From patchwork Wed Feb 12 18:58:00 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Wei X-Patchwork-Id: 13972321 Received: from mail-pl1-f171.google.com (mail-pl1-f171.google.com [209.85.214.171]) (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 6B87C262817 for ; Wed, 12 Feb 2025 18:59:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.171 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739386760; cv=none; b=hs8lwOsKb+vwOPG+ZXXARGYCnG709JkcVa9dnAn5Jxxsi+5nx66hMQbMOhxjp9blJaG33MPUlZF31dkCQH8fLzCRKHHymZRWaWsxfSgSEaZiOaiTHRbewNBD4H3CuJKNCYwplZLHL+CKEjq/D35JIozz/PtWxImieYWOZv9bRtU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739386760; c=relaxed/simple; bh=9pTdmByBVpWL3oRo72V1P/Qnfm3p1w1EAQ8TvZwzW4E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=pesTNugIFGUoxuK9MbdjpIYjaOO4UIEdJImTVm0DyrDjbe7LYNwwfKH7P4j7WkC3MTuG4Rt7NcOjgEgqt9rL9CnhWsoKYLsrWJtKWhC7DAgLAs9ORBxHBaQQE3UpHYU0kiA5H7FB6JEX0RLnFJ0jYA2PX52TCIp6AT+a9b6h2E4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=davidwei.uk; spf=none smtp.mailfrom=davidwei.uk; dkim=pass (2048-bit key) header.d=davidwei-uk.20230601.gappssmtp.com header.i=@davidwei-uk.20230601.gappssmtp.com header.b=EmbZ8TjM; arc=none smtp.client-ip=209.85.214.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=davidwei.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=davidwei.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=davidwei-uk.20230601.gappssmtp.com header.i=@davidwei-uk.20230601.gappssmtp.com header.b="EmbZ8TjM" Received: by mail-pl1-f171.google.com with SMTP id d9443c01a7336-220c8f38febso14439925ad.2 for ; Wed, 12 Feb 2025 10:59:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=davidwei-uk.20230601.gappssmtp.com; s=20230601; t=1739386756; x=1739991556; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=NHWoGsRhiFc/ooKo3TvF3R3d8ADOTW+DffRpnDLhJ48=; b=EmbZ8TjMTdDrfcM+n2gNijV42NI28HDG6dgezndFymBVQOffsQgEGvR/VobYIOtV/z 0fPdqzePGwTnA5hav5gIwAcU2gbDgXbuQ8jjoMggRFzDJnKbpTJ1XOeU1WjwidZhSlvu /YT7yHqaEeh3e2hLq4RQirH4D/1xZEXgjO140KDdsKP/xQh7SLm/uFrTjsUH6FibYPec YogppvISJX1K+Ipt7BTtn21yVnc7EIcz16OtzeZc5jlQLsvLhIv2k6gS1YByp+CEnnXX SX/76WjQ8VR3nv0B6EuYlKX9VmEoJkcRX2H+w0X7SBkUsvvH9Om6MPbQaB7Zq6lJKqGT 2swg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739386756; x=1739991556; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=NHWoGsRhiFc/ooKo3TvF3R3d8ADOTW+DffRpnDLhJ48=; b=K2hPrMgxfoW6dSMHZzrILq60zOZkABv6UxG6rMGaBUGKPuTQXIgBAKa4JGXyQ7Kq7K Jrygz1Q4BvgDcDy8X/18tQGed1njqjl1AsayuVZ42gFRyWKOKgmm4lNNxG/A9TPaBXzk lW+sjkaMhRNkxwsBsgxfrKB5/Ijfzivsl2Na8+88ZFnt55eGEEsbYPM6dOZf9NDLqfoq rXN/dJZQ4QuiHHF1fYnXSjopVbvLAJxKoM4GrfP62FLs+YY1t392SiYKLeGlWWdIRvfT E8mVXxzJykWoxCkgFlFrjz8KsnnrL4YnG1LA1HCG0fojz21Zn70zmOSSyWCnuYCQdx2I IT4w== X-Gm-Message-State: AOJu0YwtEfjN2QPPmbjpiXkb38p8mvT7E/w0Q6Zb5ZcR8da3zqHZtVfU gbdH2R79jFb4qj/mFtjbioC4A744P4YoLntiAifnxrsuUPNbITDfj6XJMLuxvkMJA5f5gB8yc7b V X-Gm-Gg: ASbGncvthEd+04Viq1rhjpGYthJfI11sE0A9sLdoQ3frONJ1XU2TBkdNiSollA94nVK bkRX74Ug23uszEfCNW40K2cv3Fd00wHAsCBZ8nvFbt7s5/xUH7xYva0baknXjprJ/uH39I4khIf SO1dXlTWc00Nu0PMKVZ+X6zYKpHdXPTxBPKH7Cf98PL4ILaGyPm5yYCa85QHzhG3Qzq8aK57J0Y UMhE8myFAhxpi5C5CalWBDkNZ5VoFL463B0E7PKKQfWBUU1tfH+Iy59hIaRVRjyfeo5x8toUpwB X-Google-Smtp-Source: AGHT+IHCFlfixa6KjP6YmcpUGIN/NNsejdfcLQhFihNNDU8POVbfi8RxA+ESXd2uIhuEC5K8YngjiQ== X-Received: by 2002:a05:6a21:6da8:b0:1e1:cbbf:be0 with SMTP id adf61e73a8af0-1ee5e5bbea4mr7406758637.22.1739386755760; Wed, 12 Feb 2025 10:59:15 -0800 (PST) Received: from localhost ([2a03:2880:ff:71::]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7307a29ecdesm8003949b3a.173.2025.02.12.10.59.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Feb 2025 10:59:15 -0800 (PST) From: David Wei To: io-uring@vger.kernel.org, netdev@vger.kernel.org Cc: Jens Axboe , Pavel Begunkov , Jakub Kicinski , Paolo Abeni , "David S. Miller" , Eric Dumazet , Jesper Dangaard Brouer , David Ahern , Mina Almasry , Stanislav Fomichev , Joe Damato , Pedro Tammela Subject: [PATCH net-next v13 10/11] net: add documentation for io_uring zcrx Date: Wed, 12 Feb 2025 10:58:00 -0800 Message-ID: <20250212185859.3509616-11-dw@davidwei.uk> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20250212185859.3509616-1-dw@davidwei.uk> References: <20250212185859.3509616-1-dw@davidwei.uk> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Add documentation for io_uring zero copy Rx that explains requirements and the user API. Signed-off-by: David Wei --- Documentation/networking/index.rst | 1 + Documentation/networking/iou-zcrx.rst | 202 ++++++++++++++++++++++++++ 2 files changed, 203 insertions(+) create mode 100644 Documentation/networking/iou-zcrx.rst diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst index 058193ed2eeb..c64133d309bf 100644 --- a/Documentation/networking/index.rst +++ b/Documentation/networking/index.rst @@ -63,6 +63,7 @@ Contents: gtp ila ioam6-sysctl + iou-zcrx ip_dynaddr ipsec ip-sysctl diff --git a/Documentation/networking/iou-zcrx.rst b/Documentation/networking/iou-zcrx.rst new file mode 100644 index 000000000000..0127319b30bb --- /dev/null +++ b/Documentation/networking/iou-zcrx.rst @@ -0,0 +1,202 @@ +.. SPDX-License-Identifier: GPL-2.0 + +===================== +io_uring zero copy Rx +===================== + +Introduction +============ + +io_uring zero copy Rx (ZC Rx) is a feature that removes kernel-to-user copy on +the network receive path, allowing packet data to be received directly into +userspace memory. This feature is different to TCP_ZEROCOPY_RECEIVE in that +there are no strict alignment requirements and no need to mmap()/munmap(). +Compared to kernel bypass solutions such as e.g. DPDK, the packet headers are +processed by the kernel TCP stack as normal. + +NIC HW Requirements +=================== + +Several NIC HW features are required for io_uring ZC Rx to work. For now the +kernel API does not configure the NIC and it must be done by the user. + +Header/data split +----------------- + +Required to split packets at the L4 boundary into a header and a payload. +Headers are received into kernel memory as normal and processed by the TCP +stack as normal. Payloads are received into userspace memory directly. + +Flow steering +------------- + +Specific HW Rx queues are configured for this feature, but modern NICs +typically distribute flows across all HW Rx queues. Flow steering is required +to ensure that only desired flows are directed towards HW queues that are +configured for io_uring ZC Rx. + +RSS +--- + +In addition to flow steering above, RSS is required to steer all other non-zero +copy flows away from queues that are configured for io_uring ZC Rx. + +Usage +===== + +Setup NIC +--------- + +Must be done out of band for now. + +Ensure there are at least two queues:: + + ethtool -L eth0 combined 2 + +Enable header/data split:: + + ethtool -G eth0 tcp-data-split on + +Carve out half of the HW Rx queues for zero copy using RSS:: + + ethtool -X eth0 equal 1 + +Set up flow steering, bearing in mind that queues are 0-indexed:: + + ethtool -N eth0 flow-type tcp6 ... action 1 + +Setup io_uring +-------------- + +This section describes the low level io_uring kernel API. Please refer to +liburing documentation for how to use the higher level API. + +Create an io_uring instance with the following required setup flags:: + + IORING_SETUP_SINGLE_ISSUER + IORING_SETUP_DEFER_TASKRUN + IORING_SETUP_CQE32 + +Create memory area +------------------ + +Allocate userspace memory area for receiving zero copy data:: + + void *area_ptr = mmap(NULL, area_size, + PROT_READ | PROT_WRITE, + MAP_ANONYMOUS | MAP_PRIVATE, + 0, 0); + +Create refill ring +------------------ + +Allocate memory for a shared ringbuf used for returning consumed buffers:: + + void *ring_ptr = mmap(NULL, ring_size, + PROT_READ | PROT_WRITE, + MAP_ANONYMOUS | MAP_PRIVATE, + 0, 0); + +This refill ring consists of some space for the header, followed by an array of +``struct io_uring_zcrx_rqe``:: + + size_t rq_entries = 4096; + size_t ring_size = rq_entries * sizeof(struct io_uring_zcrx_rqe) + PAGE_SIZE; + /* align to page size */ + ring_size = (ring_size + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1); + +Register ZC Rx +-------------- + +Fill in registration structs:: + + struct io_uring_zcrx_area_reg area_reg = { + .addr = (__u64)(unsigned long)area_ptr, + .len = area_size, + .flags = 0, + }; + + struct io_uring_region_desc region_reg = { + .user_addr = (__u64)(unsigned long)ring_ptr, + .size = ring_size, + .flags = IORING_MEM_REGION_TYPE_USER, + }; + + struct io_uring_zcrx_ifq_reg reg = { + .if_idx = if_nametoindex("eth0"), + /* this is the HW queue with desired flow steered into it */ + .if_rxq = 1, + .rq_entries = rq_entries, + .area_ptr = (__u64)(unsigned long)&area_reg, + .region_ptr = (__u64)(unsigned long)®ion_reg, + }; + +Register with kernel:: + + io_uring_register_ifq(ring, ®); + +Map refill ring +--------------- + +The kernel fills in fields for the refill ring in the registration ``struct +io_uring_zcrx_ifq_reg``. Map it into userspace:: + + struct io_uring_zcrx_rq refill_ring; + + refill_ring.khead = (unsigned *)((char *)ring_ptr + reg.offsets.head); + refill_ring.khead = (unsigned *)((char *)ring_ptr + reg.offsets.tail); + refill_ring.rqes = + (struct io_uring_zcrx_rqe *)((char *)ring_ptr + reg.offsets.rqes); + refill_ring.rq_tail = 0; + refill_ring.ring_ptr = ring_ptr; + +Receiving data +-------------- + +Prepare a zero copy recv request:: + + struct io_uring_sqe *sqe; + + sqe = io_uring_get_sqe(ring); + io_uring_prep_rw(IORING_OP_RECV_ZC, sqe, fd, NULL, 0, 0); + sqe->ioprio |= IORING_RECV_MULTISHOT; + +Now, submit and wait:: + + io_uring_submit_and_wait(ring, 1); + +Finally, process completions:: + + struct io_uring_cqe *cqe; + unsigned int count = 0; + unsigned int head; + + io_uring_for_each_cqe(ring, head, cqe) { + struct io_uring_zcrx_cqe *rcqe = (struct io_uring_zcrx_cqe *)(cqe + 1); + + unsigned long mask = (1ULL << IORING_ZCRX_AREA_SHIFT) - 1; + unsigned char *data = area_ptr + (rcqe->off & mask); + /* do something with the data */ + + count++; + } + io_uring_cq_advance(ring, count); + +Recycling buffers +----------------- + +Return buffers back to the kernel to be used again:: + + struct io_uring_zcrx_rqe *rqe; + unsigned mask = refill_ring.ring_entries - 1; + rqe = &refill_ring.rqes[refill_ring.rq_tail & mask]; + + unsigned long area_offset = rcqe->off & ~IORING_ZCRX_AREA_MASK; + rqe->off = area_offset | area_reg.rq_area_token; + rqe->len = cqe->res; + IO_URING_WRITE_ONCE(*refill_ring.ktail, ++refill_ring.rq_tail); + +Testing +======= + +See ``tools/testing/selftests/drivers/net/hw/iou-zcrx.c``