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Thu, 4 Apr 2024 12:37:41 +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, viro@zeniv.linux.org.uk Subject: [PATCH v24 03/20] iov_iter: skip copy if src == dst for direct data placement Date: Thu, 4 Apr 2024 12:37:00 +0000 Message-Id: <20240404123717.11857-4-aaptel@nvidia.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240404123717.11857-1-aaptel@nvidia.com> References: <20240404123717.11857-1-aaptel@nvidia.com> X-ClientProxiedBy: FR0P281CA0134.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:97::18) To SJ1PR12MB6075.namprd12.prod.outlook.com (2603:10b6:a03:45e::8) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PR12MB6075:EE_|SA1PR12MB7104:EE_ X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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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 4a6a9f419bd7..a85125485174 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 (iter_to != from + progress) + memcpy(iter_to, from + progress, len); return 0; }