From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (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 128831B4233 for ; Thu, 30 Jan 2025 21:15:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738271748; cv=none; b=MWu0vc8mmqAXyV7Pv2ogQnACnLwJU8Z5GuvlLILd2tOav7jdrtwy2o/GUgu6rVXXBNKxzoDB9tZ7iVBuIUGnaH1ui2UYRbHerz5bSDxBVP1YhsnE5xXNU/sevFkGd1R7MKNAFMtzTOBZKSDmRvOIlwBdnknBS2472QDcnecEqxs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738271748; c=relaxed/simple; bh=3u/7jLBYe2KfRcVNNTNkFn5t4vUJKiOG+tUb7ZrbBhE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=rFGRSvy8z9OrBUd3mlXTN0cMpKXK1UJ69LIgEQfBhImNQwaER1RG2IPBDdz766mpmql0nG4X2k2S6dYpPO4VJpN1jQGL3R+5UQoOGJXFFB/NyeTzlzoouoPCuiAPHYscesTN5ED3VVIcvZIQSQa0lhtx4NCX57DDawMekt/GJZw= 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=MXi2cENs; arc=none smtp.client-ip=209.85.216.74 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="MXi2cENs" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-2f81a0d0a18so2486278a91.3 for ; Thu, 30 Jan 2025 13:15:44 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1738271744; x=1738876544; darn=lists.linux.dev; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=4kMF0lC9HmaCcCSq7dy1+BxkweYLRN4mbfBRIjXSD14=; b=MXi2cENsLvyI/fp3cMJtxIpXWAQPwT/TCr5dxIs/utQGOGMszm4r8okU2OSTSKnigz IBPMNzkJ3S7vEfy1+dDr2+ZwVKnHFAQgooyZMdJzhjBiqallyt1/UvjA5gFiJOKNkzLd qhrtQ75upEk/ahjUtYVk5Td5bdTtX8HFahPUFjQjiAkafQOweoDnkBz43MLph+D+JoaD D+wuzGSrhUMOLAfXRsc6hAQDQoeWdx+bW3AQ3fO70e+jtCd8o/jote/VnoSlHujfO1zL 9ffislbONDZHCGFVFglrVIgQYuC3I2x3aQOmP4OOz9cQIyHbyerxvYDarx4Kf/2UA77K kHIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1738271744; x=1738876544; 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=4kMF0lC9HmaCcCSq7dy1+BxkweYLRN4mbfBRIjXSD14=; b=rerFk2bK5ZEB4lhgzjqoWATWTHFOXQsjX1D7qTXAoOLr1WR9L+KR4oPgAV5JKhAEhI 7Hsgzw8gscZg8+pYLtQu6OmQbnCejMsi6sU2EqTZFxJWu9Jz+yFDTnjqoeMAyO2je9yu PWgZGIHqeY2A1/YBk0Q3ZE7REQSoGiak+5z0w79mD8oMNv4jWQ5FVeJMQp3m5Jijp4lz 7zZtOv41WEWpDZXO+mDa0hcnye0LEmxwraTCQGyv3QkH+GCeaOwZ4dorzcpUIJvYTb94 Y0vfE/Wcbd0uHSDqjtguy2nrMflT5Hfvh0Cf+sHfuXpuOmCqAjAozVXFhOxenUaIfjjM dxsw== X-Forwarded-Encrypted: i=1; AJvYcCU8ENDmf6mFFXoAvHDPWQnlfHuu2sfqPFbjDQWbAe8Zp+7MVktQrcFsYhXq58LTonjgCktManb7tOgtqxsv9Q==@lists.linux.dev X-Gm-Message-State: AOJu0Yzr9LuEiitq/l7pxPHoMqPZ0idM8+srqu+StnVrYPM9CAzn/AWe CS78PoaBaBfQwyKXsOhYNjHXO/EBXUnHDENK/jsWeWZo0cMpTkKNWJPza5Qmf8pIgoEthb64Zqa F6qpXBnCadlE5dET53BD/HQ== X-Google-Smtp-Source: AGHT+IHSaYi9y/zBICOD8Bg8IwjEpl0YXsgZ0bkByw1FvqGCzDUrTuYSRphV9YF7474nI+yW7N+2oAhVQjlB0p0oJA== X-Received: from pjbsw5.prod.google.com ([2002:a17:90b:2c85:b0:2d3:d4ca:5fb0]) (user=almasrymina job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:258b:b0:2ee:fd53:2b17 with SMTP id 98e67ed59e1d1-2f83ac836d0mr12411031a91.29.1738271744350; Thu, 30 Jan 2025 13:15:44 -0800 (PST) Date: Thu, 30 Jan 2025 21:15:34 +0000 In-Reply-To: <20250130211539.428952-1-almasrymina@google.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250130211539.428952-1-almasrymina@google.com> X-Mailer: git-send-email 2.48.1.362.g079036d154-goog Message-ID: <20250130211539.428952-2-almasrymina@google.com> Subject: [PATCH RFC net-next v2 1/6] net: add devmem TCP TX documentation From: Mina Almasry To: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux.dev, linux-kselftest@vger.kernel.org Cc: Mina Almasry , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Donald Hunter , Jonathan Corbet , Andrew Lunn , David Ahern , Stefan Hajnoczi , Stefano Garzarella , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , "=?UTF-8?q?Eugenio=20P=C3=A9rez?=" , Shuah Khan , sdf@fomichev.me, asml.silence@gmail.com, dw@davidwei.uk, Jamal Hadi Salim , Victor Nogueira , Pedro Tammela Content-Type: text/plain; charset="UTF-8" Add documentation outlining the usage and details of the devmem TCP TX API. Signed-off-by: Mina Almasry --- v2: - Update documentation for iov_base is the dmabuf offset (Stan) --- Documentation/networking/devmem.rst | 144 +++++++++++++++++++++++++++- 1 file changed, 140 insertions(+), 4 deletions(-) diff --git a/Documentation/networking/devmem.rst b/Documentation/networking/devmem.rst index d95363645331..8166fe09da13 100644 --- a/Documentation/networking/devmem.rst +++ b/Documentation/networking/devmem.rst @@ -62,15 +62,15 @@ More Info https://lore.kernel.org/netdev/20240831004313.3713467-1-almasrymina@google.com/ -Interface -========= +RX Interface +============ Example ------- -tools/testing/selftests/net/ncdevmem.c:do_server shows an example of setting up -the RX path of this API. +./tools/testing/selftests/drivers/net/hw/ncdevmem:do_server shows an example of +setting up the RX path of this API. NIC Setup @@ -235,6 +235,142 @@ can be less than the tokens provided by the user in case of: (a) an internal kernel leak bug. (b) the user passed more than 1024 frags. +TX Interface +============ + + +Example +------- + +./tools/testing/selftests/drivers/net/hw/ncdevmem:do_client shows an example of +setting up the TX path of this API. + + +NIC Setup +--------- + +The user must bind a TX dmabuf to a given NIC using the netlink API:: + + struct netdev_bind_tx_req *req = NULL; + struct netdev_bind_tx_rsp *rsp = NULL; + struct ynl_error yerr; + + *ys = ynl_sock_create(&ynl_netdev_family, &yerr); + + req = netdev_bind_tx_req_alloc(); + netdev_bind_tx_req_set_ifindex(req, ifindex); + netdev_bind_tx_req_set_fd(req, dmabuf_fd); + + rsp = netdev_bind_tx(*ys, req); + + tx_dmabuf_id = rsp->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 user application must use MSG_ZEROCOPY flag when sending devmem TCP. Devmem +cannot be copied by the kernel, so the semantics of the devmem TX are similar +to the semantics of MSG_ZEROCOPY. + + ret = setsockopt(socket_fd, SOL_SOCKET, SO_ZEROCOPY, &opt, sizeof(opt)); + +Sending data +-------------- + +Devmem data is sent using the SCM_DEVMEM_DMABUF cmsg. + +The user should create a msghdr where, + +iov_base is set to the offset into the dmabuf to start sending from. +iov_len is set to the number of bytes to be sent from the dmabuf. + +The user passes the dma-buf id to send from via the dmabuf_tx_cmsg.dmabuf_id. + +The example below sends 1024 bytes from offset 100 into the dmabuf, and 2048 +from offset 2000 into the dmabuf. The dmabuf to send from is tx_dmabuf_id:: + + char ctrl_data[CMSG_SPACE(sizeof(struct dmabuf_tx_cmsg))]; + struct dmabuf_tx_cmsg ddmabuf; + struct msghdr msg = {}; + struct cmsghdr *cmsg; + struct iovec iov[2]; + + iov[0].iov_base = (void*)100; + iov[0].iov_len = 1024; + iov[1].iov_base = (void*)2000; + iov[1].iov_len = 2048; + + msg.msg_iov = iov; + msg.msg_iovlen = 2; + + msg.msg_control = ctrl_data; + msg.msg_controllen = sizeof(ctrl_data); + + cmsg = CMSG_FIRSTHDR(&msg); + cmsg->cmsg_level = SOL_SOCKET; + cmsg->cmsg_type = SCM_DEVMEM_DMABUF; + cmsg->cmsg_len = CMSG_LEN(sizeof(struct dmabuf_tx_cmsg)); + + ddmabuf.dmabuf_id = tx_dmabuf_id; + + *((struct dmabuf_tx_cmsg *)CMSG_DATA(cmsg)) = ddmabuf; + + sendmsg(socket_fd, &msg, MSG_ZEROCOPY); + + +Reusing TX dmabufs +------------------ + +Similar to MSG_ZEROCOPY with regular memory, the user should not modify the +contents of the dma-buf while a send operation is in progress. This is because +the kernel does not keep a copy of the dmabuf contents. Instead, the kernel +will pin and send data from the buffer available to the userspace. + +Just as in MSG_ZEROCOPY, the kernel notifies the userspace of send completions +using MSG_ERRQUEUE:: + + int64_t tstop = gettimeofday_ms() + waittime_ms; + char control[CMSG_SPACE(100)] = {}; + struct sock_extended_err *serr; + struct msghdr msg = {}; + struct cmsghdr *cm; + int retries = 10; + __u32 hi, lo; + + msg.msg_control = control; + msg.msg_controllen = sizeof(control); + + while (gettimeofday_ms() < tstop) { + if (!do_poll(fd)) continue; + + ret = recvmsg(fd, &msg, MSG_ERRQUEUE); + + for (cm = CMSG_FIRSTHDR(&msg); cm; cm = CMSG_NXTHDR(&msg, cm)) { + serr = (void *)CMSG_DATA(cm); + + hi = serr->ee_data; + lo = serr->ee_info; + + fprintf(stdout, "tx complete [%d,%d]\n", lo, hi); + } + } + +After the associated sendmsg has been completed, the dmabuf can be reused by +the userspace. + + Implementation & Caveats ======================== -- 2.48.1.362.g079036d154-goog