8728ccf376
Some DPDK applications wrongly assume these requirements:
- no hotplug, i.e. ports are never detached
- all allocated ports are available to the application
Such application iterates over ports by its own mean.
The most common pattern is to request the port count and
assume ports with index in the range [0..count[ can be used.
There are three consequences when using such wrong design:
- new ports having an index higher than the port count won't be seen
- old ports being detached (RTE_ETH_DEV_UNUSED) can be seen as ghosts
- failsafe sub-devices (RTE_ETH_DEV_DEFERRED) will be seen by the application
Such mistake will be less common with growing hotplug awareness.
All applications and examples inside this repository - except testpmd -
must be fixed to use the iterator RTE_ETH_FOREACH_DEV.
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
290 lines
8.5 KiB
ReStructuredText
290 lines
8.5 KiB
ReStructuredText
.. SPDX-License-Identifier: BSD-3-Clause
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Copyright(c) 2015 Intel Corporation.
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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 sample application see :doc:`compiling`.
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The application is located in the ``skeleton`` sub-directory.
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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 -l 1 -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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RTE_ETH_FOREACH_DEV(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(uint16_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 uint16_t nb_ports = rte_eth_dev_count();
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uint16_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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RTE_ETH_FOREACH_DEV(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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RTE_ETH_FOREACH_DEV(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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RTE_ETH_FOREACH_DEV(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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