.. SPDX-License-Identifier: BSD-3-Clause
Copyright(c) 2015 Intel Corporation.
Basic Forwarding Sample Application
===================================
The Basic Forwarding sample application is a simple *skeleton* example of a
forwarding application.
It is intended as a demonstration of the basic components of a DPDK forwarding
application. For more detailed implementations see the L2 and L3 forwarding
sample applications.
Compiling the Application
-------------------------
To compile the sample application see :doc:`compiling`.
The application is located in the ``skeleton`` sub-directory.
Running the Application
-----------------------
To run the example in a ``linux`` environment:
.. code-block:: console
./<build_dir>/examples/dpdk-skeleton -l 1 -n 4
Refer to *DPDK Getting Started Guide* for general information on running
applications and the Environment Abstraction Layer (EAL) options.
Explanation
-----------
The following sections provide an explanation of the main components of the
code.
All DPDK library functions used in the sample code are prefixed with ``rte_``
and are explained in detail in the *DPDK API Documentation*.
The Main Function
~~~~~~~~~~~~~~~~~
The ``main()`` function performs the initialization and calls the execution
threads for each lcore.
The first task is to initialize the Environment Abstraction Layer (EAL). The
``argc`` and ``argv`` arguments are provided to the ``rte_eal_init()``
function. The value returned is the number of parsed arguments:
.. code-block:: c
int ret = rte_eal_init(argc, argv);
if (ret < 0)
rte_exit(EXIT_FAILURE, "Error with EAL initialization\n");
The ``main()`` also allocates a mempool to hold the mbufs (Message Buffers)
used by the application:
.. code-block:: c
mbuf_pool = rte_mempool_create("MBUF_POOL",
NUM_MBUFS * nb_ports,
MBUF_SIZE,
MBUF_CACHE_SIZE,
sizeof(struct rte_pktmbuf_pool_private),
rte_pktmbuf_pool_init, NULL,
rte_pktmbuf_init, NULL,
rte_socket_id(),
0);
Mbufs are the packet buffer structure used by DPDK. They are explained in
detail in the "Mbuf Library" section of the *DPDK Programmer's Guide*.
The ``main()`` function also initializes all the ports using the user defined
``port_init()`` function which is explained in the next section:
.. code-block:: c
RTE_ETH_FOREACH_DEV(portid) {
if (port_init(portid, mbuf_pool) != 0) {
rte_exit(EXIT_FAILURE,
"Cannot init port %" PRIu8 "\n", portid);
}
}
Once the initialization is complete, the application is ready to launch a
function on an lcore. In this example ``lcore_main()`` is called on a single
lcore.
.. code-block:: c
lcore_main();
The ``lcore_main()`` function is explained below.
The Port Initialization Function
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The main functional part of the port initialization used in the Basic
Forwarding application is shown below:
.. code-block:: c
static inline int
port_init(uint16_t port, struct rte_mempool *mbuf_pool)
{
struct rte_eth_conf port_conf = port_conf_default;
const uint16_t rx_rings = 1, tx_rings = 1;
struct rte_ether_addr addr;
int retval;
uint16_t q;
if (!rte_eth_dev_is_valid_port(port))
return -1;
/* Configure the Ethernet device. */
retval = rte_eth_dev_configure(port, rx_rings, tx_rings, &port_conf);
if (retval != 0)
return retval;
/* Allocate and set up 1 RX queue per Ethernet port. */
for (q = 0; q < rx_rings; q++) {
retval = rte_eth_rx_queue_setup(port, q, RX_RING_SIZE,
rte_eth_dev_socket_id(port), NULL, mbuf_pool);
if (retval < 0)
return retval;
}
/* Allocate and set up 1 TX queue per Ethernet port. */
for (q = 0; q < tx_rings; q++) {
retval = rte_eth_tx_queue_setup(port, q, TX_RING_SIZE,
rte_eth_dev_socket_id(port), NULL);
if (retval < 0)
return retval;
}
/* Start the Ethernet port. */
retval = rte_eth_dev_start(port);
if (retval < 0)
return retval;
/* Enable RX in promiscuous mode for the Ethernet device. */
retval = rte_eth_promiscuous_enable(port);
if (retval != 0)
return retval;
return 0;
}
The Ethernet ports are configured with default settings using the
``rte_eth_dev_configure()`` function and the ``port_conf_default`` struct:
.. code-block:: c
static const struct rte_eth_conf port_conf_default = {
.rxmode = { .max_rx_pkt_len = RTE_ETHER_MAX_LEN }
};
For this example the ports are set up with 1 RX and 1 TX queue using the
``rte_eth_rx_queue_setup()`` and ``rte_eth_tx_queue_setup()`` functions.
The Ethernet port is then started:
.. code-block:: c
retval = rte_eth_dev_start(port);
Finally the RX port is set in promiscuous mode:
.. code-block:: c
retval = rte_eth_promiscuous_enable(port);
The Lcores Main
~~~~~~~~~~~~~~~
As we saw above the ``main()`` function calls an application function on the
available lcores. For the Basic Forwarding application the lcore function
looks like the following:
.. code-block:: c
static __rte_noreturn void
lcore_main(void)
{
uint16_t port;
/*
* Check that the port is on the same NUMA node as the polling thread
* for best performance.
*/
RTE_ETH_FOREACH_DEV(port)
if (rte_eth_dev_socket_id(port) > 0 &&
rte_eth_dev_socket_id(port) !=
(int)rte_socket_id())
printf("WARNING, port %u is on remote NUMA node to "
"polling thread.\n\tPerformance will "
"not be optimal.\n", port);
printf("\nCore %u forwarding packets. [Ctrl+C to quit]\n",
rte_lcore_id());
/* Run until the application is quit or killed. */
for (;;) {
/*
* Receive packets on a port and forward them on the paired
* port. The mapping is 0 -> 1, 1 -> 0, 2 -> 3, 3 -> 2, etc.
*/
RTE_ETH_FOREACH_DEV(port) {
/* Get burst of RX packets, from first port of pair. */
struct rte_mbuf *bufs[BURST_SIZE];
const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
bufs, BURST_SIZE);
if (unlikely(nb_rx == 0))
continue;
/* Send burst of TX packets, to second port of pair. */
const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
bufs, nb_rx);
/* Free any unsent packets. */
if (unlikely(nb_tx < nb_rx)) {
uint16_t buf;
for (buf = nb_tx; buf < nb_rx; buf++)
rte_pktmbuf_free(bufs[buf]);
}
}
}
}
The main work of the application is done within the loop:
.. code-block:: c
for (;;) {
RTE_ETH_FOREACH_DEV(port) {
/* Get burst of RX packets, from first port of pair. */
struct rte_mbuf *bufs[BURST_SIZE];
const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
bufs, BURST_SIZE);
if (unlikely(nb_rx == 0))
continue;
/* Send burst of TX packets, to second port of pair. */
const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
bufs, nb_rx);
/* Free any unsent packets. */
if (unlikely(nb_tx < nb_rx)) {
uint16_t buf;
for (buf = nb_tx; buf < nb_rx; buf++)
rte_pktmbuf_free(bufs[buf]);
}
}
}
Packets are received in bursts on the RX ports and transmitted in bursts on
the TX ports. The ports are grouped in pairs with a simple mapping scheme
using the an XOR on the port number::
0 -> 1
1 -> 0
2 -> 3
3 -> 2
etc.
The ``rte_eth_tx_burst()`` function frees the memory buffers of packets that
are transmitted. If packets fail to transmit, ``(nb_tx < nb_rx)``, then they
must be freed explicitly using ``rte_pktmbuf_free()``.
The forwarding loop can be interrupted and the application closed using
``Ctrl-C``.