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Received: from SJ1PR12MB6075.namprd12.prod.outlook.com (2603:10b6:a03:45e::8) by IA1PR12MB6259.namprd12.prod.outlook.com (2603:10b6:208:3e5::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6907.26; Tue, 24 Oct 2023 12:55:16 +0000 Received: from SJ1PR12MB6075.namprd12.prod.outlook.com ([fe80::42b4:7f1:b049:39b2]) by SJ1PR12MB6075.namprd12.prod.outlook.com ([fe80::42b4:7f1:b049:39b2%6]) with mapi id 15.20.6907.030; Tue, 24 Oct 2023 12:55:16 +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: Ben Ben-Ishay , 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 v17 03/20] iov_iter: skip copy if src == dst for direct data placement Date: Tue, 24 Oct 2023 12:54:28 +0000 Message-Id: <20231024125445.2632-4-aaptel@nvidia.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231024125445.2632-1-aaptel@nvidia.com> References: <20231024125445.2632-1-aaptel@nvidia.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: LNXP265CA0065.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:5d::29) To SJ1PR12MB6075.namprd12.prod.outlook.com (2603:10b6:a03:45e::8) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PR12MB6075:EE_|IA1PR12MB6259:EE_ X-MS-Office365-Filtering-Correlation-Id: 77ad6d17-801d-490d-ceb5-08dbd490784f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org From: Ben Ben-Ishay When using direct data placement (DDP) the NIC could write the payload directly into the destination buffer and constructs SKBs such that they point to this data. 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 --- lib/iov_iter.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 27234a820eeb..279b2c5b1936 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -313,9 +313,15 @@ size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i) return 0; if (user_backed_iter(i)) might_fault(); + /* + * 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. + */ iterate_and_advance(i, bytes, base, len, off, copyout(base, addr + off, len), - memcpy(base, addr + off, len) + (base != addr + off) && memcpy(base, addr + off, len) ) return bytes; -- 2.34.1