From patchwork Thu Feb 20 02:09:10 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mina Almasry X-Patchwork-Id: 13983208 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (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 03AA91DC991 for ; Thu, 20 Feb 2025 02:09:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740017372; cv=none; b=Ahpzth683MP7/qlOSwk383H+yRXc+fNb2ictOu4ZEbpdWL02E5+hHZSnLYcNo+vqaCQ6Qo1I1PMiz/6vqQ5H1YiC12l/9jwB/SnpDkOeMm7QgKrW82pOLN3IQqu8zuvS58H1lPTH0SC8wXzraMMSNIHSBCcUs5c2fo8bufI6UBg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740017372; c=relaxed/simple; bh=q5XsmN0+qNQcTTcfaJ4MRPPi7x8kiGcH8m4E8CxyZWo=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=FWJ0Dd/HCu0FcxukMYMIP9tcB5ZHRSUWHJ6VLiidMFQY9JMgchxm+vQA+tapJ/5Jc6lvJQZRjAmkUol3/ikIwPI/hXwsp5gYXuzfmqSAoM0VpFmFL5SxSWeLaTIKuJNfm61+n65LyAlIuDSAFjTArF7h+1/w0jmcv9Wjg0MRLGI= 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=H+Pe0RO9; arc=none smtp.client-ip=209.85.214.201 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="H+Pe0RO9" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-220ec5c16e9so11024355ad.1 for ; Wed, 19 Feb 2025 18:09:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1740017369; x=1740622169; 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=9i5ITI5hsYXNkk95ANyYz00PWaNA3wxaXmmfqorxWmI=; b=H+Pe0RO9SXEt2yoQXi3IeYHdYopwcJsr3ByJ3xKi76c/eFSovzJjpsO4Jbi1l+BInl b4nPPck/EI3cCo7HQ88Ml8niXEWjoS9t1WABh7EITKGnTXJqAXiVDB89KY+hX+MVZ9Ar yxp37z+l9hLOlSv547GKIftyWeXfX28IcZ2jiPb51Sn6tVuUQN/ptV8ZeRdogPJiH4E0 brkEGnaR/+ZFejIfxhUP/F9yCms9UxPXVqECTovw75kbwo6b82hGFfT6S+T8YIXP7J3p 6LSFkVERGgLEo4Srk8QkCoPVAVk64Nd0/dAiTCnnlDXn75zk2nafzunnkGMOQwX+AmQm 05+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740017369; x=1740622169; 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=9i5ITI5hsYXNkk95ANyYz00PWaNA3wxaXmmfqorxWmI=; b=baWz7uxaGNQDwCtC11IWo3UYug4NDgg6vl22VXMe7E/nBCtEmOKo3tmKCFYJBoCTl1 dOctzx1eYJadtMo3I/U7utKxZm1Xr797XEEVKcFZLe/CJmcccHFxgglzxNORkSJbhbkj RzNpvo2abCpcOUGDJEnFV4u3yVQZf1n/BXOswr0+nlCzfpJkIDWXZio2yJ5IjMHGZdNG /61wNZVaQ5jRV4g7eHERy7imB/uVBqB9Xt8s5E0wxDRVlbdM9M0WvENgIW3d4dKZfxpB BDjuTz4FYak2KV6vgsOp/vJYTOjyaxUnoiVNYZZAp8o3Is7qTlTZdZGLt8DXSjJvTT6U W4yA== X-Forwarded-Encrypted: i=1; AJvYcCUBkrP8KQKCi2ZiSIYNRWrI6/MjHiU+rCaEMCcPn0DPb/2JIX/iKCC58SJlZ7HI+E/BY4NFqcxMDbiQmAwM1EI=@vger.kernel.org X-Gm-Message-State: AOJu0Yw3mEUdU4pPY1jdGvNsm1uUJRRNaUW/dauNzOVv6/m+/DUhR2VF bjv6SyMf+g8KjyEvpsO0xFCYwlq24+rA2as8NQwHM6G5jnd5r2o2gsqr8nhWOs4KW0f+Sjfz8hs I0kNfaA2oltCKv+o4csZkPQ== X-Google-Smtp-Source: AGHT+IFWUpLngVjg4ZRvdMcFQlYPunbjfg+CrCWS1N/fYD0oezyFMNiTwHerTLo6whLbQg+u/NAp0xpJYUvUoObtoQ== X-Received: from plqw12.prod.google.com ([2002:a17:902:a70c:b0:21f:4d14:8384]) (user=almasrymina job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:e54e:b0:220:ff3f:6cc5 with SMTP id d9443c01a7336-221040bf806mr344999995ad.35.1740017369127; Wed, 19 Feb 2025 18:09:29 -0800 (PST) Date: Thu, 20 Feb 2025 02:09:10 +0000 In-Reply-To: <20250220020914.895431-1-almasrymina@google.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250220020914.895431-1-almasrymina@google.com> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog Message-ID: <20250220020914.895431-6-almasrymina@google.com> Subject: [PATCH net-next v4 5/9] net: add devmem TCP TX documentation From: Mina Almasry To: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org, 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 , Jeroen de Borst , Praveen Kaligineedi , Shailend Chand , Kuniyuki Iwashima , Willem de Bruijn , David Ahern , Neal Cardwell , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , " =?utf-8?q?Eugenio_P=C3=A9rez?= " , Stefan Hajnoczi , Stefano Garzarella , Shuah Khan , sdf@fomichev.me, asml.silence@gmail.com, dw@davidwei.uk, Jamal Hadi Salim , Victor Nogueira , Pedro Tammela , Samiullah Khawaja Add documentation outlining the usage and details of the devmem TCP TX API. Signed-off-by: Mina Almasry Acked-by: Stanislav Fomichev --- v4: - Mention SO_BINDTODEVICE is recommended (me/Pavel). v2: - Update documentation for iov_base is the dmabuf offset (Stan) --- Documentation/networking/devmem.rst | 150 +++++++++++++++++++++++++++- 1 file changed, 146 insertions(+), 4 deletions(-) diff --git a/Documentation/networking/devmem.rst b/Documentation/networking/devmem.rst index d95363645331..10928a5f912f 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 +235,148 @@ 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. + + setsockopt(socket_fd, SOL_SOCKET, SO_ZEROCOPY, &opt, sizeof(opt)); + +It is also recommended that the user binds the TX socket to the same interface +the dma-buf has been bound to via SO_BINDTODEVICE. + + setsockopt(socket_fd, SOL_SOCKET, SO_BINDTODEVICE, ifname, strlen(ifname) + 1); + + +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 ========================