From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-x104a.google.com (mail-pj1-x104a.google.com [IPv6:2607:f8b0:4864:20::104a]) by mail.toke.dk (Postfix) with ESMTPS id 09FAFA2A371 for ; Thu, 14 Sep 2023 23:05:14 +0200 (CEST) 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=jINT7tzU Received: by mail-pj1-x104a.google.com with SMTP id 98e67ed59e1d1-26f3fce5b45so1288641a91.3 for ; Thu, 14 Sep 2023 14:05:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1694725512; x=1695330312; 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=13spL0Rm0ZGXcXIcH5DSZIzgePO9nUsV+W7OjRfRCTw=; b=jINT7tzUaUrpFMmNbu7Tbuhg9OO3QerzndxfcOKP7MB/Jh855eV8tstYhc8XnPxI86 hz6Q2DTSeTvkr2gdudfZwpslVzZY3Ucg+366NghCO39w258XJMIeL1LL3WpqVPntB9ES 4wbbe4vcJ6PK1NWL0l7vnEYOjXxhPnuYt10Mo1M0CMKIN3Dckm3J4RSSFdfDS1Fe9p4z C/dTzwDgpXBxGxkWSBkpfLcZlJMP1di7rLMxUDCNqF70dLwxIwpZFO/UnbtYvMlikEWV BzRhNJLJHt8FWRiWlRPR/WEWr3lwx3VA8Ewlxs1YS11zlMjaUridx0pCpHtcjJewyOLG C5GA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1694725512; x=1695330312; 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=13spL0Rm0ZGXcXIcH5DSZIzgePO9nUsV+W7OjRfRCTw=; b=E9aY0wjSLoFcvofyzyWFynbFAgXMZfP2zPftIUxnEAa+7l3XBCXNUNtO4ZxWO+mkUd Sys/OjLvb9oRcxdGgCS1D6eyvDCQ4HL7s6acEC+U5YZ5Xdvdx4qMcL1R2LpOGXo8e4Ms ynR67y+eV3E0za5xNuMVzhF/PUYraTqLRMC+6WxlX3Xs6a6EBq3pGMvJV8vjlwiroSmD E/CEx+umchpkr76ca2VpYs3ZsGEnupmD5z1rf37AEgYbqibuRoNKs8UdL0SWjoMZNTqR byMGuJ/tFvvykyVDQTBatemZQxnhM3X2FCuEBOZDwY9aKWWRsxUx9EHrLyIObQN+H72e +esA== X-Gm-Message-State: AOJu0Yz54UFUfdEpGdpfgYrMc/3F0uMsPyMLK77WkJ56PmZPAa/osmd9 eZoBG8bQOIkMo/FRXLpSGVBPT6U= X-Google-Smtp-Source: AGHT+IEMN2hG9dtM5YRRKewCpdKoIKPR7ONPikbZ6FD/09kibOLr5RACjhIMih7flqe4lTNsti13Q60= X-Received: from sdf.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5935]) (user=sdf job=sendgmr) by 2002:a17:90a:df8a:b0:271:df39:2332 with SMTP id p10-20020a17090adf8a00b00271df392332mr165599pjv.9.1694725512346; Thu, 14 Sep 2023 14:05:12 -0700 (PDT) Date: Thu, 14 Sep 2023 14:04:52 -0700 In-Reply-To: <20230914210452.2588884-1-sdf@google.com> Mime-Version: 1.0 References: <20230914210452.2588884-1-sdf@google.com> X-Mailer: git-send-email 2.42.0.459.ge4e396fd5e-goog Message-ID: <20230914210452.2588884-10-sdf@google.com> From: Stanislav Fomichev To: bpf@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Message-ID-Hash: 5HX6IF73K2FFL7STMEOL4J2JG5BLZKVV X-Message-ID-Hash: 5HX6IF73K2FFL7STMEOL4J2JG5BLZKVV X-MailFrom: 3iHUDZQMKCa8hSUVddVaT.RdbmSe-WXcihmSe-egdYTRi.cTi@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 v2 9/9] 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/xsk-tx-metadata.rst | 77 ++++++++++++++++++++ 2 files changed, 78 insertions(+) create mode 100644 Documentation/networking/xsk-tx-metadata.rst diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst index 5b75c3f7a137..9b2accb48df7 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/xsk-tx-metadata.rst b/Documentation/networking/xsk-tx-metadata.rst new file mode 100644 index 000000000000..b7289f06745c --- /dev/null +++ b/Documentation/networking/xsk-tx-metadata.rst @@ -0,0 +1,77 @@ +================== +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_TX_METADATA_TIMESTAMP``: requests the device to put transmission + timestamp into ``tx_timestamp`` field of ``union xsk_tx_metadata``. +- ``XDP_TX_METADATA_CHECKSUM``: requests the device to calculate L4 + checksum. ``csum_start`` specifies byte offset of there the checksumming + should start and ``csum_offset`` specifies byte offset where the + device should store the computed checksum. +- ``XDP_TX_METADATA_CHECKSUM_SW``: requests checksum calculation to + be done in software; this mode works only in ``XSK_COPY`` mode and + is mostly intended for testing. Do not enable this option, it + will negatively affect performance. + +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 not 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_TX_METADATA_TIMESTAMP`` +- ``tx-checksum``: device supports ``XDP_TX_METADATA_CHECKSUM`` + +Note that every devices supports ``XDP_TX_METADATA_CHECKSUM_SW`` when +running in ``XSK_COPY`` mode. + +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. -- 2.42.0.459.ge4e396fd5e-goog