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Petersen" CC: "linux-scsi@vger.kernel.org" , "target-devel@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] target/file: don't zero iter before iov_iter_bvec Thread-Topic: [PATCH] target/file: don't zero iter before iov_iter_bvec Thread-Index: AQHW5qBkaWm3Wnjfmk+XiYs/GS5+eQ== Date: Mon, 11 Jan 2021 02:06:11 +0000 Message-ID: References: <34cd22d6cec046e3adf402accb1453cc255b9042.1610207523.git.asml.silence@gmail.com> <4d063dde-c710-44e3-31b9-8fb6b7e1d952@gmail.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: gmail.com; dkim=none (message not signed) header.d=none;gmail.com; dmarc=none action=none header.from=wdc.com; x-originating-ip: [199.255.45.62] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 17a077a6-4864-4eff-b479-08d8b5d57835 x-ms-traffictypediagnostic: BYAPR04MB5334: x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:1284; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: KtfT562tRKKS4fyHR36t3HTlaGLemikqHg1JVI8n8uXfzqt+5ZyBCkxPDWvIx5zjYNJEDKo48bBwSymYaz6kHrwrQYiOYsDrnktDH4TdKN53iESNsOjlxDpDdjLsruPqKeL8yuFHHTG+z82Uu74797xQz7c4/+gVLfVTeD+abglio8Zpwsa7UMSP7Ajvjbjpw2xL1cMo/gShpFIe4QO8Cx7gGW6y80h9pHxgd7Gl2TkJIRccIDfMM/jkDsT7Nz7TzrMBirfVgedIMEpWa6N25Hc2XQYTruMq69GelqVMkcaf/bdADX1FXJCTbRodXsnfvgBTlMDJ4mR7T1F+QxjxW1pqF9/54lXcv3R+kBsME/98gdHXWyG2CWG3ynZqqfnsEbPsLYgsThch7wBbCikwYwZkC4yAezXp0LjwQi2WX5VhbyS9KDdjq1sCCDwFAlXmvsBh2G04+152l7XIHun3Kg== x-forefront-antispam-report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR04MB4965.namprd04.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(376002)(396003)(346002)(366004)(136003)(39860400002)(4326008)(83380400001)(186003)(86362001)(52536014)(26005)(54906003)(66446008)(478600001)(64756008)(6506007)(966005)(9686003)(110136005)(33656002)(8936002)(76116006)(66556008)(66476007)(2906002)(53546011)(66946007)(8676002)(316002)(5660300002)(7696005)(71200400001)(55016002);DIR:OUT;SFP:1102; x-ms-exchange-antispam-messagedata: =?us-ascii?Q?5mgma7cQmu5I4OhPoriBdHzVNJE0TQ9jrqTvZB64QoZQ6+Qt9JuflYFrVizU?= =?us-ascii?Q?jP5Pv34W0VIa9VdVJdAbtO5nefw/Zz6oVvN3K9iomdvSqeqkMuRldf8RcrhP?= =?us-ascii?Q?PbDiy1pERytbyhPhEPCIUJEDXgxNFaTqEwzUJU5cw/ktmhvcIB3NH3AxtENj?= =?us-ascii?Q?y0+yLxfmqUGrOkzoMRlGT3KSl7JFfIRx6ThclhbxANGFOnSYlvqr2VmcCerK?= =?us-ascii?Q?utenkoDnMManLxJFZriinkttibeDN79zjTRMERkIUBMe3Yizb4LDxvFCX51f?= =?us-ascii?Q?VFdFVJ/u2oC+mcrNm7saX8D09bxdGLC503Qf46jRR3ZbdDhzBxTrLRls3E4i?= =?us-ascii?Q?lwHb1oUZ9jMUd0GeurCrPJsBt7ndq42eY62Ud3E4cjmjNLjOv8XnVSAR7PfR?= =?us-ascii?Q?vxDaFsLS8ypSxPS81l3tsg3A1eZvsGtfM3YCZbo1eupDWDiNVD98/10aWPe/?= =?us-ascii?Q?IM+b/Iv0BuS1tNRi5cQ5gvte0ECJCqV4M0HYEdt+/onYLVi9qXiBo+cJqL51?= =?us-ascii?Q?E1HSTEIgN/brdzShiMw5NCfLid0yDbrfcqYnv5h/IH9W2pQBL2FOHwj8P5g1?= =?us-ascii?Q?bVW8cIaP4rVkF3UbuwBjgmPDtUO8zHHHMRElV0/etMeWXuteS1G3Ip4lujq8?= =?us-ascii?Q?FF75wt+A6ECUTq+tNyIjLq2DI8lj0WNNGoDQlH0t3uad1F4YL50cVkAl1Ws7?= =?us-ascii?Q?udk0CBud5fk82uWj6yE5vEB830CNqeBh8l9JpfYFzR5LQKkxvnqj8ro06wud?= =?us-ascii?Q?GylF6W4JNPeVLiyPm5wJk8ibpyI1+1Tj/l+9RceebajQf1UrccBf4BjG7jay?= =?us-ascii?Q?FAsqiMG00Jr9Alx+m204cHrW+d3SE7ObGk7+gaB62RqIFyWdNjiLqcY3QINr?= =?us-ascii?Q?MDXFfJVZoM3mjuuymVg3GYzVQPEtEBtJnUIIjEs8F4OweZr0/Y79Fu0iAV/6?= =?us-ascii?Q?LO3FsQhle+8+HHXcyR/vHpBV+Fl4D7OqK3W+INvptSEyRNKxhQc1l9a5vG+4?= =?us-ascii?Q?5U6h?= 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: BYAPR04MB4965.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 17a077a6-4864-4eff-b479-08d8b5d57835 X-MS-Exchange-CrossTenant-originalarrivaltime: 11 Jan 2021 02:06:12.1114 (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: 0qqlWQ0aoPkb0O/77uIvbdeFli0T5fs61zBKPB7Q0iQ45seJzB97jhiLGNPYZ0jFF9BP3l6GxxGOuu0r/ga7EgZ6/9Jxe3ZD7957GD/e3zU= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR04MB5334 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/9/21 13:29, Pavel Begunkov wrote:=0A= > On 09/01/2021 20:52, Chaitanya Kulkarni wrote:=0A= >> On 1/9/21 12:40, Pavel Begunkov wrote:=0A= >>> I expect you won't find any, but such little things can pile up=0A= >>> into a not-easy-to-spot overhead over time.=0A= >> That is what I suspected with the resulting assembly. The commit log=0A= >> needs to document that there is no direct impact on the performance=0A= > It's obvious that 3-4 extra mov $0 off(%reg) won't change performance=0A= > but still hasn't been formally confirmed ...=0A= This is obvious for you and me since we spent time into looking into=0A= resulting assembly not every reviewer is expected to do that see [1].=0A= >=0A= >> which can be seen with this patch, but this is nice to have=0A= > ... so if you don't mind, I won't be resending just for that.=0A= As per commit log guidelines [1] you have to quantify the optimization.=0A= =0A= Since you cannot quantify the optimization modify the commit log explaining= =0A= that there is not significant performance benefit observe.=0A= > -- Pavel Begunkov=0A= [1] https://www.kernel.org/doc/html/v4.10/process/submitting-patches.html= =0A=