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 D9AECC44500 for ; Thu, 22 Jan 2026 08:50:35 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.1210512.1522159 (Exim 4.92) (envelope-from ) id 1viqOO-0006sP-1d; Thu, 22 Jan 2026 08:50:16 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 1210512.1522159; Thu, 22 Jan 2026 08:50:16 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1viqON-0006sI-UE; Thu, 22 Jan 2026 08:50:15 +0000 Received: by outflank-mailman (input) for mailman id 1210512; Thu, 22 Jan 2026 08:50:15 +0000 Received: from se1-gles-sth1-in.inumbo.com ([159.253.27.254] helo=se1-gles-sth1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1viqON-0006sB-FC for xen-devel@lists.xenproject.org; Thu, 22 Jan 2026 08:50:15 +0000 Received: from DM5PR21CU001.outbound.protection.outlook.com (mail-centralusazlp170110009.outbound.protection.outlook.com [2a01:111:f403:c111::9]) by se1-gles-sth1.inumbo.com (Halon) with ESMTPS id 5d77eade-f76f-11f0-b15e-2bf370ae4941; Thu, 22 Jan 2026 09:50:14 +0100 (CET) Received: from CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) by BLAPR03MB5652.namprd03.prod.outlook.com (2603:10b6:208:296::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9542.9; Thu, 22 Jan 2026 08:50:09 +0000 Received: from CH7PR03MB7860.namprd03.prod.outlook.com ([fe80::f5ba:35df:1c9f:b343]) by CH7PR03MB7860.namprd03.prod.outlook.com ([fe80::f5ba:35df:1c9f:b343%4]) with mapi id 15.20.9542.008; Thu, 22 Jan 2026 08:50:08 +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: 5d77eade-f76f-11f0-b15e-2bf370ae4941 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=DPy7EP3B2M9VsSUa0/L5/2J0hQeWLjb6qdaUlYlz78lBACO1gIQlqsweMmN7cs/zuKqNpTdca+U67Dq5O2YVBa+YJN9PJ+N6wL9oXTpphB8UiDqh4vlo39qHgsPKGqYZKs7u47wTSEInJFja17jwL6Q7WKOU+0h3j7cwW4SoWhQgnTr+T4eWxTAKI3u5G6scrWHbRDjVbUsPPM1FUXoguRmELg9GMBR0Efo+K8RtptQ1r7JF5n6KMdnk7GW/MgEw8rw6tD7HktdeC+12YYsfmLuPV2DwgUlQqM+u8vn95VquouLDB42hGcRyNrLx8rPydjEkEICUdCIhGuYr16yK+A== 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=q3iOoc/nuBc5WkLGONORTWrb2TgKuY7zFb0BolB3EXs=; b=XifPg48VbS+/QGBnFQ3+9WAuIibUUHcwYjfd618kkZdeM+7D9mLeZAK1yKqw7iJSVXzo9An2iC1JpMqVEae/ZzHSdfKnvR7HoW+HVwRJHFrgwmdXF82baxyuqcNTdgD3y0VqOMrmIJ3rpLg0wji/d2fW/YRnUzLeJsYzy9O5cUNQ9PmD+JsqoVCEziBRc2KK0MLtiRtR1QdfY7mtca4rO8N62wPfYuIF1I7UiWCdPBR7zLShxjGy+3c1qL4kxWkm1J5hmST6eoNiTdrBlKcJljBO4ZAZ/09t8G7f6kdhvX8J096IBJAndoYc5/VCB1ID8eGk8+utQCmVTRnHsaxVjg== 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=q3iOoc/nuBc5WkLGONORTWrb2TgKuY7zFb0BolB3EXs=; b=qeYqqPhUsJOLhL14hh4UClLQbe4o+WsG26pwoLpq3zDCYWXyskgbwGXDsSxZofmoX9PUbdnJu5KBvnOnADRGbuLSyNM/iFaD1i5a/VHSAh75iVeEpUPxVV/WmpqiBOXJ1JIOE15d+B2biS3OnEKyNrbCmWtX3CjMDrMqzoTeU98= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=citrix.com; Date: Thu, 22 Jan 2026 09:50:05 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper Subject: Re: [PATCH v4 3/8] x86/HPET: move legacy tick IRQ count adjustment Message-ID: References: <57f34114-54b7-483d-8ac0-e9fa49df959f@suse.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: MA3P292CA0013.ESPP292.PROD.OUTLOOK.COM (2603:10a6:250:2c::6) To CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH7PR03MB7860:EE_|BLAPR03MB5652:EE_ X-MS-Office365-Filtering-Correlation-Id: bf196b5d-be88-4717-5df4-08de59933f17 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|7053199007; X-Microsoft-Antispam-Message-Info: =?utf-8?B?ZjVtUFNtS2hUVjVNWkdSVEhKWkw3d1lBU0dZd2lYL0RwUDM5YWZmc2UwNFM4?= =?utf-8?B?YnB1aVYvWXJrMnlrdFU3VU1SVG5sY3B6MWh1d2svZjJMalN3QUpMeVYrK0w2?= =?utf-8?B?Z1J0MEFBbnZhQnduRE1Hdnh4cnNWNmdPTDhCOHNTcm1WQTRvU0gvTlFaZTYw?= =?utf-8?B?bU4wbUZSMG5xc0ZraW5Ob0toRCtZeEdzSVRXM1ROVGQvTWpkT3JVVzJlQTVB?= =?utf-8?B?V0ZieVZ6SllRdjlXNk1XVk9QMFVQQUhxb2JsZEt2THA1cUpTSzFVNUo2QW02?= =?utf-8?B?akJ1eTNtOFFXQlVnOVQwdlRmRXhYZTI1UUo1azJJQjNjV2g4djFRa2t6Ums4?= =?utf-8?B?NVN3NFFMeFczbE5VbkQvRGg4V0s4NWdsL2ZjblA5djBCSTBFVjhob2M3UWRx?= =?utf-8?B?STlMTGZnbm9UZmVJVU1oem5CQTJSU3NEVzJzd3NPcHJ0RFI2ZWZJMS9ETFlV?= =?utf-8?B?RVdaS2MxajBURzY4ekhwYXRjR3o5VzJYVzdsZ0pXd2FweHNmRGhUeTVqRnlW?= =?utf-8?B?bDdYb0ZDblB2Z1VlREZrQnBjOGwxeCt1L0xaRFRxdGxRQWJBdEJjSTBuQWdR?= =?utf-8?B?bnJ1T0JWNzN1Njd6RmZzZ0FvbVRpV21KVVdTcFJHSmhYODJkUFhkQ3pHbldO?= =?utf-8?B?Q1RXdHBnSjZwRjhTWGh2aldyT1ZwQndnQWNNYWVFMTRmSjhVbmhRcy9ZbDVU?= =?utf-8?B?TTJHbmNOdHhLMlBnVW4xQVBibkZ3MUNINlBrMnNVY1E2M1NHVEtmNEVRYSs3?= =?utf-8?B?U1dZamVDaGtOTlJGUm9zRGJpRHVRQlRCMVRJK0Z1T0d5ZWdjVW0rV3U4bTR4?= =?utf-8?B?OWVJcGFoUXdqN1RJSGlnVEdWekN0RVIyUHJQYjV3R2hCM0pIYWJpVzl6UWV5?= =?utf-8?B?Vm9FVTgyWDFYZVZiNGhISkJvbTRFVWtSaERhZ01BYU5VdDVNaXJiSHBoaDZy?= =?utf-8?B?Vmg1Tk5JOXJFTkY1Sll1czBlaDFrRVY5OGhoaE9qTzhSVGxrbU5USGd1MUF5?= =?utf-8?B?T3gvQmJXS2VMYUFZOVZBWVFmSStFKzVzRGpTOHAzd0dXNGV6WGh5czkrd04x?= =?utf-8?B?MHM4TDZMc2QybzBTK3RnaDZDbjZiZ3h1U1VVYkRlWUl6Q2JXSHJMemJYNHF0?= =?utf-8?B?U3RLenlFelBONkMzcVBQUTNMeHliUHZBbUpJNTJmNUVuSjlhMnNWclYwWGlY?= =?utf-8?B?Um1hSHV3MDNTYkxrUGdwSjd0V252VjdRTFcxUUFselZac3FJaUFoZExhY08z?= =?utf-8?B?c21SMEZLTktRcWtSWXBwdjhsKzNmcXVocE9JVGF3R1JMVGZmaGxpR1pEd2E1?= =?utf-8?B?WmJDYk51MWdiK2cvK0VVcllWZE5xVnZmQmY1eEtNMVVJWk5tS2g1SVVSc21O?= =?utf-8?B?dGtsak02SzlmNy9zK0N2STVuZi80VDlvV1AzM3E1YkRrdmw1aTh2dDlwRGdK?= =?utf-8?B?bTh4RlQ1NnlaUTZ0VUViTUxWRUMxbjdMNVpScXVUTW5kYTltWnNRcGVPelVv?= =?utf-8?B?bUROOXFCZ2M5SFNib0JqMldlVndBaWpCS2Z2Zlorc0tkOUdvUXdDSEh3N1Jj?= =?utf-8?B?Mi9FRDhiV3UyMmtnSklOR3VESkVsMklrQ0JtRXRyYmtkTnhmSkxYVUQrUjAw?= =?utf-8?B?Tm9tQmt5QnFwWk9yMmNzMWdwUnJ6cThmT3lJeTI0ci96Lzkrak1kWVM0SkRy?= =?utf-8?B?SHRtUkVaYWRUQWdwRVIyUnArNVlLc0J1WERyd0NnNEN4ZGNPa083ZTlwa21m?= =?utf-8?B?ZHo5T0hiTFA1V3hNL0FUeUlKZDBqT2RIVEN6Sk1jb2RpY1h6eDZ4NVVyS1NN?= =?utf-8?B?cVAvT2o2VmM5ZDk1N0RZa0lvNldseVlWZkxlNHRlZDZRM0dlMFI1cHkxeXlL?= =?utf-8?B?UG1kN09LRUpMMW0xczk2ejEvVlMrMHpPTHB4QSt5TkRxWFFpdmZ3QUMxbU9r?= =?utf-8?B?VmlGdStYeG9IVGdmaW9TOXAxTzR4ajF3R0R4WnNnYUFDMWxpMGxqRjZiSzRy?= =?utf-8?B?RjNBbGhGSlFhZG9jZjAyMytQcXZDYTFoUk0xVWJQdkJuTFVpLzJBb3lGR1lQ?= =?utf-8?B?VU9NSU55Qk1NWkI4bDdBcEVXTlh5a3JZWklNbFhlaWJ0VWJueU1DbnpyQWJ0?= =?utf-8?Q?lpgs=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH7PR03MB7860.namprd03.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(1800799024)(376014)(7053199007);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?ZjFvdnQwMW5yZnhlQldzZC9MK1lQZXVDeGVOM1h4YnpqenhWODU3bFd6Q0hY?= =?utf-8?B?UHlnUnRZdzBneWhsdlEvemxueGNiR2FXMWRwSGpPNHJhRXRSU0puSDhPSWlE?= =?utf-8?B?SUNtQ0FsOXVJSm05Zis1ZHNzNXE3Z21tZUxPRlAvSld0SzkxU2g1M0lMbVFl?= =?utf-8?B?RWIwWmsvVTBnK0dqWmFnUXRhS256czNSaHZMejl2MjZkanZSRnc0WjdvQlFZ?= =?utf-8?B?SUZJL0xKeVJiUy80VGcwdUFHeEc1WlplMW16WW5naWc5NUNsMWhXQW45RWNp?= =?utf-8?B?azEzRHFWM2VncTl0REI1L2pvVFV5T1BGdWZVRUF2L3VJMjZMRlZzeEJ0bC9X?= =?utf-8?B?NGR1RzVibzlRR3NXZnZSckdjYXRPdUZNa3M1YnJJQStEZ1VleFhIa3l0Qk92?= =?utf-8?B?cjIxRFc1b0hjNUZ5VTY2Z2J6UkRNVHBSTldsZFhqcTY1RTNObXZuVDRwUHVx?= =?utf-8?B?UVFCK0dRbjFqQnNiWmpzV1BvNCtOQWJJOWtXc3U4cGpWbkdHclp4REU2NmVJ?= =?utf-8?B?eDR4dTQ2bTFQQlNucVV6WllvTVVDTXFuQklsSTQrODJkMWcrOENkQ2F1Zjc2?= =?utf-8?B?dm11RUhUMUlNRDM3YnRxdk52TGNkM1FaVEJ6dUdsNjM0c2hLalNFdmNVT3NI?= =?utf-8?B?bkQzbVRwTHpOanh3cmhZNjdsU0N3Z0ZiSEJaVXN6NlhBWDFjRDlLOU44NGhu?= =?utf-8?B?bXAwdmZMY2NraTJYaUk1TmFhZGxXb2gwRitwQis4Qy9LRDZNekx0ZEhmdS9z?= =?utf-8?B?VlRtSEt4SSthZ25Wa09jYXdNRnc1cmU5MEUrK3RrYWt1Zm9lNWlvRGxKcnpI?= =?utf-8?B?TGliRjVzcFAweHFSMmpDeGQ2OCtGTE00aEk2VzI5MFFVa2g5UTM3TXhXNVNx?= =?utf-8?B?OVYxN0F1YTRob1Bsb3RDVG1qL21RQVR4MFlYWlg3VkJVY0t3NkFHbHV6ZDYz?= =?utf-8?B?Z0NaRUZZUWJUd0VqdElRM0M5Ny9Hc2FqYWg5RTNVR25aOTdSTjBsZXF5RUtJ?= =?utf-8?B?dHRkWW9yQldMcTA5OW5TZFZmWWlCQnhEU0NLdHVmMVNLajhRYVdqZ0YvTzRs?= =?utf-8?B?WW1IZllxaVNpRGs0eUY3MnBvcHA3NndaRkE5QlYzMk91MitlTHk5dis0T25m?= =?utf-8?B?NFNpcURJaXFoL0xMN05HYU9jWXdLVGs1MTRNLzV6ejBoKzFEN3Z2ZlcxSFJV?= =?utf-8?B?WnN1ZE0za2cxMURJZGcrOGxhZDR1SlNvMHJDcU1lbW9keE1Gci9kcEg4WVVB?= =?utf-8?B?RzI3UjJrZ2NQWkQ0UlhVOHNLVWJLUXIvMEs5NGlXUVdDTEwvdzJkY2xrb2J4?= =?utf-8?B?Kzg5OUpHWm45eURUVjM3UStnV1huQmxOQ0w4Q2ZmbnNzai9zL3JSNy9SSUtl?= =?utf-8?B?VjdnVVRwYzRtR0RoOUMycFFtY29iOTFJb254TTMvZVRQejBFcDhYVDJLOVVy?= =?utf-8?B?UnNjL2R0TGVlcklHdXBXTVNqMVV1L0RScHljNHdOMGpRckprUVFKcGpoVE9K?= =?utf-8?B?d3N6cjhhL0FhbHVFR0J6cnpaaGJUYW5LNytCZzdxVkg4M3IxQ24yRmdsbGJB?= =?utf-8?B?VW4xUEE0VjhhelI5WmZzNHFNZmt6ZnZnWFhScjcxalhHYkFWNkl4bGg4dmdQ?= =?utf-8?B?cXdMNzlFSlg4d3UwWVZDN3plcnN4RkpHdG5vSU5CbUpOZm0wNzAvK2pzUEJZ?= =?utf-8?B?RXFSVEo1UGlFVnI4SjI0TjB2T1ZCRGZtSnhVdUYwWUdEYjhCRWUzNEJBaTdF?= =?utf-8?B?LzExamJCTS9tcTU0Z056djdNdW5CUEF5b0IvRjROUTQyUUZuRHgwdGJNZkJp?= =?utf-8?B?ZytBK0ZmZDZIb0lNck9EL3lDbzkrY1lmM2xkb0d3TlZsTEI5QXRiakVCZlVP?= =?utf-8?B?TEZrOE1OM2tmbkRjR2FyaFpvOUhyVms2MHZqNlU3TmJpN3doSjN5YUYxNFRL?= =?utf-8?B?Znp5SVNUelVBMG5qc3Z5eDZxb2dEUnlPa0V0WlcrbnczUUhqR2tiSGxIRzNH?= =?utf-8?B?a2gyV1Q4UjFDMUo0OGhIWjBwcDhEU0Z5RDM0Z1lsWlV6cWg0WHBsQUJYbzBv?= =?utf-8?B?aEhTSm1SVlJCMGJodDZLRC93bCt1cGp1ais1c1RKTmpDL3BxbGZCSkJBN3JU?= =?utf-8?B?Yk9ERzZsSEZNbkJXYlhWZ2c0cFg3cVpYV2VLT3BxRkEyT2FJdVNOL0N5S1JL?= =?utf-8?B?b0hjWWxCbG8zb3pyYmpFM1J0QmhGNmh3VE53TDlqVDJoVyszNUM0ek5ZSGRE?= =?utf-8?B?alFCaStqUktsMzJwQWsyNy8rVUU4ckZ6MTltYlZVMWtiTFl3TE0yaFZJcGRz?= =?utf-8?B?RWdEVk5XRk16aXN3ay9Lalp4MGdJNU9SaWRHSW1QT2JrV1lnVVlRQT09?= X-OriginatorOrg: citrix.com X-MS-Exchange-CrossTenant-Network-Message-Id: bf196b5d-be88-4717-5df4-08de59933f17 X-MS-Exchange-CrossTenant-AuthSource: CH7PR03MB7860.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Jan 2026 08:50:08.9024 (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: ggz3vXJcdLSpXsD2c/+FWCyZZqK3CVpQsE0B7kqK5HUKkn1qPaf3YZVZ8KOI+XT70dD433PsdUsWp4DbP3nUIQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BLAPR03MB5652 On Mon, Nov 17, 2025 at 03:37:45PM +0100, Jan Beulich wrote: > If already we play with the IRQ count, we should do so only if we actually > "consume" the interrupt; normal timer IRQs should not have any adjustment > done. > > Fixes: 353533232730 ("cpuidle: fix the menu governor to enhance IO performance") > Signed-off-by: Jan Beulich > --- > _Why_ we do these adjustments (also elsewhere) I don't really know. I think I have an idea of what's going on here. This accounting is used by the idle governor to decide when to go idle. On Linux (where the code is imported from) the governor took into account the inflight IO request state. However that's not available to Xen and instead they decided to mimic the tracking of the IO activity by counting interrupts. I bet then realized the timer interrupt would "skew" those results and make it look like there's IO activity when the system is otherwise mostly idle. > > --- a/xen/arch/x86/hpet.c > +++ b/xen/arch/x86/hpet.c > @@ -808,13 +808,13 @@ int hpet_broadcast_is_available(void) > > int hpet_legacy_irq_tick(void) > { > - this_cpu(irq_count)--; I think you want to pull this decrease into timer_interrupt() itself, so it does the decrease unconditionally of whether the interrupt is a legacy HPET one or from the PIT? By gating the decrease on the interrupt having been originated from the HPET you completely avoid the decrease in the PIT case AFAICT. > - > if ( !hpet_events || > (hpet_events->flags & (HPET_EVT_DISABLE|HPET_EVT_LEGACY)) != > HPET_EVT_LEGACY ) > return 0; > > + this_cpu(irq_count)--; Also in hpet_interrupt_handler() we might consider only doing the decrease after we ensure it's not a spurious interrupt? We don't seem to decrease irq_count for spurious interrupts elsewhere. Thanks, Roger.