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[84.110.32.226]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-35f048dddddsm8554380f8f.111.2024.06.10.07.30.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 10 Jun 2024 07:30:35 -0700 (PDT) Message-ID: <9a03d3bf-c48f-4758-9d7f-a5e7920ec68f@grimberg.me> Date: Mon, 10 Jun 2024 17:30:34 +0300 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v25 00/20] nvme-tcp receive offloads To: Christoph Hellwig Cc: Jakub Kicinski , Aurelien Aptel , linux-nvme@lists.infradead.org, netdev@vger.kernel.org, kbusch@kernel.org, axboe@fb.com, chaitanyak@nvidia.com, davem@davemloft.net References: <20240529160053.111531-1-aaptel@nvidia.com> <20240530183906.4534c029@kernel.org> <20240531061142.GB17723@lst.de> <06d9c3c9-8d27-46bf-a0cf-0c3ea1a0d3ec@grimberg.me> <20240610122939.GA21899@lst.de> Content-Language: en-US From: Sagi Grimberg In-Reply-To: <20240610122939.GA21899@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/06/2024 15:29, Christoph Hellwig wrote: > On Mon, Jun 03, 2024 at 10:09:26AM +0300, Sagi Grimberg wrote: >>> IETF has standardized a generic data placement protocol, which is >>> part of iWarp. Even if folks don't like RDMA it exists to solve >>> exactly these kinds of problems of data placement. >> iWARP changes the wire protocol. > Compared to plain NVMe over TCP that's a bit of an understatement :) Yes :) the comment was that people want to use NVMe/TCP, and adding DDP awareness inspired by iWARP would change the existing NVMe/TCP wire protocol. This offload, does not. > >> Is your comment to just go make people >> use iWARP instead of TCP? or extending NVMe/TCP to natively support DDP? > I don't know to be honest. In many ways just using RDMA instead of > NVMe/TCP would solve all the problems this is trying to solve, but > there are enough big customers that have religious concerns about > the use of RDMA. > > So if people want to use something that looks non-RDMA but have the > same benefits we have to reinvent it quite similarly under a different > name. Looking at DDP and what we can learn from it without bringing > the Verbs API along might be one way to do that. > > Another would be to figure out what amount of similarity and what > amount of state we need in an on the wire protocol to have an > efficient header splitting in the NIC, either hard coded or even > better downloadable using something like eBPF. From what I understand, this is what this offload is trying to do. It uses the nvme command_id similar to how the read_stag is used in iwarp, it tracks the NVMe/TCP pdus to split pdus from data transfers, and maps the command_id to an internal MR for dma purposes. What I think you don't like about this is the interface that the offload exposes to the TCP ulp driver (nvme-tcp in our case)? > >> That would be great, but what does a "vendor independent without hooks" >> look like from >> your perspective? I'd love having this translate to standard (and some new) >> socket operations, >> but I could not find a way that this can be done given the current >> architecture. > Any amount of calls into NIC/offload drivers from NVMe is a nogo. > Not following you here... *something* needs to program a buffer for DDP, *something* needs to invalidate this buffer, *something* needs to declare a TCP stream as DDP capable. Unless I interpret what you're saying is that the interface needs to be generalized to extend the standard socket operations (i.e. [s|g]etsockopt/recvmsg/cmsghdr etc) ?