7be78d0279
The tool comes from https://github.com/jsoref Signed-off-by: Josh Soref <jsoref@gmail.com> Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
75 lines
3.0 KiB
ReStructuredText
75 lines
3.0 KiB
ReStructuredText
.. SPDX-License-Identifier: BSD-3-Clause
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Copyright(c) 2018 Intel Corporation.
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AF_PACKET Poll Mode Driver
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==========================
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The AF_PACKET socket in Linux allows an application to receive and send raw
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packets. This Linux-specific PMD binds to an AF_PACKET socket and allows
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a DPDK application to send and receive raw packets through the Kernel.
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In order to improve Rx and Tx performance this implementation makes use of
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PACKET_MMAP, which provides a mmapped ring buffer, shared between user space
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and kernel, that's used to send and receive packets. This helps reducing system
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calls and the copies needed between user space and Kernel.
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The PACKET_FANOUT_HASH behavior of AF_PACKET is used for frame reception.
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Options and inherent limitations
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--------------------------------
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The following options can be provided to set up an af_packet port in DPDK.
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Some of these, in turn, will be used to configure the PACKET_MMAP settings.
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* ``iface`` - name of the Kernel interface to attach to (required);
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* ``qpairs`` - number of Rx and Tx queues (optional, default 1);
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* ``qdisc_bypass`` - set PACKET_QDISC_BYPASS option in AF_PACKET (optional,
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disabled by default);
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* ``blocksz`` - PACKET_MMAP block size (optional, default 4096);
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* ``framesz`` - PACKET_MMAP frame size (optional, default 2048B; Note: multiple
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of 16B);
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* ``framecnt`` - PACKET_MMAP frame count (optional, default 512).
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Because this implementation is based on PACKET_MMAP, and PACKET_MMAP has its
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own pre-requisites, it should be noted that the inner workings of PACKET_MMAP
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should be carefully considered before modifying some of these options (namely,
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``blocksz``, ``framesz`` and ``framecnt`` above).
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As an example, if one changes ``framesz`` to be 1024B, it is expected that
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``blocksz`` is set to at least 1024B as well (although 2048B in this case would
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allow two "frames" per "block").
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This restriction happens because PACKET_MMAP expects each single "frame" to fit
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inside of a "block". And although multiple "frames" can fit inside of a single
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"block", a "frame" may not span across two "blocks".
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For the full details behind PACKET_MMAP's structures and settings, consider
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reading the `PACKET_MMAP documentation in the Kernel
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<https://www.kernel.org/doc/Documentation/networking/packet_mmap.txt>`_.
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Prerequisites
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-------------
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This is a Linux-specific PMD, thus the following prerequisites apply:
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* A Linux Kernel;
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* A Kernel bound interface to attach to (e.g. a tap interface).
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Set up an af_packet interface
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-----------------------------
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The following example will set up an af_packet interface in DPDK with the
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default options described above (blocksz=4096B, framesz=2048B and
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framecnt=512):
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.. code-block:: console
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--vdev=eth_af_packet0,iface=tap0,blocksz=4096,framesz=2048,framecnt=512,qpairs=1,qdisc_bypass=0
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Features and Limitations
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------------------------
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The PMD will re-insert the VLAN tag transparently to the packet if the kernel
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strips it, as long as the ``RTE_ETH_RX_OFFLOAD_VLAN_STRIP`` is not enabled by the
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application.
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