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Received: from DS7PR12MB6069.namprd12.prod.outlook.com (2603:10b6:8:9f::13) by BN9PR12MB5034.namprd12.prod.outlook.com (2603:10b6:408:104::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6768.35; Tue, 12 Sep 2023 10:00:30 +0000 Received: from DS7PR12MB6069.namprd12.prod.outlook.com ([fe80::8ce3:c3f6:fc3a:addb]) by DS7PR12MB6069.namprd12.prod.outlook.com ([fe80::8ce3:c3f6:fc3a:addb%5]) with mapi id 15.20.6768.029; Tue, 12 Sep 2023 10:00:30 +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 v15 03/20] iov_iter: skip copy if src == dst for direct data placement Date: Tue, 12 Sep 2023 09:59:32 +0000 Message-Id: <20230912095949.5474-4-aaptel@nvidia.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230912095949.5474-1-aaptel@nvidia.com> References: <20230912095949.5474-1-aaptel@nvidia.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: FR2P281CA0055.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:93::14) To DS7PR12MB6069.namprd12.prod.outlook.com (2603:10b6:8:9f::13) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB6069:EE_|BN9PR12MB5034:EE_ X-MS-Office365-Filtering-Correlation-Id: b859a9f3-c764-42df-440d-08dbb37718d9 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 --- 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 424737045b97..5d9c8c196a39 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