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Petersen" , "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 05:23:50 +0000 Message-ID: References: <34cd22d6cec046e3adf402accb1453cc255b9042.1610207523.git.asml.silence@gmail.com> <4d063dde-c710-44e3-31b9-8fb6b7e1d952@gmail.com> <68887abc-2ef4-035e-625b-84569c1b5b24@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: 9c4c04be-41c5-4666-d7c7-08d8b5f1147c x-ms-traffictypediagnostic: BYAPR04MB4039: x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:5236; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: hDSsu2AWpng0Il9L0aaHa1c0PnS/btWnqAO01CR9ndkWWB4LwqtD74aLxHOFIdt0qgvK9x41W6WIOlgJ4BuZURtIPgmfDVCcXpskIa4HgUt/LHeP1YI1Z/Rtwry6Qh/ZKpr86MToRQMsDiqqxszPmZ5r5BuUZjnn6pL+IpXg1vatACHITDN8FnREp2apSiYRDl33qsLi1ldLaxBnkwzOKeWaK+ymYAEek34bN9lPRi97AQGq8sFZxQNZANoi9NddMyibRPmQyhsHNinTRXHtzsjAmNKiC+YNVZkFPWqEJtAsBOECdzm7dhWSqIWziiOzDevefZ8PA9q2iOHvkbrcf9F2isvGgG1jvoGKrDWkW98tGWfMxd243XUQ+yynlvowf3EzYiU+tRmP/SyAKZyfhA== 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)(136003)(376002)(366004)(346002)(39860400002)(396003)(83380400001)(53546011)(66556008)(6506007)(64756008)(316002)(8676002)(54906003)(66476007)(66946007)(5660300002)(76116006)(478600001)(71200400001)(66446008)(55016002)(2906002)(9686003)(8936002)(52536014)(6916009)(4326008)(186003)(7696005)(33656002)(86362001)(26005);DIR:OUT;SFP:1102; x-ms-exchange-antispam-messagedata: =?Windows-1252?Q?oF98f1p+LMDlvHN28CxE9Ri02UhDI0Pirt4zLkaraRAXOvaClVZsuwNJ?= =?Windows-1252?Q?GojheJhjVHF4KskVPf3ES7tXVWqjqPWhLTM1FEBsy3ktYj0hH9A2k1OR?= =?Windows-1252?Q?D7sRlmYcxZ2VPvKXELrThFhP3IR0qyIQx6wnQ5mbGyGfEZsr5KKtNSxa?= =?Windows-1252?Q?O1NxQM3f0r10FkQMlHqHJsLdj9jrnEZdBES84J+GmPPbDyEPFJ62HaNr?= =?Windows-1252?Q?Q8TJPanrUXJdWm6lVm7T9SXix0x/98gNCkT0pG8i+DkmdGam/bcRvbYh?= =?Windows-1252?Q?K70rAqXVdB+6fXLy6l+p3ifKs/CzXHiWznxI/Azzby3uyOLatnxHGohO?= =?Windows-1252?Q?QIJDSivu8g+EmPJPGmWElhD6V9rVCiyN6jrrQIdKlzFC8QzwP02T3Ugs?= =?Windows-1252?Q?qdT0ylNhj07IVES1K9OTKALQkkj1bnFvYx6CxiJMzzysiRlImr/X+reG?= =?Windows-1252?Q?DtkN7MdUPP+RzMNH/68TmjbNTXBgJjRIVPoyDwHvbuxCRk+2WCX4/1DI?= =?Windows-1252?Q?P1c20WkKOHhBbjkITKN0pkknuEJXbN1iIpmGUljuUKsIBDQdWIXYw5sR?= =?Windows-1252?Q?158e6YUozTfnGyU7CFva6LdNsHxL1lLqudybELqRhZfUFiHKQuVH0k/j?= =?Windows-1252?Q?XHZoLYvD2HIfaLpi/FvrRT8ny4/da3hobaba599UCVl67NNWq1YI+1eK?= =?Windows-1252?Q?pXKi7pkpJu6AgLtX6/ibFzu5Iwp0uOXzeDfLG9jwc4842e41RkR1pb5n?= =?Windows-1252?Q?7YfMDWXsiKMYy2Bu+kRIfaojJ3cCvW9wxZNOlOSoBIy85Ar3uxZyXdc1?= =?Windows-1252?Q?aqFzzwNdcpZe9PCVYZbTTKKJTa8u5pK2yNYBmoL3VABmWcvcjU38AqXf?= =?Windows-1252?Q?FnjSq7+2hH6xqnmRn1YMlZTFaJDzpfH37vu1BA4HWThzVUsU/9hJGpt4?= =?Windows-1252?Q?FpJGi973G5NtT/Sh246xwVVUvS3ep0npVhE5B0VURjmK1K5BRHckW8qa?= =?Windows-1252?Q?q3YOlQdoE6pRpQeLqB/X7KiDak/v9Xh5ZtN//vwK+p+JNvCG28KZdgQn?= =?Windows-1252?Q?/Gr5ZeRBEpLQTnft?= x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="Windows-1252" 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: 9c4c04be-41c5-4666-d7c7-08d8b5f1147c X-MS-Exchange-CrossTenant-originalarrivaltime: 11 Jan 2021 05:23:50.7488 (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: REG/LQIMpUcc3hQ/QpJTorPCo/Dk1ev7NsKjjocFi2ebmaOrcfbnfQPv4m4zCS55weQYFeNjlcCirft1E1SouTLuIo6BzQGTYxol6pWSgr8= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR04MB4039 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/10/21 18:32, Pavel Begunkov wrote:=0A= > On 11/01/2021 02:06, Chaitanya Kulkarni wrote:=0A= >> 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= >>>> 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 explain= ing=0A= > And then you see "Optimizations usually aren=92t free but trade-offs=0A= > between", and the patch doesn't fall under it.=0A= First part applies to all the optimizations with and without tradeoffs=0A= "Quantify optimizations and trade-offs."=0A= The later part doesn't mean optimizations without trade-offs should be=0A= allowed without having any supportive data.=0A= >=0A= > Let me be frank, I see it more like as a whim. If the maintainer agrees= =0A= > with that strange requirement of yours and want to bury it under=0A= > bureaucracy, fine by me, don't take it, I don't care, but I haven't=0A= > ever been asked here to do that for patches as this.=0A= I didn't write the commit log guidelines, as a reviewer I'm following them.= =0A= The patch commit log claims optimization with neither having any data nor= =0A= having the supporting fact ("possibly no observable difference but in the= =0A= long term it matters") for the completeness.=0A= > It's not "I cannot" but rather "I haven't even tried to and expect...".= =0A= > Don't mix, there is a huge difference between.=0A= Then provide the numbers to support your claim.=0A=