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 EA6B6C61DA4 for ; Thu, 9 Mar 2023 11:50:43 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.508239.782708 (Exim 4.92) (envelope-from ) id 1paEmx-0003Ar-Ek; Thu, 09 Mar 2023 11:50:27 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 508239.782708; Thu, 09 Mar 2023 11:50:27 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1paEmx-0003Ak-Bc; Thu, 09 Mar 2023 11:50:27 +0000 Received: by outflank-mailman (input) for mailman id 508239; Thu, 09 Mar 2023 11:50:27 +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 1paEmw-0003Ae-RP for xen-devel@lists.xenproject.org; Thu, 09 Mar 2023 11:50:26 +0000 Received: from EUR05-VI1-obe.outbound.protection.outlook.com (mail-vi1eur05on20615.outbound.protection.outlook.com [2a01:111:f400:7d00::615]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 93d304d3-be70-11ed-956e-85ef70e17bfa; Thu, 09 Mar 2023 12:50:24 +0100 (CET) Received: from VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) by PAXPR04MB9232.eurprd04.prod.outlook.com (2603:10a6:102:2ba::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6178.18; Thu, 9 Mar 2023 11:50:21 +0000 Received: from VE1PR04MB6560.eurprd04.prod.outlook.com ([fe80::154e:166d:ec25:531b]) by VE1PR04MB6560.eurprd04.prod.outlook.com ([fe80::154e:166d:ec25:531b%5]) with mapi id 15.20.6178.019; Thu, 9 Mar 2023 11:50:20 +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: 93d304d3-be70-11ed-956e-85ef70e17bfa ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=gDYE8aS0BMC06tygulo8EYwI5jZZUS1ne1dDIowKXAGfhnDCpO+78wRv38YnyPsQDsWgf/g9Rr1ZRMj0eDz86rR5Xva0oSHrydwYEaKjREs4JAfqczmGz1xbqxJNLeq1wy4Peu7HkSpI93I83CxnT1hoZx30KodOf9tlyV6jSiHB09fMbgeu7YCKSa0yct00j/TmvQnFERWp0CGP7dsz97vlpbiPppHNF1olXdl6oVjW99JkOnytD27/luAjj14P+s4BSlXVFdouddXzK1gq45WMRDXu64Wxz/+s+voQr6ZavIobMfOJDJpc+EBpXoobvxQUF1YbBXcsORVeyUIl9w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; 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=AhTy63ilfnHNvv7Js3SFg4IEG5X6YAWJTFYXUhxEUVM=; b=IWKTE5HwwlBZJzgmfn9dABwPZvQOlBQGX9bZaDIyF+zoRueLIzsf50gMjc8ojH/ypUsMcfcp8PBJYdjEIzDk5UBM7lPWZZu7CnjS0zH8tj/Mnw5le5AWwWgJ1eVvE1Cx5oThkDBSqzjXmbo3oueCJnTGU8aI3+N2gcA61wnhahTNpwI+iP7+fXpU2bEmAYaLut0FamVJwaeeZbgrVWbkCF0ffQzccUAN+qzWMbi2LUuM+Y6z5x0M3xgkX+tfvgcdh/CuRYNYPMefnOJgtl7kKykc/37T9nyyDkhCXl7kG6aqeFDv+/hJvFnOssfDnOYlvjkB7QlFxPPlx4WMx/K84Q== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=suse.com; dmarc=pass action=none header.from=suse.com; dkim=pass header.d=suse.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=AhTy63ilfnHNvv7Js3SFg4IEG5X6YAWJTFYXUhxEUVM=; b=RUGlZygNWSHvNt8Lmi5NQLRM8rWTRYkWi0nUX843EaikKNIIPX+eX8wX8BPUlAmi4zwMuNv/LdURwNxxP7RfIR/j5EGqW0fZdGDmaG0GlCQ0RumDWc4o7XAbCUpGB89v5MRKsMMA0QU6O3h6J/M4G3ss2jum2zTs1XYU43chLCveTL1XKn2LnBuK8zx9aJvYFHl96AWQNSF8gsKobmpovoOnLMz6YgotVYwvvDKp7n1ahkRbFIk8xqZW/jObLuT7mYpDT4VKA9WflW29S9UqA96RacKubcRGwANFFuneSvMBHcDGT66AZep7WcllepZaFgE24t+NuARyPxqPfF1IhQ== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=suse.com; Message-ID: <645fcd9a-755a-e2a2-f332-93c5e571b9e5@suse.com> Date: Thu, 9 Mar 2023 12:50:18 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: API/ABIs: Re: [RFC PATCH v2 0/2] Add a new acquire resource to query vcpu statistics Content-Language: en-US To: Matias Ezequiel Vara Larsen Cc: xen-devel@lists.xenproject.org, Matias Ezequiel Vara Larsen , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Wei Liu , George Dunlap , Julien Grall , Stefano Stabellini , Dario Faggioli , Anthony PERARD , Andrew Cooper References: <90a551bc-ffda-6db8-775b-11c100bf6f52@citrix.com> <20230306142315.GA745324@horizon> <20230308115410.GA1108824@horizon> <20230309103825.GA1221165@horizon> From: Jan Beulich In-Reply-To: <20230309103825.GA1221165@horizon> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR0P281CA0067.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:49::21) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|PAXPR04MB9232:EE_ X-MS-Office365-Filtering-Correlation-Id: bf62c889-aacc-4cbc-1e3b-08db209475b4 X-LD-Processed: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba,ExtFwd X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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:VE1PR04MB6560.eurprd04.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230025)(396003)(39860400002)(366004)(376002)(136003)(346002)(451199018)(36756003)(8936002)(5660300002)(7416002)(26005)(6506007)(53546011)(38100700002)(83380400001)(186003)(2616005)(54906003)(86362001)(31696002)(41300700001)(6916009)(316002)(66476007)(66556008)(4326008)(66946007)(8676002)(6486002)(6512007)(478600001)(31686004)(2906002)(43740500002)(45980500001);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?VlRicFZjTENvMGhYS1VTK2FGVThKOGFoSDR2NHpKSm1HbmdLVHpkOSt5TmZ6?= =?utf-8?B?V0NrcDRaMUd4S3cxQ2VKaGJMWG5YSFZuSHIzemRQT3Jtcmwwbk9NWklCTjRQ?= =?utf-8?B?Qk1xUnJYREkzSmVmNE8yZTlwenJvZ1JiOEFveVNpM1NXWGNPK1ltOGIrR29j?= =?utf-8?B?djZ6cGxLSUY2N3JKNXVtYWR2ajZld0tPZEUzT1R1Q25WYnpHVFliV3BlM3U1?= =?utf-8?B?RkZyTEpuRjBHQzdFZExrL1pGc1B6WjNYeitsUS9mQWZiTU9RVjRTUFdnMmg4?= =?utf-8?B?OGFhaFZTclhKSktMcGNyUlUyekVoRjQ0SkFRYmphZitsTVFtZ3pNUXBQeFJv?= =?utf-8?B?MkhiM3ZjSXVsWWhqeGpYcU1HTWxBL3RkRVE5cUUyN0pzR2VCNXlha2RsUUdQ?= =?utf-8?B?MTNJV0dhZHpCRFhvemh3cklYQlg5aHV0bU5rdHpucmhITDNmbi9KcUxWSWtJ?= =?utf-8?B?K3d4U0VleHVXUzJQM1BZQk5HNXNaQXB2OXF0VldJeDg1QlQ2enRLMUk1SmJL?= =?utf-8?B?djJCZ056b3VUNXpGOFlLVkFHdVVxT3dkZHZ2MGFuMS84cmZnd25zRm9FUWpz?= =?utf-8?B?RStKN1VVeWR4T25QQWdjVGs2YlhxOHpRdjR3cnNESzdpN3R0Tzl6RUJyZ2tL?= =?utf-8?B?cXB2cTVyT3U1VjRtckFWYnhBVm95TDVqL3lZbFlqVTBObU5jK3lCT1JFZXRp?= =?utf-8?B?VmxqVnM2QWZrRHFaaXdSSW43SWp3TVVCWTFYYlM4WXlpZEQ4eUxZM0dzTVZK?= =?utf-8?B?MjhTTnBEdnV0WlRhVm9ob0RNYU9CMVVyMEJ4SkxxRE5ub1MzTlNaNGhlWUhk?= =?utf-8?B?M3pxd01kcm5iUEhveFNhTnB2L3hMdmpON2RRM1Niait3MWVzUURwT0tsbWVY?= =?utf-8?B?d1pMdDlJMnVWY3RLUDRXLzBHWWhQdFBVRXRkcHlZUUN2SnQ3QWVJc2ZwY1dS?= =?utf-8?B?VSt3aWR1S2FhQy8zTGNWdWt2N2RvNldLRWZiQnJONGJkRHRCWGdoWFpRRXRj?= =?utf-8?B?STljbFBuaWlUT0FtSkpjVjdtWDVSVFg5alZxS2V1c0E3UVg2ak5hQVorZTZu?= =?utf-8?B?aDMwV3lkSy9oVVh0cDZvRWM1Y3A4aFpLOHFlVThybVpCa1lmTGx3S2NjOGdi?= =?utf-8?B?Rk9UWHhGcEpjbkJEY3hsS3JXMjhtNWtqSGhZMnVuSklrekVwRHc5QjVvWFZh?= =?utf-8?B?SUc5T0VmalVWMUZmUEhwaGw4YU1YWk53aC9sN0RybC9iZU55V0FLeDdIODZu?= =?utf-8?B?cE1xOU5kQXIraWluNDRRM1hxT3RJQWp5SXY5RXE0K0U5L2wxaDNiZUV2ZXR3?= =?utf-8?B?a0pxbGdJOG9YMlRpYWl3UnI1blpRYXJJY0V5WlpGM2pqNGlhTzJ0ek5rUzZI?= =?utf-8?B?V0JqdC9iOFRxV2xLRU50N3l0QTNDYWJWNkx5QmRQVU9iaUVLK1ZSa1RBOVlW?= =?utf-8?B?cTF1OGpNaXZuTE0rNEw1UE1Oem4xZFpaZFBGbXJSb3ZabnFvV0hkRFV3ZXRM?= =?utf-8?B?d3laei90cW92blRDamFtamRnbG5HWG5hYnpmemh1YzRaUGRPZlRMcnNLRmly?= =?utf-8?B?QlJqckpWOVlyOHBEeHh2UEdjNWxKVmIvRHVUc05xWW9rS05laDVrbm9lNHBI?= =?utf-8?B?VXFMckt0eFVkNC9zckJlcVZxelNsd0h5WEFDSkdHNTZZSWhhWHJENnFBRDJL?= =?utf-8?B?TmlJeE1VaHdqdmtkVEUrSGVkbEpkRFJXRGtwSnRoVDlwZllSSGtWT2QvczV1?= =?utf-8?B?eHJOdGxack90Q0Y1THVTdkNEdU1LZUQrRUtNUW5yM1NhcStDZzAvbnB6TWNV?= =?utf-8?B?SW1nbGIydEN6MHJRcHhHVDRJQjFnVkJ1U3NTaE5DcXR0bm5PRDRzNTFmcjln?= =?utf-8?B?K3FSQmphMU1kWnJNNnczOW0rcDdRMmp0L3l5Q3N1R2dqVlYxWXA4MVQ5V1N0?= =?utf-8?B?OHcrRWl2UzVqVWJ0UVJqaFdXN1VQTW9tMkJpOWdOalVsZWxMZ29rOGtEVnR4?= =?utf-8?B?VXV2Q0hxU0ZyeVlLRnpxMFNlekc5VFRyWVZVbWgzVHdwNnkraFhYRVJhVDcx?= =?utf-8?B?NER1cXBscDJpSTlnQVZQVHNaVTJWeVEvQWcrNTkyNW9WbWFVSmJnS1F0UHJu?= =?utf-8?Q?Bnc6kbvldBe/juqh25wQJmSL+?= X-OriginatorOrg: suse.com X-MS-Exchange-CrossTenant-Network-Message-Id: bf62c889-aacc-4cbc-1e3b-08db209475b4 X-MS-Exchange-CrossTenant-AuthSource: VE1PR04MB6560.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Mar 2023 11:50:20.7075 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: ekXAxTKlJcMGOlgfiaXtPiDPhiKKTI5eOpvVySLU4LmjQF++DeWVeU2l+YN20A8RtkezYoO/k58g6wsWfamcZw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAXPR04MB9232 On 09.03.2023 11:38, Matias Ezequiel Vara Larsen wrote: > On Wed, Mar 08, 2023 at 03:16:05PM +0100, Jan Beulich wrote: >> On 08.03.2023 12:54, Matias Ezequiel Vara Larsen wrote: >>> On Tue, Mar 07, 2023 at 11:12:00AM +0100, Jan Beulich wrote: >>>> On 06.03.2023 15:23, Matias Ezequiel Vara Larsen wrote: >>>>> - Xen shall use the "stats_active" field to indicate what it is producing. In >>>>> this field, reserved bits shall be 0. This shall allow us to agree on the >>>>> layout even when producer and consumer are compiled with different headers. >>>> >>>> I wonder how well such a bitfield is going to scale. It provides for >>>> only 32 (maybe 64) counters. Of course this may seem a lot right now, >>>> but you never know how quickly something like this can grow. Plus >>>> with ... >>>> >>> >>> Would it make sense to define it like this?: >>> >>> struct vcpu_shmem_stats { >>> #define STATS_A (1u << 0) >>> ... >>> #define VCPU_STATS_MAGIC 0xaabbccdd >>> uint32_t magic; >>> uint32_t offset; // roundup(sizeof(vcpu_shmem_stats) + sizeof(uint32_t) * nr_stats, cacheline_size) >>> uint32_t size; // sizeof(vcpu_stats) >>> uint32_t stride; // roundup(sizeof(vcpu_stats), cacheline_size) >>> uint32_t nr_stats; // size of stats_active in uint32_t >>> uint32_t stats_active[XEN_FLEX_ARRAY_DIM]; >>> ... >>> }; >> > > The use of stats_active[] is meant to have a bitmap that could scale thus not > limiting the number of counters in the vcpu_stat structure to 32 or 64. I can't > see other way to have an unlimited number of counters though. > >> Possibly, but this would make it harder to use the interface. An alternative >> might be to specify that an actual stats value set to ~0 marks an inactive >> element. Since these are 64-bit counters, with today's and tomorrow's >> computers we won't be at risk of a counter reaching a value of 2^^64-1, I >> guess. And even if there was one where such a risk could not be excluded >> (e.g. because of using pretty large increments), one would merely need to >> make sure to saturate at 2^^64-2. Plus at such a point one would need to >> consider anyway to switch to 128-bit fields, as neither saturated nor >> wrapped values are of much use to consumers. >> > > If I understand well, this use-case is in case an element in the stats_active > bitmap becomes inactive, i.e., it is set to "0" in stats_active[]. You are > proposing to set to ~0 the actual stats value to mark an inactive element. I > may be missing something here but would not be enough to set to "0" the > corresponding stats_active[] bit? The suggestion was to eliminate the need for stats_active[]. Jan