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Petersen" , James Bottomley CC: John Garry , Ming Lei , Bart Van Assche , Hannes Reinecke , Kashyap Desai , Christoph Hellwig , "linux-scsi@vger.kernel.org" , Sathya Prakash , Sreekanth Reddy , Suganath Prabu Subramani , PDL-MPT-FUSIONLINUX , chenxiang Subject: Re: About scsi device queue depth Thread-Topic: About scsi device queue depth Thread-Index: AQHW6DZDkGmGUhtJTUyXH1t3aSt6mA== Date: Wed, 13 Jan 2021 06:36:22 +0000 Message-ID: References: <9ff894da-cf2c-9094-2690-1973cc57835a@huawei.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: oracle.com; dkim=none (message not signed) header.d=none;oracle.com; dmarc=none action=none header.from=wdc.com; x-originating-ip: [2400:2411:43c0:6000:e53d:bea0:4863:19b6] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: e463ef3b-689b-42cb-cfe6-08d8b78d8b15 x-ms-traffictypediagnostic: CH2PR04MB6617: x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:8273; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: x42Sj2QXw3QKjf+eQ/7K9pcgq7vhpoz0b8Ud8ptCPYZGPERG3wwn+ricN7nao1AmCfR1VkdgGK3y5YlqNRMzQGFlcEG1S6kJkfd4JIMAZrSV5sj24IxV4U1P6z/ORRc7HnoqBFfBOwsEefe7Xk6SmoyC/J0H+ymDYHLpGG3ysykeGeqB3g8J8H+ntWWbjN2EKSy9P8eLZTX3bm4Ws+Fz97kY5FagsFuohU4mO/Qatt5mZVD4IPQ5qyggJl0ZVQ9JYxl+PZ3RG0M0yLnVvyV3jrN7nsecs1gW7H342+iYdGeuYagBONqf+iS7NHJ++UaacTQF/IQF86gPSg7aNcXdSJxGdt2kXs/5T/k9GgZl5LM43/VIOcTzqb5LAbecLdIWZme8QOjkUtDWEh4tMuimcw== x-forefront-antispam-report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH2PR04MB6522.namprd04.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(366004)(39860400002)(136003)(346002)(376002)(396003)(9686003)(186003)(91956017)(6506007)(55016002)(86362001)(66476007)(8936002)(71200400001)(54906003)(66556008)(66946007)(66446008)(316002)(5660300002)(110136005)(64756008)(478600001)(8676002)(2906002)(53546011)(52536014)(7416002)(76116006)(4326008)(7696005)(33656002);DIR:OUT;SFP:1102; x-ms-exchange-antispam-messagedata: =?us-ascii?Q?Kspej9Ut2hQwGqaWmDVgjebxTOriS74wPcJlnnREYq/557fFrU8UOmPUFd1N?= =?us-ascii?Q?kecclc5S3Sj5jO0O9v0fKqdE+AZxTH+7ACtmK0ms2UN31y39iuiO7hFufFdF?= =?us-ascii?Q?2157VRylYDNUpqhcUIwfj03F3jqgggQxRo2itWSaXbKjQQ1ri/twZxQI+gLn?= =?us-ascii?Q?WfvhgMOyeraFwaKEIfLPuMQJHymmwXXewf9wwAkZE2xybT0aQb4kn38jMgOk?= =?us-ascii?Q?7psJNzqU8zGzdwWIN4RBN0k5qiDnIJawmaHa7hCAVgT89ZLyNEkBpMJjfW3y?= =?us-ascii?Q?gf9VZa/oZDuCjHdpr4aTnIznuSpmIqD70u2wBMerMfVDywQ5Jsmd1gwSjsZg?= =?us-ascii?Q?e230BkjRFFfUrabsL3z4ZPJJ+f2VPh68djHQp9nXlwsdxwU/n1fMqfoJxvlo?= =?us-ascii?Q?ocvvIQwS5+l1BDx6NR8QatMu5VeGvZGuhPlghOFkAneqV7qH17obO9aBv7QS?= =?us-ascii?Q?/CvjEqHAsKRB1AnODH1/8PtMwlZqUghGu+MgUFL5Qxtw5RpgmwHUfEZDfAnd?= =?us-ascii?Q?nsT6YOnmJ8QNCTrAaIiwIG07/xnc/jSvCeVFJG/u0yZxBEFM9q0kXphKGqZl?= =?us-ascii?Q?oIBISniuwfED0cMYMY23c73Aj321VjXeFXSgdzsGQMezBDl6QfDzwYZSUkd8?= =?us-ascii?Q?PM6XBiDgrGk0AQgdwYzBxcjzMxlM0yesFFDDul0Nf1GAUVDk9X7bPp23uQSK?= =?us-ascii?Q?2moTYRP/E4fPcmUAAi7Y6/+AbP3lT4mR11/TBXv8QCSDT9awxXTsBzYLXBo7?= =?us-ascii?Q?4tdKThcBTyOsNks98QLtDX7MrXkc6Ug03uB8F+oYL7GTPQBDM5CgCU9UjtGk?= =?us-ascii?Q?7JjW6xqb3swDvhtWMqvSGY3dWMAcqxHzRckIzmFRO8+yvcqY8dzuOm20yW+n?= =?us-ascii?Q?dRX+y+8CeXvhmsRiNNuY1by1aAYk8ePhWO1d2e62ujurEF0y5LjBocAy51lo?= =?us-ascii?Q?PB6yDDd7OUwdlbuE+rKt/t6e6Q437cUrc3qzDywsdsCXCZTPGui8qfKEmGts?= =?us-ascii?Q?1fw8nnzEI8tef9g0H2L/90xx2qkWq0OaMm89bjB1KJ8xuvY7ycOzY/0hc5qH?= =?us-ascii?Q?AtuDtFF3?= x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: CH2PR04MB6522.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: e463ef3b-689b-42cb-cfe6-08d8b78d8b15 X-MS-Exchange-CrossTenant-originalarrivaltime: 13 Jan 2021 06:36:22.3345 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: bYnRTDFZ8UYmdZ7GpXY8NiNqHqgBI7zFa20YaeIoZHM9t3xdUywi0yG1/gzVdY9H2QOpYfYo2qwF0qd1G9n2wg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR04MB6617 Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 2021/01/13 15:10, Martin K. Petersen wrote:=0A= > =0A= > James,=0A= > =0A= >> A co-operative device can help you find the optimal by returning=0A= >> QUEUE_FULL when it's fully occupied so we have a mechanism to track=0A= >> the queue full returns and change the depth interactively.=0A= > =0A= > Many disk drives and SSDs only return QF/TSF when they are out of actual= =0A= > command slots (so typically 255). There is often a watertight barrier=0A= > between the transport-specific command processing and the media=0A= > management code. Very sad.=0A= > =0A= > So while the exponential backoff approach works great for disk arrays,=0A= > it's hit or miss with drives. And it's really hard to come up with a=0A= > good heuristic since the optimal queue depth is highly workload and=0A= > device-specific.=0A= > =0A= > We had a few folks looking at managing write queue depth based on=0A= > completion latency a couple of years ago but it didn't come to fruition.= =0A= =0A= And if IO priorities are in use... And there is the latency target specs co= ming=0A= soon to make things even more interesting :)=0A= =0A= =0A= =0A= -- =0A= Damien Le Moal=0A= Western Digital Research=0A=