0OVNBTDRPdmMySy9wWFNoY0IwY0JpeVlNSXZRYTFKUWkw?= =?utf-8?B?ckRUOHJlTmpiWGJmNHRrRU1TcWpiRDJKdkhNT0sybDBUMzdvQmJMUUY4UVE3?= =?utf-8?B?cWt6Nms0cnErcnZ1c0JhTDEvYm1HL05qR1RVSHc1enVhUFhicDJhc1BZNWRL?= =?utf-8?B?d1p5MzEvK0IzZjhqN3BYWTBobnorcHJITWszL2pLdndBSlBYTEdaSE5KU0o4?= =?utf-8?B?RDNORXBWbkJHRUJ4UGR2MUFSaThrSVBBbTZzcXBKVGh2Y2M1SjNqNXlSRXJO?= =?utf-8?B?YVYwbk5GZzZybm5zRmo5YWNJUGJ4djlGVDBaKzFudldObEtHSTBTSFI2YVpE?= =?utf-8?B?NldjZHNzKzdIZFQ5MmQ2VVhUZXlZdVk3NkpnbFhENS9INFJVZXAvWHhDL2Jr?= =?utf-8?B?eW9DMXZFU2xhNlUvdlhETVZBdS9RcGlxdldhbGxHazRXb2RrdklxR2J0Y3FE?= =?utf-8?B?ZFhvY05GcE1JZVV6MXgzK3RCWE1lbjM3c0pBTUxWNUJJTmhHSDJGNnVXbUFN?= =?utf-8?B?RVEzemk3d09ZOHNXdlVpWjhrU2JTS3R1UHE2YjdNQmlpMllNZTB2WHNURmJr?= =?utf-8?B?QTJ1Mm0yeUN6T3lQWmpocGVaT2tpM2ZXOVFXUjlGbE1NUXlaY2Z5eTdZeCtJ?= =?utf-8?B?RDJOWXZ3b2VRbkJYTk1ud0RDaWQwRnFvQkJ4ZUp6QzE4NG9hWXUyK0F2cEFT?= =?utf-8?B?VGtSMTUzdTlQWkE0VE1hNFVlbTNTaldYV2lMa0E1bVBpbTkvRkpxMW11RW00?= =?utf-8?B?Y24zYmNIQzNINEpTM3hzR0lVQTNFbEhydjVqRmVreDlZbzRwMElsZXZHa2F5?= =?utf-8?Q?RQL0hz6zbhzWzSFBp3stFzKqVzrsMCgT?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM6PR03MB5227.namprd03.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(1800799024)(376014);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?Y2V5dC9selhsLzEzT2FSNExnTUhjRUNzMzhEZFk2NEtUTndxdmoxQ0NVcjEv?= =?utf-8?B?bzdiNmRTVHJCNW16UWZOcEVxTHp1NFloZmlNc2lqTmhHcDI0dzZ4SXFGc3d2?= =?utf-8?B?VmZSekhRUWJKZUloRk9Xc08zWDVxeTN2YWZMcG9lWWZvc3RmTlRFTHB0SVQw?= =?utf-8?B?T2E5UVhlcXpPbGsvSWlUdFRwaG0yRW9JZ0JRQkk5NmVuek93U0hCT0IyTzFi?= =?utf-8?B?WW9oeUpoc29wdUlXZ1g4d3M1dEJEUmlYYU9va3gxUVV5R0l2WWRhbVFZUnJp?= =?utf-8?B?L0N4T1ZkKytCb2dRT1lja0FNZWNINEJmUXpBdndyek1CZFJSa2kydjZKL2gy?= =?utf-8?B?MmM3V25LSjl2bG1ZbGJlNmpNU0prbldDVTUrQXNTUXduNWFFZm5nY091RjIz?= =?utf-8?B?N3FJUUpGNVVlSXJ0TGJTV0RLSjZpVXo2MnZ4S3VTT01IbWhWcTM1eFVtNTdt?= =?utf-8?B?SlZ4Sk9nVWtPa000di9XTTJaMDVyNSs1czNhSWdEakgzYlJxQW9vUUNsdGNj?= =?utf-8?B?Q3NoUXlLUnpraXBiUFNCWnBsUFJRS2dabE54bEcxOWJ3ay9DL0xLV0RLZlQ0?= =?utf-8?B?bEJTajhackhNN254VERtM2dYVC9EazJJbWJEYmI4UUVDRDFaN090RDFhMURN?= =?utf-8?B?Qk9nYkxyd2lWK3lpL29ZMEhxeG0xSGJzdzQwQkNOZ1RiRU1iSzF4NDR5cXhN?= =?utf-8?B?MW8xUzhkbXFCV1BlYVdVK09iSFBUZExVSUdPRW5kTmpuK3RNeG9BNHk2RXlk?= =?utf-8?B?eUFmMEozc3pRcDZJb0daV0Fyd3FFVnVFaGk1V0ZnMStKWjdVandQSGFjVENk?= =?utf-8?B?bXR3N3BDeEhoRlpZZnFMSThwRmd6SHloeDF4b2NwTVh4RHg2R3lKOEZYYzZ4?= =?utf-8?B?VnZ5UTg0RElUK24xSldmanFGbzc0N0tEcHVJYi9NR1huNktZMmVrZVg5bXJa?= =?utf-8?B?VlVmWFFDUjAwR3Z5YnlRZ3pLc0ZIZ21KLzZKcFUxUnZOaU51TGpWUkltTmJX?= =?utf-8?B?ZHExL2FremVhME5iVnV5dHE4MDZIM2x2Y3dBeFJnYXkrM0EydEtpa0FFbHlU?= =?utf-8?B?dW5VLzJkNURsNHIxeGFUb2tqNURRQ3hsZ3pqc29TS21xcUFuUFVQOGw3WUdp?= =?utf-8?B?WFVsTWFsZXNlanBZTVJRV3hJNnhxWGluTGVtTGxMcW1VaDhtK0x4UUJUSlNS?= =?utf-8?B?MGtRbDhLSTlFei82RWY5bklHUUQyakpPQnRWNHFGUzBad3lJeFk5SDdNMDd2?= =?utf-8?B?UE5IbUYzMGJUMlpmUkZuK1JuY1RwK1FraEVOb0xrQ0pzd3VNbStmV3Y0SzZW?= =?utf-8?B?NHZ5eUQ3RnI2cFV4L3NkajZjUTJhaHpZVTdDUXg4Y1VEelB0TXFTZnNoSHAr?= =?utf-8?B?VkVMdWtCbkxVaXpjYmp0QnVtNXpwdnVra1lSeTV1MlBWTUZjSm1oa0xwaXR1?= =?utf-8?B?NkVJNzdNblNqZ2Q5aFFqMFFVaGF1K1Nxb0NsY0EvVkpUSzFuM3pCS2F3Ymta?= =?utf-8?B?QUtIdXlSUWRFOWRIUGI1VWdOeHIvNzExTXNLOWZBVVBId3BldmtFb1h6bGlX?= =?utf-8?B?SmVVOEkxT25LQW14YUR0R1RoVlZBVC9yV3phaG5mN2I3c1B4VFJVMGJRVXVN?= =?utf-8?B?V2VpVWVqaTNQUlZ1TGpxZWs2QjJlNXZnMzhHSk5kVHR1STQ4d0tTV2lENU5V?= =?utf-8?B?T2wvL3FRN0p1RUEvaUNETERZUDY5M0prNjFFSjBHT3Z0dmgzNW5SL280V0Er?= =?utf-8?B?VGVuMEdqWEJ1Qm9NSXFMNUQ4RW95OGx6cUtjZHE3WW5ZRi9tTmcwZmRmUUoz?= =?utf-8?B?SGw2Q00zVUI5VkwrZ0Y3WkJBYXF0ZGV6enFVTW94UkEvMTBNL1IwVVR5UFBM?= =?utf-8?B?RVVoZkZoamN4cndJNGxvNnBCSlRtaEdqUk10ZTFhQThoa1YxREo1S0ZLUnVz?= =?utf-8?B?d09ZOVRONUpkMTQxRjM1WVpnNFZIVGhscTgzelQ0QXdmamtOdjdHOTJFb3dJ?= =?utf-8?B?b0p2RGxKOWp1NUdtWUsxYVFWS1lYTnp3N1FvN05aVEpkTFZxb2tXSFNhWW04?= =?utf-8?B?T0hlcjB5c0lXTStSbWRMQjNQa2lObmFMVHFFaEU1S2Z4d2pBTDNXMi81L2F5?= =?utf-8?Q?pZOmh4hUCAuCrVc/1vnUan47u?= X-OriginatorOrg: citrix.com X-MS-Exchange-CrossTenant-Network-Message-Id: 39dbd9ef-2326-45e1-3a1f-08de0c9b833a X-MS-Exchange-CrossTenant-AuthSource: DM6PR03MB5227.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Oct 2025 10:05:20.2536 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 335836de-42ef-43a2-b145-348c2ee9ca5b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 6Fva+86pbU6PBw39hXu8yDQdjwS3MAKGF5MyChfKB854usCWjGSej4EbCGI5wh4M72n7jvDkaPXMREhGhFFFmA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR03MB5161 On Thu, Oct 16, 2025 at 09:30:28AM +0200, Jan Beulich wrote: > While 1db7829e5657 ("x86/hpet: do local APIC EOI after interrupt processing") > helped quite a bit, nested interrupts could still occur. First and foremost > as a result from IRQ migration (where we don't have any control over the > vectors chosen). Hence besides reducing the number of IRQs that can be raised > (first two patches) and possibly the number of invocations of > handle_hpet_broadcast() from the IRQ handler (optional patch 4), the main > goal here is to eliminate the potential for nested IRQs (patch 3). These > patches are imo 4.21 candidates (with patch 4 being questionable altogether; > see there). Patches 5 and onwards likely aren't important enough anymore at > this point of the release cycle, even if those with a Fixes: tag would likely > end up being backported later on. > > The one related thing I haven't been able to find a viable solution for is > the elimination of the cpumask_t local variable in handle_hpet_broadcast(). > That'll get in the way of possible future increases of the NR_CPUS upper > bound: Much like right now a single level of nesting is already too much, > if the limit was doubled even a single IRQ would end up consuming too much > stack space (together with cpumask_raise_softirq() also having such a > variable). Yet further doubling would not allow any such stack variables > anymore. If there's no nesting anymore, you could introduce a per-CPU cpumask_t to use in the context of handle_hpet_broadcast()? Thanks, Roger.