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Petersen" , Bart Van Assche , Niklas Cassel , Paolo Valente , Jens Axboe , Christoph Hellwig , Hannes Reinecke , "linux-scsi@vger.kernel.org" , "linux-ide@vger.kernel.org" , "linux-block@vger.kernel.org" Subject: Re: [PATCH v3 01/18] block: introduce duration-limits priority class From: "Martin K. Petersen" Organization: Oracle Corporation Message-ID: References: <20230124190308.127318-2-niklas.cassel@wdc.com> <731aeacc-74c0-396b-efa0-f9ae950566d8@opensource.wdc.com> <873e0213-94b5-0d81-a8aa-4671241e198c@acm.org> <4c345d8b-7efa-85c9-fe1c-1124ea5d9de6@opensource.wdc.com> <5066441f-e265-ed64-fa39-f77a931ab998@acm.org> <275993f1-f9e8-e7a8-e901-2f7d3a6bb501@opensource.wdc.com> <86de1e78-0ff2-be70-f592-673bce76e5ac@opensource.wdc.com> <7f0a2464-673a-f64a-4ebb-e599c3123a24@acm.org> <29b50dbd-76e9-cdce-4227-a22223850c9a@opensource.wdc.com> <049a7e88-89d1-804f-a0b5-9e5d93d505f7@opensource.wdc.com> <4e803108-9526-6a75-f209-789a06ef52f9@opensource.wdc.com> Date: Mon, 30 Jan 2023 21:49:59 -0500 In-Reply-To: (Damien Le Moal's message of "Sun, 29 Jan 2023 12:52:30 +0900") Content-Type: text/plain X-ClientProxiedBy: DM6PR02CA0163.namprd02.prod.outlook.com (2603:10b6:5:332::30) To PH0PR10MB4759.namprd10.prod.outlook.com (2603:10b6:510:3d::12) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR10MB4759:EE_|PH0PR10MB7097:EE_ X-MS-Office365-Filtering-Correlation-Id: 40b2073c-7151-4766-53d3-08db0335da26 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Though I think it will be hard to define a set of QoS > hints that are useful for a wide range of applications, and even > harder to convert the defined hint classes to CDL descriptors. I fear > that we may end up with the same issues as IO hints/streams. Hints mainly failed because non-Linux OSes had very different expectations about how this was going to work. So that left device vendors in a situation where they had to essentially support 3 different approaches all implemented using the same protocol. The challenge of being a general purpose OS is to come up with concepts that are applicable in a variety of situations. Twiddling protocol fields is the easy part. I have a couple of experienced CDL users that I'd like to talk to and try to get a better idea of what a suitable set of defaults might look like. > This hint applies to all priority classes and levels, that is, for the > CDL case, we can enrich any priority with a hint that specifies the > CDL index to use for an IO. Yeah, I like that approach better. -- Martin K. Petersen Oracle Linux Engineering