As of commit 364e08f2bbc0, DPDK allows an aplication to send and receive raw packets using an AF_PACKET and PACKET_MMAP, when using a Linux Kernel. This complements it by adding a simple guide with the following information: - An introduction, where a brief explanation of this driver is given, pointing out the dependency on PACKET_MMAP; - Which options are supported at configuration time, while setting up an interface, and it's inherent limitations; - What the prerequisites are; - A command line example of how to set up a DPDK port using the af_packet driver.
Since there's a dependency in PACKET_MMAP, the guide also points to the original Kernel documentation, so the reader can get more details. Signed-off-by: Tiago Lam <tiago....@intel.com> --- doc/guides/nics/af_packet.rst | 67 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 doc/guides/nics/af_packet.rst diff --git a/doc/guides/nics/af_packet.rst b/doc/guides/nics/af_packet.rst new file mode 100644 index 0000000..e6f77ad --- /dev/null +++ b/doc/guides/nics/af_packet.rst @@ -0,0 +1,67 @@ +.. SPDX-License-Identifier: BSD-3-Clause + Copyright(c) 2018 Intel Corporation. + +AF_PACKET Poll Mode Driver +========================== + +The AF_PACKET socket in Linux allows an application to receive and send raw +packets. This Linux-specific PMD driver binds to an AF_PACKET socket and allows +a DPDK application to send and receive raw packets through the Kernel. + +In order to improve Rx and Tx performance this implementation makes use of +PACKET_MMAP, which provides a mmap'ed ring buffer, shared between user space +and kernel, that's used to send and receive packets. This helps reducing system +calls and the copies needed between user space and Kernel. + +The PACKET_FANOUT_HASH behaviour of AF_PACKET is used for frame reception. + +Options and inherent limitations +-------------------------------- + +The following options can be provided to set up an af_packet port in DPDK. +Some of these, in turn, will be used to configure the PAKET_MMAP settings. + +* "iface" - name of the Kernel interface to attach to (required); +* "qpairs" - number of Rx and Tx queues (optional, default 1); +* "qdisc_bypass" - set PACKET_QDISC_BYPASS option in AF_PACKET (optional, + disabled by default); +* "blocksz" - PACKET_MMAP block size (optional, default 4096); +* "framesz" - PACKET_MMAP frame size (optional, default 2048B; Note: multiple + of 16B); +* "framecnt" - PACKET_MMAP frame count (optional, default 512B). + +Because this implementation is based on PACKET_MMAP, and PACKET_MMAP has its +own pre-requisites, it should be noted that the inner workings of PACKET_MMAP +should be carefully considered before modifying some of these options (namely, +"blocksz, "framesz" and "framecnt" above). + +As an example, if one changes "framesz" to be 1024B, it is expected that +"blocksz" is set to at least 1024B as well (although 2048B in this case would +allow two "frames" per "block"). + +This restriction happens because PACKET_MMAP expects each single "frame" to fit +inside of a "block". And although multiple "frames" can fit inside of a single +"block", a "frame" may not span across two "blocks". + +For the full details behind PACKET_MMAP's structures and settings, consider +reading the `PACKET_MMAP documentation in the Kernel +<https://www.kernel.org/doc/Documentation/networking/packet_mmap.txt>`_. + +Prerequisites +------------- + +This is a Linux-specific PMD, thus the following prerequisites apply: + +* A Linux Kernel; +* A Kernel bound interface to attach to (e.g. a tap interface). + +Set up an af_packet interface +----------------------------- + +The following example will set up an af_packet interface in DPDK with the +default options described above (blocksz=4096B, framesz=2048B and +framecnt=512B): + +.. code-block:: console + + --vdev=eth_af_packet0,iface=tap0,blocksz=4096,framesz=2048,framecnt=512,qpairs=1,qdisc_bypass=0 -- 2.7.4