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Received: from SJ2PR12MB8943.namprd12.prod.outlook.com (2603:10b6:a03:547::17) by IA1PR12MB6090.namprd12.prod.outlook.com (2603:10b6:208:3ee::19) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8880.31; Mon, 30 Jun 2025 14:08:00 +0000 Received: from SJ2PR12MB8943.namprd12.prod.outlook.com ([fe80::7577:f32f:798c:87cc]) by SJ2PR12MB8943.namprd12.prod.outlook.com ([fe80::7577:f32f:798c:87cc%4]) with mapi id 15.20.8880.026; Mon, 30 Jun 2025 14:08:00 +0000 From: Aurelien Aptel To: linux-nvme@lists.infradead.org, netdev@vger.kernel.org, sagi@grimberg.me, hch@lst.de, kbusch@kernel.org, axboe@fb.com, chaitanyak@nvidia.com, davem@davemloft.net, kuba@kernel.org Cc: aaptel@nvidia.com, aurelien.aptel@gmail.com, smalin@nvidia.com, malin1024@gmail.com, ogerlitz@nvidia.com, yorayz@nvidia.com, borisp@nvidia.com, galshalom@nvidia.com, mgurtovoy@nvidia.com, tariqt@nvidia.com, gus@collabora.com, viro@zeniv.linux.org.uk, akpm@linux-foundation.org Subject: [PATCH v29 03/20] iov_iter: skip copy if src == dst for direct data placement Date: Mon, 30 Jun 2025 14:07:20 +0000 Message-Id: <20250630140737.28662-4-aaptel@nvidia.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250630140737.28662-1-aaptel@nvidia.com> References: <20250630140737.28662-1-aaptel@nvidia.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: TL2P290CA0007.ISRP290.PROD.OUTLOOK.COM (2603:1096:950:2::9) To SJ2PR12MB8943.namprd12.prod.outlook.com (2603:10b6:a03:547::17) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ2PR12MB8943:EE_|IA1PR12MB6090:EE_ X-MS-Office365-Filtering-Correlation-Id: 439e7140-0722-4cc8-d4fd-08ddb7df85b0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; 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To skip copies when SKB data already resides in the destination buffer we check if (src == dst), and skip the copy when it's true. Signed-off-by: Ben Ben-Ishay Signed-off-by: Boris Pismenny Signed-off-by: Or Gerlitz Signed-off-by: Yoray Zack Signed-off-by: Shai Malin Signed-off-by: Aurelien Aptel Reviewed-by: Chaitanya Kulkarni Reviewed-by: Max Gurtovoy --- lib/iov_iter.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/lib/iov_iter.c b/lib/iov_iter.c index f9193f952f49..47fdb32653a2 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -62,7 +62,14 @@ static __always_inline size_t memcpy_to_iter(void *iter_to, size_t progress, size_t len, void *from, void *priv2) { - memcpy(iter_to, from + progress, len); + /* + * When using direct data placement (DDP) the hardware writes + * data directly to the destination buffer, and constructs + * IOVs such that they point to this data. + * Thus, when the src == dst we skip the memcpy. + */ + if (!(IS_ENABLED(CONFIG_ULP_DDP) && iter_to == from + progress)) + memcpy(iter_to, from + progress, len); return 0; } -- 2.34.1