From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by mail.toke.dk (Postfix) with ESMTPS id 4E4E2A40612 for ; Mon, 27 Nov 2023 20:03:33 +0100 (CET) Authentication-Results: mail.toke.dk; dkim=pass (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20230601 header.b=3KGNzCPp Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-5cddc35545dso46241697b3.2 for ; Mon, 27 Nov 2023 11:03:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1701111812; x=1701716612; darn=xdp-project.net; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=zp0NfVT6k+O+cDddTZy09JqchV8tKkVXuv7rsNqmLRk=; b=3KGNzCPpisxXZsI8QwbXICp0LDBDgOWUNc9r5xNMdGgxfMiv2c0hrWAJFD6+z5/uSZ MkCItQDeL6UcynzOZ4L9CZ2tP/TeATdKEfuc/+JdskO2pzZPHSYmrC9RqyWjYG2F54vo tpky97H6kySDSF1pJSKedXIsHnt9o6Gm/h3uajTuRStIMdOAKas2qE7jP1mHaSjMS6XB 9I27meUYQyxUShReLl7yo/Ttng1dHkxlkhnLgLG/iBot0y9iIVxgHJ9no8MrexBZAqEA Wzusp9FjQF0GGaiJGfxm8bhvGEGr9BDfpxZ48OZqkXKvTHI6Jb6u5lw1iJ1XSF6NghsK R1Mg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701111812; x=1701716612; 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=zp0NfVT6k+O+cDddTZy09JqchV8tKkVXuv7rsNqmLRk=; b=h7SbhkFIHrjxrUqfdYx/mM1pDgppT9hmVIvTYGgZCVXPcu8lV5trWByKpEyw+rwwPd CU/nX+e2TQs5W7/KmsA/JC33ju7z4IgLY4c68oNpWzD1DlIE/4LsHlEPTC6K/ZiKdkyT PTm9czasCD3xXYzN2n6mU+PvRSnlwx9iYWq2iRj0zaK+gf+uqX+asBGirpy7MoHhzILH ERh46JlbjLgcKO4YwREX4jEYb6o2vTuLlTZfNZnKZMdMzhgf7liXQPsYUBhPABFdqTe2 buopBUfXmJX8ziRMr8dltlhbzqgKn//BXWnXxeUeDQNa1Wpgw3dBltll6V9AKx1GWpDQ rn3A== X-Gm-Message-State: AOJu0Yxj6R7Qtfm5G0U33l6kR7nRr6Mjo7hdN+aHg6BGjXmlx/LsLZFS nJn6yKPCe0rAnnxuzbRDFGM7icc= X-Google-Smtp-Source: AGHT+IFD35ro+x7PheJe+DmDJlu2/a0Hzt5yVOIeVEMuqqZBdyVEqsELGNDZNdlVsxO3j8SPEB5mPXE= X-Received: from sdf.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5935]) (user=sdf job=sendgmr) by 2002:a05:690c:844:b0:5cb:d84d:218c with SMTP id bz4-20020a05690c084400b005cbd84d218cmr415973ywb.0.1701111812437; Mon, 27 Nov 2023 11:03:32 -0800 (PST) Date: Mon, 27 Nov 2023 11:03:12 -0800 In-Reply-To: <20231127190319.1190813-1-sdf@google.com> Mime-Version: 1.0 References: <20231127190319.1190813-1-sdf@google.com> X-Mailer: git-send-email 2.43.0.rc1.413.gea7ed67945-goog Message-ID: <20231127190319.1190813-7-sdf@google.com> From: Stanislav Fomichev To: bpf@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Message-ID-Hash: 4IXWZXA2LFABKKTVH3FGMMIML3XRC6WU X-Message-ID-Hash: 4IXWZXA2LFABKKTVH3FGMMIML3XRC6WU X-MailFrom: 3BOhkZQMKCZkL689HH9E7.5HFQ6I-ABGMLQ6I-IKHC75M.G7M@flex--sdf.bounces.google.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, kuba@kernel.org, toke@kernel.org, willemb@google.com, dsahern@kernel.org, magnus.karlsson@intel.com, bjorn@kernel.org, maciej.fijalkowski@intel.com, hawk@kernel.org, yoong.siang.song@intel.com, netdev@vger.kernel.org, xdp-hints@xdp-project.net X-Mailman-Version: 3.3.8 Precedence: list Subject: [xdp-hints] [PATCH bpf-next v6 06/13] xsk: Document tx_metadata_len layout List-Id: XDP hardware hints design discussion Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: - how to use - how to query features - pointers to the examples Signed-off-by: Stanislav Fomichev --- Documentation/networking/index.rst | 1 + Documentation/networking/xdp-rx-metadata.rst | 2 + Documentation/networking/xsk-tx-metadata.rst | 70 ++++++++++++++++++++ 3 files changed, 73 insertions(+) create mode 100644 Documentation/networking/xsk-tx-metadata.rst diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst index 683eb42309cc..a297a894b366 100644 --- a/Documentation/networking/index.rst +++ b/Documentation/networking/index.rst @@ -123,6 +123,7 @@ Refer to :ref:`netdev-FAQ` for a guide on netdev development process specifics. xfrm_sync xfrm_sysctl xdp-rx-metadata + xsk-tx-metadata .. only:: subproject and html diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst index 205696780b78..e3e9420fd817 100644 --- a/Documentation/networking/xdp-rx-metadata.rst +++ b/Documentation/networking/xdp-rx-metadata.rst @@ -1,3 +1,5 @@ +.. SPDX-License-Identifier: GPL-2.0 + =============== XDP RX Metadata =============== diff --git a/Documentation/networking/xsk-tx-metadata.rst b/Documentation/networking/xsk-tx-metadata.rst new file mode 100644 index 000000000000..4f376560b23f --- /dev/null +++ b/Documentation/networking/xsk-tx-metadata.rst @@ -0,0 +1,70 @@ +================== +AF_XDP TX Metadata +================== + +This document describes how to enable offloads when transmitting packets +via :doc:`af_xdp`. Refer to :doc:`xdp-rx-metadata` on how to access similar +metadata on the receive side. + +General Design +============== + +The headroom for the metadata is reserved via ``tx_metadata_len`` in +``struct xdp_umem_reg``. The metadata length is therefore the same for +every socket that shares the same umem. The metadata layout is a fixed UAPI, +refer to ``union xsk_tx_metadata`` in ``include/uapi/linux/if_xdp.h``. +Thus, generally, the ``tx_metadata_len`` field above should contain +``sizeof(union xsk_tx_metadata)``. + +The headroom and the metadata itself should be located right before +``xdp_desc->addr`` in the umem frame. Within a frame, the metadata +layout is as follows:: + + tx_metadata_len + / \ + +-----------------+---------+----------------------------+ + | xsk_tx_metadata | padding | payload | + +-----------------+---------+----------------------------+ + ^ + | + xdp_desc->addr + +An AF_XDP application can request headrooms larger than ``sizeof(struct +xsk_tx_metadata)``. The kernel will ignore the padding (and will still +use ``xdp_desc->addr - tx_metadata_len`` to locate +the ``xsk_tx_metadata``). For the frames that shouldn't carry +any metadata (i.e., the ones that don't have ``XDP_TX_METADATA`` option), +the metadata area is ignored by the kernel as well. + +The flags field enables the particular offload: + +- ``XDP_TXMD_FLAGS_TIMESTAMP``: requests the device to put transmission + timestamp into ``tx_timestamp`` field of ``union xsk_tx_metadata``. +- ``XDP_TXMD_FLAGS_CHECKSUM``: requests the device to calculate L4 + checksum. ``csum_start`` specifies byte offset of where the checksumming + should start and ``csum_offset`` specifies byte offset where the + device should store the computed checksum. + +Besides the flags above, in order to trigger the offloads, the first +packet's ``struct xdp_desc`` descriptor should set ``XDP_TX_METADATA`` +bit in the ``options`` field. Also note that in a multi-buffer packet +only the first chunk should carry the metadata. + +Querying Device Capabilities +============================ + +Every devices exports its offloads capabilities via netlink netdev family. +Refer to ``xsk-flags`` features bitmask in +``Documentation/netlink/specs/netdev.yaml``. + +- ``tx-timestamp``: device supports ``XDP_TXMD_FLAGS_TIMESTAMP`` +- ``tx-checksum``: device supports ``XDP_TXMD_FLAGS_CHECKSUM`` + +See ``tools/net/ynl/samples/netdev.c`` on how to query this information. + +Example +======= + +See ``tools/testing/selftests/bpf/xdp_hw_metadata.c`` for an example +program that handles TX metadata. Also see https://github.com/fomichev/xskgen +for a more bare-bones example. -- 2.43.0.rc1.413.gea7ed67945-goog