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Tue, 18 May 2021 12:13:05 +0000 From: Slava Ovsiienko To: Feifei Wang , Matan Azrad , Shahaf Shuler CC: "dev@dpdk.org" , "nd@arm.com" , Ruifeng Wang Thread-Topic: [dpdk-dev] [PATCH v3 1/2] net/mlx4: remove unnecessary wmb for Memory Region cache Thread-Index: AQHXS8L3UpoazGpHhEy31KvKW5pBRqrpJqAA Date: Tue, 18 May 2021 12:13:05 +0000 Message-ID: References: <20210318071840.359957-1-feifei.wang2@arm.com> <20210518085058.630072-1-feifei.wang2@arm.com> <20210518085058.630072-2-feifei.wang2@arm.com> In-Reply-To: <20210518085058.630072-2-feifei.wang2@arm.com> 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=nvidia.com; x-originating-ip: [188.163.75.124] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: f8b354ef-cf0b-4c77-253b-08d919f64aa7 x-ms-traffictypediagnostic: DM6PR12MB4121: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:4303; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: DM6PR12MB3753.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: f8b354ef-cf0b-4c77-253b-08d919f64aa7 X-MS-Exchange-CrossTenant-originalarrivaltime: 18 May 2021 12:13:05.3403 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: bDGXGvYpEIkFFW07/GAMkCZ/rZLw7pWYHz1HEKgqxH8bx7UcRAIvTYfNngT5mutDZmC9ae/kv3GMrXjjIMfy7w== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4121 Subject: Re: [dpdk-dev] [PATCH v3 1/2] net/mlx4: remove unnecessary wmb for Memory Region cache X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 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" > -----Original Message----- > From: dev On Behalf Of Feifei Wang > Sent: Tuesday, May 18, 2021 11:51 > To: Matan Azrad ; Shahaf Shuler > > Cc: dev@dpdk.org; nd@arm.com; Feifei Wang ; > Ruifeng Wang > Subject: [dpdk-dev] [PATCH v3 1/2] net/mlx4: remove unnecessary wmb for > Memory Region cache >=20 > 'dev_gen' is a variable to trigger all cores to flush their local caches = once the > global MR cache has been rebuilt. >=20 > This is due to MR cache's R/W lock can maintain synchronization between > threads: >=20 > 1. dev_gen and global cache updating ordering inside the lock protected > section does not matter. Because other threads cannot take the lock until > global cache has been updated. Thus, in out of order platform, even if ot= her > agents firstly observe updated dev_gen but global does not update, they s= till > have to wait the lock. As a result, it is unnecessary to add a wmb betwee= n > global cache rebuilding and updating the dev_gen to keep the memory store > order. >=20 > 2. Store-Release of unlock provides the implicit wmb at the level visible= by > software. This makes 'rebuilding global cache' and 'updating dev_gen' be > observed before local_cache starts to be updated by other agents. Thus, > wmb after 'updating dev_gen' can be removed. >=20 > Suggested-by: Ruifeng Wang > Signed-off-by: Feifei Wang > Reviewed-by: Ruifeng Wang Acked-by: Viacheslav Ovsiienko