doc: add basic forwarding skeleton user guide
Added a sample application guide for the basic forwarding /skeleton app. Signed-off-by: John McNamara <john.mcnamara@intel.com> Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
This commit is contained in:
John McNamara
Thomas Monjalon
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@ -465,7 +465,9 @@ M: John McNamara <john.mcnamara@intel.com>
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F: examples/rxtx_callbacks/
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M: Bruce Richardson <bruce.richardson@intel.com>
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M: John McNamara <john.mcnamara@intel.com>
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F: examples/skeleton/
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F: doc/guides/sample_app_ug/skeleton.rst
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F: examples/vmdq/
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F: examples/vmdq_dcb/
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@ -1,5 +1,5 @@
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.. BSD LICENSE
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Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
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Copyright(c) 2010-2015 Intel Corporation. All rights reserved.
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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@ -43,6 +43,7 @@ Sample Applications User Guide
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cmd_line
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exception_path
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hello_world
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skeleton
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ip_frag
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ipv4_multicast
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ip_reassembly
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338
doc/guides/sample_app_ug/skeleton.rst
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338
doc/guides/sample_app_ug/skeleton.rst
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@ -0,0 +1,338 @@
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.. BSD LICENSE
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Copyright(c) 2015 Intel Corporation. All rights reserved.
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in
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the documentation and/or other materials provided with the
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distribution.
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* Neither the name of Intel Corporation nor the names of its
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contributors may be used to endorse or promote products derived
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from this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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Basic Forwarding Sample Application
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===================================
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The Basic Forwarding sample application is a simple *skeleton* example of a
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forwarding application.
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It is intended as a demonstration of the basic components of a DPDK forwarding
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application. For more detailed implementations see the L2 and L3 forwarding
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sample applications.
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Compiling the Application
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-------------------------
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To compile the application export the path to the DPDK source tree and go to
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the example directory:
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.. code-block:: console
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export RTE_SDK=/path/to/rte_sdk
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cd ${RTE_SDK}/examples/skeleton
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Set the target, for example:
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.. code-block:: console
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export RTE_TARGET=x86_64-native-linuxapp-gcc
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See the *DPDK Getting Started* Guide for possible ``RTE_TARGET`` values.
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Build the application as follows:
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.. code-block:: console
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make
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Running the Application
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-----------------------
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To run the example in a ``linuxapp`` environment:
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.. code-block:: console
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./build/basicfwd -c 2 -n 4
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Refer to *DPDK Getting Started Guide* for general information on running
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applications and the Environment Abstraction Layer (EAL) options.
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Explanation
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-----------
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The following sections provide an explanation of the main components of the
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code.
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All DPDK library functions used in the sample code are prefixed with ``rte_``
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and are explained in detail in the *DPDK API Documentation*.
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The Main Function
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~~~~~~~~~~~~~~~~~
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The ``main()`` function performs the initialization and calls the execution
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threads for each lcore.
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The first task is to initialize the Environment Abstraction Layer (EAL). The
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``argc`` and ``argv`` arguments are provided to the ``rte_eal_init()``
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function. The value returned is the number of parsed arguments:
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.. code-block:: c
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int ret = rte_eal_init(argc, argv);
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if (ret < 0)
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rte_exit(EXIT_FAILURE, "Error with EAL initialization\n");
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The ``main()`` also allocates a mempool to hold the mbufs (Message Buffers)
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used by the application:
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.. code-block:: c
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mbuf_pool = rte_mempool_create("MBUF_POOL",
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NUM_MBUFS * nb_ports,
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MBUF_SIZE,
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MBUF_CACHE_SIZE,
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sizeof(struct rte_pktmbuf_pool_private),
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rte_pktmbuf_pool_init, NULL,
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rte_pktmbuf_init, NULL,
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rte_socket_id(),
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0);
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Mbufs are the packet buffer structure used by DPDK. They are explained in
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detail in the "Mbuf Library" section of the *DPDK Programmer's Guide*.
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The ``main()`` function also initializes all the ports using the user defined
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``port_init()`` function which is explained in the next section:
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.. code-block:: c
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for (portid = 0; portid < nb_ports; portid++) {
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if (port_init(portid, mbuf_pool) != 0) {
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rte_exit(EXIT_FAILURE,
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"Cannot init port %" PRIu8 "\n", portid);
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}
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}
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Once the initialization is complete, the application is ready to launch a
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function on an lcore. In this example ``lcore_main()`` is called on a single
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lcore.
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.. code-block:: c
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lcore_main();
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The ``lcore_main()`` function is explained below.
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The Port Initialization Function
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The main functional part of the port initialization used in the Basic
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Forwarding application is shown below:
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.. code-block:: c
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static inline int
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port_init(uint8_t port, struct rte_mempool *mbuf_pool)
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{
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struct rte_eth_conf port_conf = port_conf_default;
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const uint16_t rx_rings = 1, tx_rings = 1;
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struct ether_addr addr;
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int retval;
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uint16_t q;
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if (port >= rte_eth_dev_count())
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return -1;
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/* Configure the Ethernet device. */
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retval = rte_eth_dev_configure(port, rx_rings, tx_rings, &port_conf);
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if (retval != 0)
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return retval;
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/* Allocate and set up 1 RX queue per Ethernet port. */
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for (q = 0; q < rx_rings; q++) {
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retval = rte_eth_rx_queue_setup(port, q, RX_RING_SIZE,
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rte_eth_dev_socket_id(port), NULL, mbuf_pool);
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if (retval < 0)
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return retval;
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}
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/* Allocate and set up 1 TX queue per Ethernet port. */
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for (q = 0; q < tx_rings; q++) {
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retval = rte_eth_tx_queue_setup(port, q, TX_RING_SIZE,
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rte_eth_dev_socket_id(port), NULL);
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if (retval < 0)
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return retval;
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}
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/* Start the Ethernet port. */
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retval = rte_eth_dev_start(port);
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if (retval < 0)
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return retval;
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/* Enable RX in promiscuous mode for the Ethernet device. */
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rte_eth_promiscuous_enable(port);
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return 0;
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}
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The Ethernet ports are configured with default settings using the
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``rte_eth_dev_configure()`` function and the ``port_conf_default`` struct:
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.. code-block:: c
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static const struct rte_eth_conf port_conf_default = {
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.rxmode = { .max_rx_pkt_len = ETHER_MAX_LEN }
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};
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For this example the ports are set up with 1 RX and 1 TX queue using the
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``rte_eth_rx_queue_setup()`` and ``rte_eth_tx_queue_setup()`` functions.
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The Ethernet port is then started:
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.. code-block:: c
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retval = rte_eth_dev_start(port);
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Finally the RX port is set in promiscuous mode:
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.. code-block:: c
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rte_eth_promiscuous_enable(port);
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The Lcores Main
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~~~~~~~~~~~~~~~
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As we saw above the ``main()`` function calls an application function on the
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available lcores. For the Basic Forwarding application the lcore function
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looks like the following:
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.. code-block:: c
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static __attribute__((noreturn)) void
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lcore_main(void)
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{
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const uint8_t nb_ports = rte_eth_dev_count();
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uint8_t port;
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/*
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* Check that the port is on the same NUMA node as the polling thread
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* for best performance.
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*/
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for (port = 0; port < nb_ports; port++)
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if (rte_eth_dev_socket_id(port) > 0 &&
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rte_eth_dev_socket_id(port) !=
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(int)rte_socket_id())
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printf("WARNING, port %u is on remote NUMA node to "
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"polling thread.\n\tPerformance will "
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"not be optimal.\n", port);
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printf("\nCore %u forwarding packets. [Ctrl+C to quit]\n",
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rte_lcore_id());
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/* Run until the application is quit or killed. */
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for (;;) {
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/*
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* Receive packets on a port and forward them on the paired
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* port. The mapping is 0 -> 1, 1 -> 0, 2 -> 3, 3 -> 2, etc.
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*/
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for (port = 0; port < nb_ports; port++) {
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/* Get burst of RX packets, from first port of pair. */
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struct rte_mbuf *bufs[BURST_SIZE];
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const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
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bufs, BURST_SIZE);
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if (unlikely(nb_rx == 0))
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continue;
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/* Send burst of TX packets, to second port of pair. */
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const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
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bufs, nb_rx);
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/* Free any unsent packets. */
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if (unlikely(nb_tx < nb_rx)) {
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uint16_t buf;
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for (buf = nb_tx; buf < nb_rx; buf++)
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rte_pktmbuf_free(bufs[buf]);
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}
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}
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}
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}
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The main work of the application is done within the loop:
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.. code-block:: c
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for (;;) {
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for (port = 0; port < nb_ports; port++) {
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/* Get burst of RX packets, from first port of pair. */
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struct rte_mbuf *bufs[BURST_SIZE];
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const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
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bufs, BURST_SIZE);
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if (unlikely(nb_rx == 0))
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continue;
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/* Send burst of TX packets, to second port of pair. */
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const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
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bufs, nb_rx);
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/* Free any unsent packets. */
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if (unlikely(nb_tx < nb_rx)) {
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uint16_t buf;
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for (buf = nb_tx; buf < nb_rx; buf++)
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rte_pktmbuf_free(bufs[buf]);
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}
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}
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}
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Packets are received in bursts on the RX ports and transmitted in bursts on
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the TX ports. The ports are grouped in pairs with a simple mapping scheme
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using the an XOR on the port number::
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0 -> 1
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1 -> 0
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2 -> 3
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3 -> 2
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etc.
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The ``rte_eth_tx_burst()`` function frees the memory buffers of packets that
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are transmitted. If packets fail to transmit, ``(nb_tx < nb_rx)``, then they
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must be freed explicitly using ``rte_pktmbuf_free()``.
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The forwarding loop can be interrupted and the application closed using
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``Ctrl-C``.
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