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Tue, 3 Oct 2023 23:23:58 +0000 Received: from PH7PR11MB5984.namprd11.prod.outlook.com ([fe80::e9ca:a5a7:ada1:6ee8]) by PH7PR11MB5984.namprd11.prod.outlook.com ([fe80::e9ca:a5a7:ada1:6ee8%5]) with mapi id 15.20.6838.029; Tue, 3 Oct 2023 23:23:58 +0000 Message-ID: <27f1581d-43ab-4ab9-b6ee-b591d82c30b3@intel.com> Date: Tue, 3 Oct 2023 16:23:53 -0700 User-Agent: Betterbird (Linux) Subject: Re: [PATCH v3] cxl: Add committed sysfs attribute to CXL decoder To: Dan Williams , CC: , , , , References: <169575398814.4028282.11591056324662123995.stgit@djiang5-mobl3> <651c98472dfed_ae7e729495@dwillia2-xfh.jf.intel.com.notmuch> Content-Language: en-US From: Dave Jiang In-Reply-To: <651c98472dfed_ae7e729495@dwillia2-xfh.jf.intel.com.notmuch> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR03CA0035.namprd03.prod.outlook.com (2603:10b6:a03:33e::10) To PH7PR11MB5984.namprd11.prod.outlook.com (2603:10b6:510:1e3::15) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR11MB5984:EE_|MW4PR11MB6885:EE_ X-MS-Office365-Filtering-Correlation-Id: 65efebeb-5edd-4a57-dbc8-08dbc467d151 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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This is only a snapshot of the >> state, and doesn't offer any protection or serialization against a >> concurrent disable-region operation. > > A random thought occurred while realizing that the kernel uses a check > of: > > port->commit_end != -1 > > ...to determine that a given port (switch or endpoint) has committed > decoders. If the goal here is to determine when it is safe to disable an > entire memdev maybe it is better to check all of the decoders at once at > the port level rather than one at a time. It is already the case that > CXL prevents decoders from being committed out of order so what do you > think of replacing decoderX.Y/committed with portX/decoders_committed, > where it just does: > > down_read(&cxl_region_rwsem); > sysfs_emit("%d\n", port->commit_end + 1); > up_read(&cxl_region_rwsem); > > ...and cxl-cli aborts destructive processes on that attribute being > non-zero. Seems reasonable. I'll rework the patch and the cxl cli code. > > Is there any use case for userspace to check for individual decoders > being committed? It can infer "decoder committed" from "decoder_id < > decoders_commited".