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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: Sat, 9 Jan 2021 20:09:15 +0000 Message-ID: References: <34cd22d6cec046e3adf402accb1453cc255b9042.1610207523.git.asml.silence@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: 7233df04-2f24-48b9-1efb-08d8b4da70c7 x-ms-traffictypediagnostic: BYAPR04MB4871: x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:5516; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: H45skPl+S03Koge4SshfddwlakZjek0PXEsDXJ2yNyxy41U4S/zuyBYbZFeVApShypd0FPu+YX/hVkEoqRC4YDCBiSIhiemF3ldpwPbEqRJuZV3erg9iYIJvIO+R1oVe0SBoHQv1rN1q8uho8pdG/GteeloQHHaRfOMtg863k/0o2dnrVzR5mz14JOcfVX2mWWdI51o3fP2ciFz2hz/7Ec/qpOGy/qVnRqkw1jcK7d5dAD9tMhtYgVThOiq328KJk34NpuUtXzK9n3rOc6NNytOK8hjSFIAGYG4rei582B6p8q6MDx9QHXoh87PQNLDMmPe5ikbwYuVvvgiHuoXyg8kOBjt2yWQy5GTbFfwqwAe1ncL6FgL/WtFwgjjVYLp/csU8tv2PZS5lRZwzQ17dxQ== 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)(346002)(396003)(136003)(39860400002)(366004)(52536014)(8676002)(2906002)(316002)(110136005)(66556008)(66446008)(66476007)(54906003)(64756008)(66946007)(83380400001)(5660300002)(478600001)(9686003)(7696005)(26005)(6506007)(4326008)(53546011)(76116006)(8936002)(33656002)(55016002)(86362001)(71200400001)(186003);DIR:OUT;SFP:1102; x-ms-exchange-antispam-messagedata: =?us-ascii?Q?0o8ZchHg/cU7s3PeoV4KLo5jz6jjmT0UIK055g6WeQ9cqwkhQhzEcyJMdDyp?= =?us-ascii?Q?WMHLk/KHXqd0iJkoWWKEY0t0KwD0jEewhQkA6KnBAMTCYut5ACOWtmsviwma?= =?us-ascii?Q?IW4r6WoPPmavVT9120pdc0mgLLwcSHtr3MfwdVyOo5Ph9Mv+O6HRhFGPJGvD?= =?us-ascii?Q?XGSJDFXajYC7/ivnc6GF6Kplvdstf6yJSDZzXV90ocS691AWmx4LHK7JIlU2?= =?us-ascii?Q?eB0e9+ZvQ3rmIeAqq+qc9mE98GEbicpUKzc+s9ibEX6OCC3tdgY7j62r5Qha?= =?us-ascii?Q?Uay0I/5f0K0FhvmFkMI4pTQuPxtrkXMgvO0waA+C2ed2qd+YbbWqT9i6Mzcu?= =?us-ascii?Q?I4ZCniw793HFL+cJ1OeicagVHMLAEFLZJWNBfUIJVRngC3YKGFliEdE15SgU?= =?us-ascii?Q?LQuz+/xYgCwz6d9WPOJ/aPdHcBYOHfATOgsCA/hza/WiPuL86XM+UgQ8+1J8?= =?us-ascii?Q?LQIyyicWQP/0Fgppdx2jzF6uClaUQaBvfTDL+wuLUXKdFoWgBNjMXX1PFcqZ?= =?us-ascii?Q?/XcB6j4cGqxrqg3KWJ6c+yAMH1RRFetX0NcOsdWnzVWRveNKx34SwD7RMPxU?= =?us-ascii?Q?OO6C9FbVN5JemW146AuN8YTeBLNQRkl8jdebrCHFHZ2Ne+hbyDsANeOvYDXa?= =?us-ascii?Q?rY2mVbZpIzHhPguJL2OsGy5VE03LOhzRSAIRlBy0xR26/1nfcvU8dMv04VDm?= =?us-ascii?Q?UYHwASNospGOr2/dVBrvuBf34RuKkfGhKbVTUYvquAEUguuYrkkhTyN8Zlzl?= =?us-ascii?Q?ovlqZ4+gnwdXegD2MagDxX9mTHq8Mwopk4pMn9cWo2nu9s1peWdnSAnPAWYz?= =?us-ascii?Q?afoOaWhaRj54QGznn4Fyi7yJ+Ne4aD6J9l+ucxNhvR7GTodwGJQX0gW1kSp2?= =?us-ascii?Q?fmppw3SqMEXqQHxkXbkXdjVjHepKeIgxmBQ0wZ7B9NxLsHecJ7/ynwAcaDZI?= =?us-ascii?Q?P7QZyV3+ypnvjpFiMybj1dpVHKlZss1vtmSY6RVdZas+qo7vbAGju9/HQGg1?= =?us-ascii?Q?uYCW?= 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: 7233df04-2f24-48b9-1efb-08d8b4da70c7 X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Jan 2021 20:09:15.9645 (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: E9hJwFVATk8GPm8tBhApZ/WqnBjCEfPVasMz+iY8CmGqhHz4y/DB2GTtrL1LsG2cathB60aIV2+Thd8UvhuwVB93M4baDNnhi9JDTBt5DsM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR04MB4871 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/9/21 07:59, Pavel Begunkov wrote:=0A= > iov_iter_bvec() initialises iterators well, no need to pre-zero it=0A= > beforehand as done in fd_execute_rw_aio(). Compilers can't optimise it=0A= > out and generate extra code for that (confirmed with assembly).=0A= It will be great if we can quantify this optimization with the actual=0A= performance=0A= numbers.=0A= > Signed-off-by: Pavel Begunkov =0A= > ---=0A= > drivers/target/target_core_file.c | 2 +-=0A= > 1 file changed, 1 insertion(+), 1 deletion(-)=0A= >=0A= > diff --git a/drivers/target/target_core_file.c b/drivers/target/target_co= re_file.c=0A= > index cce455929778..5a66854def95 100644=0A= > --- a/drivers/target/target_core_file.c=0A= > +++ b/drivers/target/target_core_file.c=0A= > @@ -267,7 +267,7 @@ fd_execute_rw_aio(struct se_cmd *cmd, struct scatterl= ist *sgl, u32 sgl_nents,=0A= > struct fd_dev *fd_dev =3D FD_DEV(dev);=0A= > struct file *file =3D fd_dev->fd_file;=0A= > struct target_core_file_cmd *aio_cmd;=0A= > - struct iov_iter iter =3D {};=0A= > + struct iov_iter iter;=0A= > struct scatterlist *sg;=0A= > ssize_t len =3D 0;=0A= > int ret =3D 0, i;=0A= =0A=