From patchwork Tue Mar 5 02:01:49 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mina Almasry X-Patchwork-Id: 13581465 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (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 36F7A7E797 for ; Tue, 5 Mar 2024 02:02:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709604154; cv=none; b=kgAY5HEdt/2T5GxmkMEGstSsaafj217ALdWuYsDJG3LyxzO5qrx3rFwnNI4nTA4UTVVN2joMQwDTChVHzDkplfdmFcsZG2JH2TYgw2/5vGQ5DPlwco36uvJL6QiBt6ulirPO43ODdNvu9ug8JWh/+i5U2A2lxefWgi8q09V2MMQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709604154; c=relaxed/simple; bh=pfSBox9Ga0DV9HP7LL34Jt5xxP+j2xIrHHM73+n+DHw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=tml4KnULrZDMy3O7PngPI2Jwa2vAGl8mqTNqWNkVmFmiHApPquQW6dU6+9y3lqzY944dkF6+H4RWqg8TZTMXmWp8vAnHPq5CGlq4rT+Qfx/DvsKWB7zQWJa4FS0tVqIfY8ppEH52/BF003US/tra4UckyvYhmBDsq8chaevtKtY= 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=kbYkxrnX; arc=none smtp.client-ip=209.85.128.201 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="kbYkxrnX" Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-5f38d676cecso80458037b3.0 for ; Mon, 04 Mar 2024 18:02:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1709604147; x=1710208947; 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=cdaLgPgB3k0IUnbuFiSyW7eJOw/whsgAOWZdbzevfeI=; b=kbYkxrnXAOt9lB6I0LQo4/KBekOwEsHRtYE1sMrEEQbtr7ohxPkZcWhCxivuttc97/ tkoH8e3F0KolYpoL/IrfDDTxEs8vWXCswalyEjF4H+v8ZBWWwOgnWer9ecwNPURaI8fP DX1u/GmTr/iXpA2c+bUlDT85sOMon55Q4F62J69qmSY4cI4mT7lJRmvQkg6RiLogtgDH U27Vk+at9Ayci3qiW62ME3aIo3C+VnQA3aC2wc7c1bTJYq/K6WaPkFFay1bzAzHxk00L 83IGr+vYvyh5WW9XqBoZyzQcbwZsM389I8V33vZdf9UEeW/yO9hQyTGl9lUbNiPI7xA5 fBLw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1709604147; x=1710208947; 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=cdaLgPgB3k0IUnbuFiSyW7eJOw/whsgAOWZdbzevfeI=; b=Bv5rYULsN9zV5Q2IPAWX5pyinHEkFK4fk3DM2+kTZkm+E35Rkbitbfl8/7PnmsSs/9 zfUovFL+K7ptewnZS2VmTzCwu7cBt6H9/caVSbENqXb8uUvdxGcl/BzOylXm3PqQCmd7 SIvJHRWTJQp4b37KLFRurY5jiGY+pemnm+UuisgI6j9F5Y7/2kwhC0fY2a4p4eH9BjtR 3YgqvozQlc8eAdQ/35evv3hR41t1SGeVC2deOMVtOrQ6omkvHIfPTN1IikFR755LnDXO lWKz6cvKdUaxpQD8SaNWLbs2y2xslXMkiiZGbyEAT+ay+AyKa+58D3pV8DteOhDn4v3a ZSZA== X-Forwarded-Encrypted: i=1; AJvYcCUoxCmopVGvUWknfJ5gQIcwtX/f4DRwzrmVhwmdX5/IxfKcPWkzgSy1lqH/qTLKr417fyCC1L+XCoEv0NNmos//pV0U5hxZAmhogA== X-Gm-Message-State: AOJu0YwnQWfcBQAtMrkpe67sOfOlLWQ5d4tQseP3L5v8sAUrTqeldPoI LEpw9JGeU7Mj3bIdb6d0Y+AncKK1lkImSoiKAsQK5ZV8nMZBTOKT/nbMbALBSE+cRiNZ6cQ4YCe 4FrON1Mt6pyaRHmk87hctww== X-Google-Smtp-Source: AGHT+IHQs0SIwa2ekbs3tLJ18U+t6mqdEQQQa57loe9W+ctuY8OVB4RpI+mzdPMB5Lnn+KZ21aUA8Q2c99dGnxQY1A== X-Received: from almasrymina.svl.corp.google.com ([2620:15c:2c4:200:b614:914c:63cd:3830]) (user=almasrymina job=sendgmr) by 2002:a5b:54c:0:b0:dc7:5925:92d2 with SMTP id r12-20020a5b054c000000b00dc7592592d2mr249722ybp.1.1709604147667; Mon, 04 Mar 2024 18:02:27 -0800 (PST) Date: Mon, 4 Mar 2024 18:01:49 -0800 In-Reply-To: <20240305020153.2787423-1-almasrymina@google.com> Precedence: bulk X-Mailing-List: linux-mips@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240305020153.2787423-1-almasrymina@google.com> X-Mailer: git-send-email 2.44.0.rc1.240.g4c46232300-goog Message-ID: <20240305020153.2787423-15-almasrymina@google.com> Subject: [RFC PATCH net-next v6 14/15] 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 , "David S. Miller" , Eric Dumazet , Jakub Kicinski , 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 , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , David Ahern , Willem de Bruijn , Shuah Khan , 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 Signed-off-by: Mina Almasry --- v1 -> v2: - Missing spdx (simon) - add to index.rst (simon) --- Documentation/networking/devmem.rst | 271 ++++++++++++++++++++++++++++ Documentation/networking/index.rst | 1 + 2 files changed, 272 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..4712f029e5ed --- /dev/null +++ b/Documentation/networking/devmem.rst @@ -0,0 +1,271 @@ +.. 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 amount of data transfers have device memory as the source and/or +destination. Accelerators drastically increased the volume of such transfers. +Some examples include: + +- Distributed training, where ML accelerators, such as GPUs on different hosts, + exchange data among them. + +- Distributed raw block storage applications transfer large amounts of data with + remote SSDs, much of this data does not require host processing. + +Today, the majority of the Device-to-Device data transfers 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 implementation 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 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 v3 00/12] Device Memory TCP + https://lore.kernel.org/lkml/20231106024413.2801438-1-almasrymina@google.com/T/ + + +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 +RX queue bound to devmem. + +Enable header split & flow steering: + +:: + + # enable header split (assuming priv-flag) + ethtool --set-priv-flags eth1 enable-header-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 +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. + +Socket Setup +------------ + +The socket must be flow steering 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 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: + +:: + + # On server: + ncdevmem -s -c -f eth1 -d 3 -n 0000:06:00.0 -l \ + -p 5201 -v 7 + + # On client: + 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 69f3d6dcd9fd..d9f86514aa1e 100644 --- a/Documentation/networking/index.rst +++ b/Documentation/networking/index.rst @@ -48,6 +48,7 @@ Contents: cdc_mbim dccp dctcp + devmem dns_resolver driver eql