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Mon, 21 Sep 2020 12:21:11 +0000 From: "Jakub Grajciar -X (jgrajcia - PANTHEON TECH SRO at Cisco)" To: Phil Yang , Honnappa Nagarahalli , "dev@dpdk.org" CC: Ruifeng Wang , nd , nd , nd Thread-Topic: [PATCH] net/memif: relax barrier for zero copy path Thread-Index: AQHWh/3EnG2VG7V/bUCs7pX4TLuPnKlvC/CAgAPLw9CAABpmAIAAH0Cg Date: Mon, 21 Sep 2020 12:21:11 +0000 Message-ID: References: <1599802699-20876-1-git-send-email-phil.yang@arm.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: arm.com; dkim=none (message not signed) header.d=none;arm.com; dmarc=none action=none header.from=cisco.com; x-originating-ip: [81.89.53.154] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 203ebc08-2f7e-4864-03eb-08d85e28d373 x-ms-traffictypediagnostic: BYAPR11MB3637: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8273; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: gluIIc+J6X4BHWtku+qcVz0CUld9PrKCSmfRil6avdxTKnw2o+cT9YLTN+/4MN07X9FhMxFVEtvJlE1LifDYp44nBl9d5ZprH8beF69MRojKxYxjFx/dGJ4t/B9QBXMdgg2mE9QuHZ+UQreTcP82PPAOA9gVmm38WfVxXcqLD/QpUJE65GP2yRft4ErEZLM7F1l0jb2dlw6PZGPGf5rq+iXp6mZOqXg5DVEfXIj5X2lPwaaMjl9/Qoay4uJ/fpa4Y6fbgfXTTOUUnR7CBbWz0/lfLll2HH0SusrN0wawmoRHR1aJQCDiZN/LkcKBgCbhWNO98wh/sB9B/xLtswPWeQ== x-forefront-antispam-report: CIP:255.255.255.255; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BYAPR11MB3574.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 203ebc08-2f7e-4864-03eb-08d85e28d373 X-MS-Exchange-CrossTenant-originalarrivaltime: 21 Sep 2020 12:21:11.0749 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 5ae1af62-9505-4097-a69a-c1553ef7840e X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: EGNgBxeo8d/nfhPjgw9pZlT5GKVqQGol4xw8IjoB+AFC66Ufpg5O/Mlk+6vCYucXJUE6xWZncpef1ps2K9L6Nw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR11MB3637 X-OriginatorOrg: cisco.com X-Outbound-SMTP-Client: 173.37.102.12, xch-rcd-002.cisco.com X-Outbound-Node: alln-core-5.cisco.com Subject: Re: [dpdk-dev] [PATCH] net/memif: relax barrier for zero copy path X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" > > > > > > > > Using 'rte_mb' to synchronize the shared ring head/tail between > > > > producer and consumer will stall the pipeline and damage > > > > performance on the weak memory model platforms, such like aarch64. > > > > > > > > Relax the expensive barrier with c11 atomic with explicit memory > > > > ordering can improve 3.6% performance on throughput. > > > > My question here is: `rte_mb` is supposed to make sure that head/tail > > pointer are not updated before the packets are written into shared > memory. > > Does the atomic ensures that the packets are written into shared > > memory before head/tail pointers are updated? >=20 > Yes, it does. > The atomic store-release acts as a one-way barrier here to make sure all = the > memory accesses before the store-release are observed before it. Ok then, since the sync is there and the rest seems fine to me. Thanks, Jakub Reviewed-by: Jakub Grajciar