From patchwork Sun Aug 25 04:15:09 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mina Almasry X-Patchwork-Id: 13776550 Received: from mail-yb1-f201.google.com (mail-yb1-f201.google.com [209.85.219.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4E5CB7D08F for ; Sun, 25 Aug 2024 04:15:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724559352; cv=none; b=C5F9iEKA5/bPJUfVpq5m1sHG/K87Me02eJjgC2a5Gp7M7hWQC2b1J92IsYL3GBm7POQjQ/WnxrwQPn+68rzj//yFcVQKtpcMr5b5wwD3hKBOtIfVmqj6tmbBeomM02l2ZE50hiRRCybyaSHzGyHpgmPJFhoJzhvhxcdQQcHiT5o= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724559352; c=relaxed/simple; bh=tYTvD+0Km68ojLP6V9XQX/oVNkPZLntypHL7vHEaYWo=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Ct6sm45vkokvcjt5z9Ks+aNoxZ5y5F14iDokY0Dmcpk8V0NDmQCwWeoTT7kRgoKJXIGQKXUznKN0AQUFS+7GIS/6Qj8ao6Ta6yWFNZ/rlcNNcOKJLLlIEbql4sp3Z3bQ3hVdfAy3fxxrY7IcES4/OcaPBouzGUP1r3PUu1ieno0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--almasrymina.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=Fasl91CE; arc=none smtp.client-ip=209.85.219.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--almasrymina.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Fasl91CE" Received: by mail-yb1-f201.google.com with SMTP id 3f1490d57ef6-e165d8c8c28so4854747276.2 for ; Sat, 24 Aug 2024 21:15:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1724559339; x=1725164139; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=sqDPlBenPZT/vr+LnmkCTZ1L+vju9lIHvJ1xwAgpw/o=; b=Fasl91CEE4LEJ2AtT9rwAfqpwlbOGG9XxfciZZPsD+BCLrk2qV8le2q8UnhmrcYwVb lsElfZ1tmDnsFGC108wN3YUpJ5bbY9DjgMnkRTNtd3SgjCx87+UcBjZJJfglfIQ7al96 EuBY0ErSMLj2GIX0+Ckay5KeNsUqT4FyYn3WpsEKK7vvA457Ox2Brf6jOQ72YGuFZ9MI p7ffW53DVI2sF71FmnK9KJubBjflFR5bG8F/BOCDTILv98LDVfT1+75zMvzSfvDM5vHk zOcWHskMnTbt7FNG5CAfTOe2ePtS+ZJjV+96GwosbBUD/lyk80ifqCA5fD3tpfMhR7ZZ swfg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1724559339; x=1725164139; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=sqDPlBenPZT/vr+LnmkCTZ1L+vju9lIHvJ1xwAgpw/o=; b=NDVS5bFDePqmNZAYzr1VLSVFvNkJI5NZbiRzc3ty6DIYhEXVOdL2MdleVNzXH/tSfi ibwTUb38m6mF8yhaM9VqKes5IcZDpFGf4MiZOuxkIDbUiPodvrkLEskdfKDkJ8uYQbkl eXzLMq7mAeIfF9o8SyRyhTa/ptrFYBiHoOzLhr4eoKmSiL97Alem2ER20mBUNlRVNfR8 bajD4nPF4pxGWvDIHjt1e4hcAwsXxxvzVE7rkddvHDwnfNW6mAtjgRi2VJVsnRII4Pts 3lQ/7AOJ8oGoGyMMwWB6BMIEz9lCiJgaeBMj7HzJO4+rmU4QE17soFlArxfszGkIUvpx EOQQ== X-Forwarded-Encrypted: i=1; AJvYcCXA8ggyM/9sNOXGQUCwbFIbJES0Ng830/ObaOzNfksYTW5wXDQXeVskRmpcuFugrXfecRTcZ5f4bKfjeEQFaNo=@vger.kernel.org X-Gm-Message-State: AOJu0YxKMcqxRV0CEwN7baOROa6Xl2Djkwe8bGOlGUQTeJRBJYU/X5zb 11zLHG/Lr3bcrBPl96VHaqCGdPUY/C72eoSgHP+kY4DVLEQwIyVQUeVM6CYdNAlqdEgDpGp2Y4I yi9WAoiwGAH72qcV4bzYcZw== X-Google-Smtp-Source: AGHT+IFsugZHh2ZJcs9w5IfnmjiCF1dHCjWgPaLkMLCnC6ROLeLsiG8eMrJROl9guFvjFYnANH5z1PI34A47Pdo5TQ== X-Received: from almasrymina.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:4bc5]) (user=almasrymina job=sendgmr) by 2002:a25:b19f:0:b0:e05:eccb:95dc with SMTP id 3f1490d57ef6-e17a83d498fmr61841276.6.1724559339044; Sat, 24 Aug 2024 21:15:39 -0700 (PDT) Date: Sun, 25 Aug 2024 04:15:09 +0000 In-Reply-To: <20240825041511.324452-1-almasrymina@google.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240825041511.324452-1-almasrymina@google.com> X-Mailer: git-send-email 2.46.0.295.g3b9ea8a38a-goog Message-ID: <20240825041511.324452-12-almasrymina@google.com> Subject: [PATCH net-next v22 11/13] net: add devmem TCP documentation From: Mina Almasry To: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-alpha@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, sparclinux@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-arch@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org Cc: Mina Almasry , Donald Hunter , Jakub Kicinski , "David S. Miller" , Eric Dumazet , Paolo Abeni , Jonathan Corbet , Richard Henderson , Ivan Kokshaysky , Matt Turner , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Andreas Larsson , Jesper Dangaard Brouer , Ilias Apalodimas , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Arnd Bergmann , Steffen Klassert , Herbert Xu , David Ahern , Willem de Bruijn , " =?utf-8?b?QmrDtnJu?= =?utf-8?b?IFTDtnBlbA==?= " , Magnus Karlsson , Maciej Fijalkowski , Jonathan Lemon , Shuah Khan , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Sumit Semwal , " =?utf-8?q?Christian_K=C3=B6nig?= " , Pavel Begunkov , David Wei , Jason Gunthorpe , Yunsheng Lin , Shailend Chand , Harshitha Ramamurthy , Shakeel Butt , Jeroen de Borst , Praveen Kaligineedi , Bagas Sanjaya , Christoph Hellwig , Nikolay Aleksandrov , Taehee Yoo Add documentation outlining the usage and details of devmem TCP. Signed-off-by: Mina Almasry Reviewed-by: Bagas Sanjaya Reviewed-by: Donald Hunter --- v16: - Add documentation on unbinding the NIC from dmabuf (Donald). - Add note that any dmabuf should work (Donald). v9: https://lore.kernel.org/netdev/20240403002053.2376017-14-almasrymina@google.com/ - Bagas doc suggestions. v8: - Applied docs suggestions (Randy). Thanks! v7: - Applied docs suggestions (Jakub). v2: - Missing spdx (simon) - add to index.rst (simon) --- Documentation/networking/devmem.rst | 269 ++++++++++++++++++++++++++++ Documentation/networking/index.rst | 1 + 2 files changed, 270 insertions(+) create mode 100644 Documentation/networking/devmem.rst diff --git a/Documentation/networking/devmem.rst b/Documentation/networking/devmem.rst new file mode 100644 index 000000000000..417fc977844e --- /dev/null +++ b/Documentation/networking/devmem.rst @@ -0,0 +1,269 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================= +Device Memory TCP +================= + + +Intro +===== + +Device memory TCP (devmem TCP) enables receiving data directly into device +memory (dmabuf). The feature is currently implemented for TCP sockets. + + +Opportunity +----------- + +A large number of data transfers have device memory as the source and/or +destination. Accelerators drastically increased the prevalence of such +transfers. Some examples include: + +- Distributed training, where ML accelerators, such as GPUs on different hosts, + exchange data. + +- Distributed raw block storage applications transfer large amounts of data with + remote SSDs. Much of this data does not require host processing. + +Typically the Device-to-Device data transfers in the network are implemented as +the following low-level operations: Device-to-Host copy, Host-to-Host network +transfer, and Host-to-Device copy. + +The flow involving host copies is suboptimal, especially for bulk data transfers, +and can put significant strains on system resources such as host memory +bandwidth and PCIe bandwidth. + +Devmem TCP optimizes this use case by implementing socket APIs that enable +the user to receive incoming network packets directly into device memory. + +Packet payloads go directly from the NIC to device memory. + +Packet headers go to host memory and are processed by the TCP/IP stack +normally. The NIC must support header split to achieve this. + +Advantages: + +- Alleviate host memory bandwidth pressure, compared to existing + network-transfer + device-copy semantics. + +- Alleviate PCIe bandwidth pressure, by limiting data transfer to the lowest + level of the PCIe tree, compared to the traditional path which sends data + through the root complex. + + +More Info +--------- + + slides, video + https://netdevconf.org/0x17/sessions/talk/device-memory-tcp.html + + patchset + [RFC PATCH v6 00/12] Device Memory TCP + https://lore.kernel.org/netdev/20240305020153.2787423-1-almasrymina@google.com/ + + +Interface +========= + + +Example +------- + +tools/testing/selftests/net/ncdevmem.c:do_server shows an example of setting up +the RX path of this API. + + +NIC Setup +--------- + +Header split, flow steering, & RSS are required features for devmem TCP. + +Header split is used to split incoming packets into a header buffer in host +memory, and a payload buffer in device memory. + +Flow steering & RSS are used to ensure that only flows targeting devmem land on +an RX queue bound to devmem. + +Enable header split & flow steering:: + + # enable header split + ethtool -G eth1 tcp-data-split on + + + # enable flow steering + ethtool -K eth1 ntuple on + +Configure RSS to steer all traffic away from the target RX queue (queue 15 in +this example):: + + ethtool --set-rxfh-indir eth1 equal 15 + + +The user must bind a dmabuf to any number of RX queues on a given NIC using +the netlink API:: + + /* Bind dmabuf to NIC RX queue 15 */ + struct netdev_queue *queues; + queues = malloc(sizeof(*queues) * 1); + + queues[0]._present.type = 1; + queues[0]._present.idx = 1; + queues[0].type = NETDEV_RX_QUEUE_TYPE_RX; + queues[0].idx = 15; + + *ys = ynl_sock_create(&ynl_netdev_family, &yerr); + + req = netdev_bind_rx_req_alloc(); + netdev_bind_rx_req_set_ifindex(req, 1 /* ifindex */); + netdev_bind_rx_req_set_dmabuf_fd(req, dmabuf_fd); + __netdev_bind_rx_req_set_queues(req, queues, n_queue_index); + + rsp = netdev_bind_rx(*ys, req); + + dmabuf_id = rsp->dmabuf_id; + + +The netlink API returns a dmabuf_id: a unique ID that refers to this dmabuf +that has been bound. + +The user can unbind the dmabuf from the netdevice by closing the netlink socket +that established the binding. We do this so that the binding is automatically +unbound even if the userspace process crashes. + +Note that any reasonably well-behaved dmabuf from any exporter should work with +devmem TCP, even if the dmabuf is not actually backed by devmem. An example of +this is udmabuf, which wraps user memory (non-devmem) in a dmabuf. + + +Socket Setup +------------ + +The socket must be flow steered to the dmabuf bound RX queue:: + + ethtool -N eth1 flow-type tcp4 ... queue 15, + + +Receiving data +-------------- + +The user application must signal to the kernel that it is capable of receiving +devmem data by passing the MSG_SOCK_DEVMEM flag to recvmsg:: + + ret = recvmsg(fd, &msg, MSG_SOCK_DEVMEM); + +Applications that do not specify the MSG_SOCK_DEVMEM flag will receive an EFAULT +on devmem data. + +Devmem data is received directly into the dmabuf bound to the NIC in 'NIC +Setup', and the kernel signals such to the user via the SCM_DEVMEM_* cmsgs:: + + for (cm = CMSG_FIRSTHDR(&msg); cm; cm = CMSG_NXTHDR(&msg, cm)) { + if (cm->cmsg_level != SOL_SOCKET || + (cm->cmsg_type != SCM_DEVMEM_DMABUF && + cm->cmsg_type != SCM_DEVMEM_LINEAR)) + continue; + + dmabuf_cmsg = (struct dmabuf_cmsg *)CMSG_DATA(cm); + + if (cm->cmsg_type == SCM_DEVMEM_DMABUF) { + /* Frag landed in dmabuf. + * + * dmabuf_cmsg->dmabuf_id is the dmabuf the + * frag landed on. + * + * dmabuf_cmsg->frag_offset is the offset into + * the dmabuf where the frag starts. + * + * dmabuf_cmsg->frag_size is the size of the + * frag. + * + * dmabuf_cmsg->frag_token is a token used to + * refer to this frag for later freeing. + */ + + struct dmabuf_token token; + token.token_start = dmabuf_cmsg->frag_token; + token.token_count = 1; + continue; + } + + if (cm->cmsg_type == SCM_DEVMEM_LINEAR) + /* Frag landed in linear buffer. + * + * dmabuf_cmsg->frag_size is the size of the + * frag. + */ + continue; + + } + +Applications may receive 2 cmsgs: + +- SCM_DEVMEM_DMABUF: this indicates the fragment landed in the dmabuf indicated + by dmabuf_id. + +- SCM_DEVMEM_LINEAR: this indicates the fragment landed in the linear buffer. + This typically happens when the NIC is unable to split the packet at the + header boundary, such that part (or all) of the payload landed in host + memory. + +Applications may receive no SO_DEVMEM_* cmsgs. That indicates non-devmem, +regular TCP data that landed on an RX queue not bound to a dmabuf. + + +Freeing frags +------------- + +Frags received via SCM_DEVMEM_DMABUF are pinned by the kernel while the user +processes the frag. The user must return the frag to the kernel via +SO_DEVMEM_DONTNEED:: + + ret = setsockopt(client_fd, SOL_SOCKET, SO_DEVMEM_DONTNEED, &token, + sizeof(token)); + +The user must ensure the tokens are returned to the kernel in a timely manner. +Failure to do so will exhaust the limited dmabuf that is bound to the RX queue +and will lead to packet drops. + + +Implementation & Caveats +======================== + +Unreadable skbs +--------------- + +Devmem payloads are inaccessible to the kernel processing the packets. This +results in a few quirks for payloads of devmem skbs: + +- Loopback is not functional. Loopback relies on copying the payload, which is + not possible with devmem skbs. + +- Software checksum calculation fails. + +- TCP Dump and bpf can't access devmem packet payloads. + + +Testing +======= + +More realistic example code can be found in the kernel source under +tools/testing/selftests/net/ncdevmem.c + +ncdevmem is a devmem TCP netcat. It works very similarly to netcat, but +receives data directly into a udmabuf. + +To run ncdevmem, you need to run it on a server on the machine under test, and +you need to run netcat on a peer to provide the TX data. + +ncdevmem has a validation mode as well that expects a repeating pattern of +incoming data and validates it as such. For example, you can launch +ncdevmem on the server by:: + + ncdevmem -s -c -f eth1 -d 3 -n 0000:06:00.0 -l \ + -p 5201 -v 7 + +On client side, use regular netcat to send TX data to ncdevmem process +on the server:: + + yes $(echo -e \\x01\\x02\\x03\\x04\\x05\\x06) | \ + tr \\n \\0 | head -c 5G | nc 5201 -p 5201 diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst index c71b87346178..08f437c326ab 100644 --- a/Documentation/networking/index.rst +++ b/Documentation/networking/index.rst @@ -49,6 +49,7 @@ Contents: cdc_mbim dccp dctcp + devmem dns_resolver driver eql