ceph/src/spdk/dpdk/doc/guides/sample_app_ug/skeleton.rst

   1 ..  SPDX-License-Identifier: BSD-3-Clause
   2     Copyright(c) 2015 Intel Corporation.
   3
   4 Basic Forwarding Sample Application
   5 ===================================
   6
   7 The Basic Forwarding sample application is a simple *skeleton* example of a
   8 forwarding application.
   9
  10 It is intended as a demonstration of the basic components of a DPDK forwarding
  11 application. For more detailed implementations see the L2 and L3 forwarding
  12 sample applications.
  13
  14 Compiling the Application
  15 -------------------------
  16
  17 To compile the sample application see :doc:`compiling`.
  18
  19 The application is located in the ``skeleton`` sub-directory.
  20
  21 Running the Application
  22 -----------------------
  23
  24 To run the example in a ``linux`` environment:
  25
  26 .. code-block:: console
  27
  28     ./build/basicfwd -l 1 -n 4
  29
  30 Refer to *DPDK Getting Started Guide* for general information on running
  31 applications and the Environment Abstraction Layer (EAL) options.
  32
  33
  34 Explanation
  35 -----------
  36
  37 The following sections provide an explanation of the main components of the
  38 code.
  39
  40 All DPDK library functions used in the sample code are prefixed with ``rte_``
  41 and are explained in detail in the *DPDK API Documentation*.
  42
  43
  44 The Main Function
  45 ~~~~~~~~~~~~~~~~~
  46
  47 The ``main()`` function performs the initialization and calls the execution
  48 threads for each lcore.
  49
  50 The first task is to initialize the Environment Abstraction Layer (EAL).  The
  51 ``argc`` and ``argv`` arguments are provided to the ``rte_eal_init()``
  52 function. The value returned is the number of parsed arguments:
  53
  54 .. code-block:: c
  55
  56     int ret = rte_eal_init(argc, argv);
  57     if (ret < 0)
  58         rte_exit(EXIT_FAILURE, "Error with EAL initialization\n");
  59
  60
  61 The ``main()`` also allocates a mempool to hold the mbufs (Message Buffers)
  62 used by the application:
  63
  64 .. code-block:: c
  65
  66     mbuf_pool = rte_mempool_create("MBUF_POOL",
  67                                    NUM_MBUFS * nb_ports,
  68                                    MBUF_SIZE,
  69                                    MBUF_CACHE_SIZE,
  70                                    sizeof(struct rte_pktmbuf_pool_private),
  71                                    rte_pktmbuf_pool_init, NULL,
  72                                    rte_pktmbuf_init,      NULL,
  73                                    rte_socket_id(),
  74                                    0);
  75
  76 Mbufs are the packet buffer structure used by DPDK. They are explained in
  77 detail in the "Mbuf Library" section of the *DPDK Programmer's Guide*.
  78
  79 The ``main()`` function also initializes all the ports using the user defined
  80 ``port_init()`` function which is explained in the next section:
  81
  82 .. code-block:: c
  83
  84     RTE_ETH_FOREACH_DEV(portid) {
  85         if (port_init(portid, mbuf_pool) != 0) {
  86             rte_exit(EXIT_FAILURE,
  87                      "Cannot init port %" PRIu8 "\n", portid);
  88         }
  89     }
  90
  91
  92 Once the initialization is complete, the application is ready to launch a
  93 function on an lcore. In this example ``lcore_main()`` is called on a single
  94 lcore.
  95
  96
  97 .. code-block:: c
  98
  99         lcore_main();
 100
 101 The ``lcore_main()`` function is explained below.
 102
 103
 104
 105 The Port Initialization  Function
 106 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 107
 108 The main functional part of the port initialization used in the Basic
 109 Forwarding application is shown below:
 110
 111 .. code-block:: c
 112
 113     static inline int
 114     port_init(uint16_t port, struct rte_mempool *mbuf_pool)
 115     {
 116         struct rte_eth_conf port_conf = port_conf_default;
 117         const uint16_t rx_rings = 1, tx_rings = 1;
 118         struct rte_ether_addr addr;
 119         int retval;
 120         uint16_t q;
 121
 122         if (!rte_eth_dev_is_valid_port(port))
 123             return -1;
 124
 125         /* Configure the Ethernet device. */
 126         retval = rte_eth_dev_configure(port, rx_rings, tx_rings, &port_conf);
 127         if (retval != 0)
 128             return retval;
 129
 130         /* Allocate and set up 1 RX queue per Ethernet port. */
 131         for (q = 0; q < rx_rings; q++) {
 132             retval = rte_eth_rx_queue_setup(port, q, RX_RING_SIZE,
 133                     rte_eth_dev_socket_id(port), NULL, mbuf_pool);
 134             if (retval < 0)
 135                 return retval;
 136         }
 137
 138         /* Allocate and set up 1 TX queue per Ethernet port. */
 139         for (q = 0; q < tx_rings; q++) {
 140             retval = rte_eth_tx_queue_setup(port, q, TX_RING_SIZE,
 141                     rte_eth_dev_socket_id(port), NULL);
 142             if (retval < 0)
 143                 return retval;
 144         }
 145
 146         /* Start the Ethernet port. */
 147         retval = rte_eth_dev_start(port);
 148         if (retval < 0)
 149             return retval;
 150
 151         /* Enable RX in promiscuous mode for the Ethernet device. */
 152         retval = rte_eth_promiscuous_enable(port);
 153         if (retval != 0)
 154             return retval;
 155
 156         return 0;
 157     }
 158
 159 The Ethernet ports are configured with default settings using the
 160 ``rte_eth_dev_configure()`` function and the ``port_conf_default`` struct:
 161
 162 .. code-block:: c
 163
 164     static const struct rte_eth_conf port_conf_default = {
 165         .rxmode = { .max_rx_pkt_len = RTE_ETHER_MAX_LEN }
 166     };
 167
 168 For this example the ports are set up with 1 RX and 1 TX queue using the
 169 ``rte_eth_rx_queue_setup()`` and ``rte_eth_tx_queue_setup()`` functions.
 170
 171 The Ethernet port is then started:
 172
 173 .. code-block:: c
 174
 175         retval  = rte_eth_dev_start(port);
 176
 177
 178 Finally the RX port is set in promiscuous mode:
 179
 180 .. code-block:: c
 181
 182         retval = rte_eth_promiscuous_enable(port);
 183
 184
 185 The Lcores Main
 186 ~~~~~~~~~~~~~~~
 187
 188 As we saw above the ``main()`` function calls an application function on the
 189 available lcores. For the Basic Forwarding application the lcore function
 190 looks like the following:
 191
 192 .. code-block:: c
 193
 194     static __rte_noreturn void
 195     lcore_main(void)
 196     {
 197         uint16_t port;
 198
 199         /*
 200          * Check that the port is on the same NUMA node as the polling thread
 201          * for best performance.
 202          */
 203         RTE_ETH_FOREACH_DEV(port)
 204             if (rte_eth_dev_socket_id(port) > 0 &&
 205                     rte_eth_dev_socket_id(port) !=
 206                             (int)rte_socket_id())
 207                 printf("WARNING, port %u is on remote NUMA node to "
 208                         "polling thread.\n\tPerformance will "
 209                         "not be optimal.\n", port);
 210
 211         printf("\nCore %u forwarding packets. [Ctrl+C to quit]\n",
 212                 rte_lcore_id());
 213
 214         /* Run until the application is quit or killed. */
 215         for (;;) {
 216             /*
 217              * Receive packets on a port and forward them on the paired
 218              * port. The mapping is 0 -> 1, 1 -> 0, 2 -> 3, 3 -> 2, etc.
 219              */
 220             RTE_ETH_FOREACH_DEV(port) {
 221
 222                 /* Get burst of RX packets, from first port of pair. */
 223                 struct rte_mbuf *bufs[BURST_SIZE];
 224                 const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
 225                         bufs, BURST_SIZE);
 226
 227                 if (unlikely(nb_rx == 0))
 228                     continue;
 229
 230                 /* Send burst of TX packets, to second port of pair. */
 231                 const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
 232                         bufs, nb_rx);
 233
 234                 /* Free any unsent packets. */
 235                 if (unlikely(nb_tx < nb_rx)) {
 236                     uint16_t buf;
 237                     for (buf = nb_tx; buf < nb_rx; buf++)
 238                         rte_pktmbuf_free(bufs[buf]);
 239                 }
 240             }
 241         }
 242     }
 243
 244
 245 The main work of the application is done within the loop:
 246
 247 .. code-block:: c
 248
 249         for (;;) {
 250             RTE_ETH_FOREACH_DEV(port) {
 251
 252                 /* Get burst of RX packets, from first port of pair. */
 253                 struct rte_mbuf *bufs[BURST_SIZE];
 254                 const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
 255                         bufs, BURST_SIZE);
 256
 257                 if (unlikely(nb_rx == 0))
 258                     continue;
 259
 260                 /* Send burst of TX packets, to second port of pair. */
 261                 const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
 262                         bufs, nb_rx);
 263
 264                 /* Free any unsent packets. */
 265                 if (unlikely(nb_tx < nb_rx)) {
 266                     uint16_t buf;
 267                     for (buf = nb_tx; buf < nb_rx; buf++)
 268                         rte_pktmbuf_free(bufs[buf]);
 269                 }
 270             }
 271         }
 272
 273 Packets are received in bursts on the RX ports and transmitted in bursts on
 274 the TX ports. The ports are grouped in pairs with a simple mapping scheme
 275 using the an XOR on the port number::
 276
 277     0 -> 1
 278     1 -> 0
 279
 280     2 -> 3
 281     3 -> 2
 282
 283     etc.
 284
 285 The ``rte_eth_tx_burst()`` function frees the memory buffers of packets that
 286 are transmitted. If packets fail to transmit, ``(nb_tx < nb_rx)``, then they
 287 must be freed explicitly using ``rte_pktmbuf_free()``.
 288
 289 The forwarding loop can be interrupted and the application closed using
 290 ``Ctrl-C``.