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Thu, 17 Sep 2026 15:57:12 +0000 Date: Thu, 17 Sep 2026 08:57:10 -0700 From: "Luck, Tony" To: Reinette Chatre CC: Drew Fustini , Adrien Ricciardi , Alexandre Ghiti , Atish Kumar Patra , Atish Patra , Babu Moger , Ben Horgan , Borislav Petkov , Chen Pei , Conor Dooley , Conor Dooley , Dave Hansen , Dave Martin , Fenghua Yu , Gong Shuai , Gong Shuai , , James Morse , Kornel =?utf-8?Q?Dul=C4=99ba?= , Krzysztof Kozlowski , , "Liu Zhiwei" , Palmer Dabbelt , Paul Walmsley , Peter Newman , Radim =?utf-8?B?S3LEjW3DocWZ?= , Rob Herring , Samuel Holland , "Sebastian Andrzej Siewior" , Vasudevan Srinivasan , Ved Shanbhogue , Weiwei Li , yunhui cui , Zhanpeng Zhang , , , , , , Subject: Re: [PATCH v7 2/5] riscv_cbqri: resctrl: Add cache allocation via capacity block mask Message-ID: References: <20260901-dfustini-atl-sc-cbqri-dt-v7-0-ca2935d85622@kernel.org> <20260901-dfustini-atl-sc-cbqri-dt-v7-2-ca2935d85622@kernel.org> <8230dae2-2cb0-4b46-8cec-dc4e281d4e4a@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <8230dae2-2cb0-4b46-8cec-dc4e281d4e4a@intel.com> X-ClientProxiedBy: SJ0PR03CA0226.namprd03.prod.outlook.com (2603:10b6:a03:39f::21) To SJ1PR11MB6083.namprd11.prod.outlook.com (2603:10b6:a03:48a::9) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PR11MB6083:EE_|SA0PR11MB4574:EE_ X-MS-Office365-Filtering-Correlation-Id: ef94e149-9c2f-4b4d-578b-08df14d4561d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|376014|1800799024|366016|7416014|4143699003|10067099003|3023799007|6133799003|18002099003|22082099003|56012099006|11063799006; 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A level > > whose controllers disagree is left unexposed. Other levels are > > unaffected. > If I understand correctly, while attempting to translate to resctrl terms, > this means that a cache resource with several domains may support different > capacity masks in the domains? > > I believe the "single cap set per rid" you refer to is > /sys/fs/resctrl/info/L3/cbm_mask and /sys/fs/resctrl/info/L2/cbm_mask that > exposes a single capacity bitmask representing the maximum allocation. > > As you know, resctrl is in the process of changing the way in which schema > formats are described. The most recent PoC [1] added new bitmap description > files but it kept a single value "max" file to describe the highest allocation > possible for a bitmap schema. > > To support asymmetrical cache instances it looks like changing the interface > to describe the maximum per domain (instead of one global value) could address > the gap? > > For example, if there is a hypothetical system with two L2 cache instances, one > with a 0xFF max CBM and the other with a 0XF max CBM then resctrl could expose it > as: That sounds like the not-at-all-hypothetical Intel hybrid client parts where P-core and E-core have different L2 masks. > > # cat /sys/fs/resctrl/info/L2/schemata/L2/max > 0=ff;1=f > > The schemata file currently and will continue to display the allocations per domain. > > resctrl will need more changes to support different CBM per domain internally and > until then all these CBMs will be the same, but adding this change to user interface now > may set resctrl up to support these systems in the future? I think Fenghua once worked on patches to support this. But I don't think they were every posted to LKML. One of the open issues at the time was how to handle the info/L2/cbm_mask file. > Reinette > > [1] https://lore.kernel.org/lkml/d258a32f-12d5-464d-abe9-4720fb3e44b3@intel.com/ -Tony