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Date: Tue, 17 Feb 2026 12:46:29 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Julien Grall , Stefano Stabellini , Anthony PERARD , Michal Orzel Subject: Re: [PATCH v2] domain: skip more stuff for idle's vCPU-s in vcpu_create() Message-ID: References: Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: MR1P264CA0171.FRAP264.PROD.OUTLOOK.COM (2603:10a6:501:55::12) To CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH7PR03MB7860:EE_|DM6PR03MB5356:EE_ X-MS-Office365-Filtering-Correlation-Id: 94da567b-533f-4a93-89ef-08de6e1a32a9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024|7053199007; X-Microsoft-Antispam-Message-Info: =?utf-8?B?Q3hzZUJWUFc5OHlZM2tJYXVLak9YV1pmUFF0MlRxQldxMkpETVdHSmszOWNh?= =?utf-8?B?SUZJUVBRaVpKOWdnZVhVNFZUbHdhUTVISXNvOE1UNStxb2xPRWNsNm1udkMx?= =?utf-8?B?WWQ4ZnFPcENVYmNON3A3S24yWGlzd0djZ0xkL3U4UExZUldsTDExdkZWNEFY?= =?utf-8?B?RVVPa1VNNDBIVjJnS0twRGpZYnRUQThwT3F6QzlXRTh2V3VpRC9hWkVIVnAv?= =?utf-8?B?SmhHK1pKcXMyb1JCUWZtVlkrUVl1Y2t2b0tFM2ZrZFRIY3BvOWNnU20zQUc5?= =?utf-8?B?dW9JbHdFWjFXUFZpQ00rYTdwUXc2QzJVQ3prTG5rZXVoME9RMXloTERjTk5U?= =?utf-8?B?cExpSUJsdmVmWEVpYVpMUXZGN2d6UnZPemhVaS9pQjBmZDFPSUFOWjZRR29G?= =?utf-8?B?cVBCODVCRWUvUjRYOXN5RW1iTEllMU82SEt1VVh4VFVrejlzQ1VjZkh0M0RB?= =?utf-8?B?Mnp2Zzhjc2JBVlVhUFRBUXlKbWthMHJ1MWlrUW1wTnpMWm14K1h4UnZnQXVj?= =?utf-8?B?WCtCbHA3SDdDYkx1NTRJOUIyOFlmYkhqVVR5cm0yeWNyOWkzWk10aHVwYTFP?= =?utf-8?B?c1piV3ZiUDZnTHJWV3FOUTdPSGEvbFYwRXQ2bmVrODE2VFVuWWZRNHRNeFdx?= =?utf-8?B?bzJUdXp0MHI3c2tCMEd5QUtpWDh3Y2lJV0kwMjA0alJsN0dPOC82N0ZqUXF2?= =?utf-8?B?aFRlQ2RTNTVSakhJV3pXdTh5QzhaME0xYWlZOHJxV3FDOTdmNmpXVTFlNGVh?= =?utf-8?B?TG5XZ01PcEs2T1hiaEhTN0FEQzB6K2ZydTYxcFFEbElIaGhtejBXRWhEOHJu?= =?utf-8?B?TVRCZ0o1WWJydXE1OTQ5a0hYWDFCSWRXM1FvV1lMRXNTTG1BcEU4QlFCWXVX?= =?utf-8?B?aDBNMW1mZG1Ka0hvL1JHbW1obHV3RE1oRWliNStOQTZtQ3hVc1o0UlpmYStT?= =?utf-8?B?ODdKQTVyd0cyRklmWkVZbWtzM1puR0VxdVN0R1ptdEpIZXhRZU9lVFJONmFM?= =?utf-8?B?b3F3QXpERzdtWE81czVDeWNMTEJrd2lQOXcwWXZqaXpCY1l1Vm5ickZmMVRs?= =?utf-8?B?QjhJVDd3U0d4SEhMQ2dIY29XUVJrOXFVbEwyT2R1Vk1GRXZDNmNjQ0ZsZVZw?= =?utf-8?B?T014UmJidVpSbzhjREYzVWQxaVI1Y2dteUFkT2x5RWxZSHZ0UkVsdE1UNFQ5?= =?utf-8?B?SnVhR1pWTjZ5c3NIdDBJVndoQVZvNnk5SmpVNlcvV3BBcjhVQzRRdXhQS2F5?= =?utf-8?B?S1c1Wkl2TFRZaHFDMEk0eXdiYnR0bnhHQ2kxTldIZ1BvQzYzK2lRRWdpYkF3?= =?utf-8?B?aGsxSkFDcnVkbmdCK3QxMzVBWkpLeWNEL3ZzRzd3NCtaaVpFYUdjQnJmTTFH?= =?utf-8?B?WnRIemxwZEVOZkY2aUlPUU5FYTRhWkk3cXgyU2lEbU5ibFBTWVA5UFZDKzIz?= =?utf-8?B?WDRNeXV0MXZ6OWNFd25ZbnR4UlZlcXZNODgxVFlDOEtNK3JzU25GWTlUVUVW?= =?utf-8?B?SWh0TWIrS1RDeHlzb3dOaHIxYThOV0NPbWtZeTVCS0owbW9UclpzWTE0SE1s?= =?utf-8?B?Um95cmhaQS95STY5QjFqSnR6VUN2clpMaEhyOEpESDNVeGl6U0pXaWJVY1dZ?= =?utf-8?B?RnN3dlp0UE83dVk1Mlg2WjBrdGw1cnFEcThUM3JvOE9LS1N4TkpTNUZvR2hn?= =?utf-8?B?Z1c3cE5QWEo4RTVGbm9sb3paMXZDUnVFdkxLWUErazhNenJvWWJvRjRudlM3?= =?utf-8?B?NWY0UGJpejVOcHRValFBVDJFYTNWalh0UWhnVGxqbndQcE5RaHpLRmZPMzYy?= =?utf-8?B?UjFhNTY0dkpvQUNQcmhKRi9Ca2UxZDF1ckpyaTR5Z3M4cUpDKzU4SlY5RVRt?= =?utf-8?B?d1FnMERvWU5NOHNBYk9abUVDU2xISmxvQ0dBRkFSYll6NVNXb0lIYVQyTllD?= =?utf-8?B?UFV0cmJKSEN0aXhvOGdiUHIyakorRXpMek1KR2hvZitOOEh1NHBKYlVxODhO?= =?utf-8?B?VnF4d1g4bVZJWnJQTHhuTldKblRHczhiWEo5ZDM3T2tjMm1SSlRxUklMZk1i?= =?utf-8?B?QVNaRmtrTTRtU1FIN2lMREpqTGZ6MzdET2twUS9BSWFRcVlFNm0yWHhxaVA2?= =?utf-8?Q?GHBs=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)(376014)(1800799024)(7053199007);DIR:OUT;SFP:1101; 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Nor do we need to > >> check whether the idle domain is shutting down - it never will. > >> > >> Signed-off-by: Jan Beulich > > > > Acked-by: Roger Pau Monné > > Thanks. > > >> @@ -516,7 +516,8 @@ struct vcpu *vcpu_create(struct domain * > >> } > >> > >> /* Must be called after making new vcpu visible to for_each_vcpu(). */ > >> - vcpu_check_shutdown(v); > >> + if ( !is_idle_domain(d) ) > >> + vcpu_check_shutdown(v); > > > > I would possibly leave this as-is. I agree that the idle domain will > > never shut down, but it's possibly best to needlessly call into > > vcpu_check_shutdown() for the idle domain rather than adding the extra > > conditional for the common case? > > I'd prefer to keep it conditional: Calling the function for the idle > domain gives a wrong impression, plus it may be the only one where the > shutdown lock is used for that domain. We may want to make lock init > conditional in domain_create() as well (possibly with other things we > needlessly do for idle or more generally system domains). I've been thinking about this, and I'm not sure whether it's the best approach to avoid initializing locks or lists for the idle vCPUs/domain. It's certainly good to avoid initializing stuff that consumes memory or other resources, but skipping plain initialization (iow: setting of values) of fields that are in the respective structs seems dangerous to a certain degree. If for whatever reason we end up with stray calls from the idle vCPUs/domain into functions that use those fields it's likely safer to have them initialized, rather than tripping into some uninitialized pointer or deadlock trying to acquire and uninitiated lock. Thanks, Roger.