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Thu, 20 Nov 2025 22:17:47 +0000 Message-ID: Date: Thu, 20 Nov 2025 14:17:44 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fs/resctrl: Consider sparse masks when initializing new group's allocation To: "Luck, Tony" CC: , , , , , , , , , , , , , References: From: Reinette Chatre Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0377.namprd04.prod.outlook.com (2603:10b6:303:81::22) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ2PR11MB7573:EE_|MW3PR11MB4537:EE_ X-MS-Office365-Filtering-Correlation-Id: ac490675-e1bc-436f-c0b2-08de2882a278 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024; X-Microsoft-Antispam-Message-Info: =?utf-8?B?ZUxCRTNzNm5IVjlrUDJXTFFsVmxJMHR0ZTE3eVRCeU5FQ2lMbEVXbTB2akFa?= =?utf-8?B?Rk9MMzVzQ2E3TWQvNVVvRDRzcDBTRTRKa3N1d1FhaXNPUkY2TVdaTTZYZVFL?= =?utf-8?B?emZPRkxyaGNTS1dxWnhqQi9WUC93NzFBZmwrbEJSR1U5SjYveVlUVnp5Vzdz?= =?utf-8?B?d2xqYnlXSUc0SGdQenEwSjh5MTZINmZFM3ovY1lQMmhFYlZjMGxTYjdVYUs1?= =?utf-8?B?MHlhR2p2dENySUJaM2lHakNOMHZIeDBmcllIUHBkeWVOMDZGaE9CYU1wUGR2?= =?utf-8?B?aWxzVTVPM05LM2swRitwazRHZTlMTEwwcm5FS2p6aldSNmZJbHVGUkxKLzB5?= =?utf-8?B?Qy9Wc3FGR2llVzlkR2EzVFVocTFUMXZOeWZ6VXM3dWNNOTlFR3BtQk1hUnMy?= =?utf-8?B?bUpxUUJJZWtDNzF4QlFvSWRKZDduekEwV3luS0RxTUtXTnphczFLYUVUaFl1?= =?utf-8?B?S0tSYnQ5ZG9MK1NKdFRIbDJYTFphUUUwcTk0OEZIcENWeFBaNHpmbkRvWm1o?= =?utf-8?B?YTE2aUR4KzlGU0N0SU8xbEJCWURocyszQ1hLQUhyb3RpN2ZrRUoyVTdCWitl?= =?utf-8?B?RXVmZkVJM0lXaWo0U0xCV095anNZUVNOelBJdVpKUVI0OFlxeTRBUVNvcWVt?= =?utf-8?B?ZDdvaTZCQzl3UTRSUG1TTEM2ZkdwRHJ2L2lMUzhjWVFlM3RsTEdKaVFocU9a?= =?utf-8?B?K2N0VzN2UTBDTEt5dTNKUko5Ymw5US9nd2xyVFAxTytQdGtKM1FvWjc3UllB?= =?utf-8?B?cHFEVGxWemU5Uk1PU0szSmwva3ZGZTh0SDFPU3MzaTJlL3FnR2RaQWpBVURG?= =?utf-8?B?VHNYSmVNRVlObUYrTDh0azZsTFhjVy9CNC9DbG9Rc0hVOUs2RmhJTHl2VzVN?= =?utf-8?B?cmovTkM0QUZjRGxBRmxKb2RrM2sydzh4dS85SkovZUJ4OGJoZDFuTTJuS1lQ?= =?utf-8?B?eTgyMUhSS3lyMlNLTm5YdnRjQSs3Ym84YjdWTTZpNkx2K1dHT1RCOHVEZnZI?= =?utf-8?B?LzBXMU9GdkF1Qkk3cC90RHJiY0YwbnJWMzAzMWNxL3NnMmNRRldwSXNNZlRo?= =?utf-8?B?RCtFckFDYTI4bk9qS1BwMm1QWC9ISFozSjBQalJnR0o2OCtZbnZVOVB3TStQ?= =?utf-8?B?THNyeFZOUzQzcExpVzYzcml2ak4wZHdqR0Nwa2tYd25ZbkJ6dHplT1lHaGU5?= =?utf-8?B?d2MzcHlRUlk3SCttNm1mMWF6bGY0SmYwU1U2ZlN3K0k0QzZBdnlZaUs2QkhQ?= =?utf-8?B?c205cHpYR1BFeXpjaFU2T0R5czFNeEZ5ZW5EVi9mR05zRHR3VGwwU1IxMnRV?= =?utf-8?B?UEd5c0hTTDNlUVZIMHB6eHRQejJpclFWL0pqNHZndkswdFNDbTcvQStsRjQ2?= =?utf-8?B?MWRRNnZZSTJVcGFlT3ZSeXJySE5BaW5kTElrRE9JczhoWEo1NFBkd0tJVWhM?= =?utf-8?B?cFJvYmhlbUVRYjBmamFrYzdzdGk3SEgzdVVTcnZtbnlPK2NiNzViem5vWEpK?= =?utf-8?B?c3pZcGczcWpwVENXZDNjNWZ4MXhqYUpxNzRFeWtLQnpsTXBXcVlXejJmOGJV?= =?utf-8?B?MkFVd29TU1dnZSt3cno2d3h1Z21WcU5JTXhabDJjQlIwcjdIR2JjM1Z3d3k5?= =?utf-8?B?RkVEeHUwaDZHbFZHYnFYT3d0dFFTUFFOQTRPTldNL2F3VjdWdDR5cWVnMkJi?= =?utf-8?B?M0RFcHBLMmdVdGxiN2hjeFYyaDc0M3lRWUx0bU5tejcrUjlXU1JuZktJZ083?= =?utf-8?B?K2VRQmgrN2J0TzU5OTN3Z29UMTJkVGk3SGRFRXJwWWxXVlltaG5xL1FIeXZF?= =?utf-8?B?MG15Y28xRFFUU29UdGpKWnc0emVkcDRqTi9qc1V1T20rYzZUWWtKS01sUVlE?= =?utf-8?B?dlhXZWtjSFdDN3pUejFKR0ZweVV0OEtxSnVKaDFxbmxIZ0U0cjUzbVplUmdZ?= =?utf-8?Q?jc564Ft8MfeMsoc1EFH1xltFcR+9jaQi?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:SJ2PR11MB7573.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(376014)(7416014)(1800799024);DIR:OUT;SFP:1101; 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For >> a cache resource this means all cache portions the new group could possibly >> allocate into. This includes unused cache portions and shareable cache >> portions used by other groups and hardware. >> >> New resource group creation does not take sparse masks into account. After >> determining the bitmask reflecting the new group's possible allocations the >> bitmask is forced to be contiguous even if the system supports sparse masks. >> For example, a new group could by default allocate into a large portion of >> cache represented by 0xff0f, but it is instead created with a mask of 0xf. >> >> Do not force a contiguous allocation range if the system supports sparse >> masks. > > Note that the allocated mask on systems that require contiguous bit allocation > is not optimal. In your example where the available bits for the new group > are 0xff0f, resctrl will focus on the least significant contguous range and > set 0x000f, rather than the larger group of bits 0xff00. Right. The priority, as supported by aptly named cbm_ensure_valid(), is to ensure the mask can be supported by the hardware. > > Fixing this would be more complex, and I don't see a lot of value as the > user is very likley to rewrite the schemata immediatley after creating > the new group. I agree this can be optimized and that it is not a priority (would appreciate to hear if there are different opinions on this). Users that may encounter the "less than optimal" initial allocation are the ones using exclusive and/or pseudo-locking groups where I expect user space controls allocations with care. > > So for this patch as-is: > > Reviewed-by: Tony Luck Thank you very much. Reinette