ceph/src/dpdk/doc/guides/sample_app_ug/hello_world.rst

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  30
  31 Hello World Sample Application
  32 ==============================
  33
  34 The Hello World sample application is an example of the simplest DPDK application that can be written.
  35 The application simply prints an "helloworld" message on every enabled lcore.
  36
  37 Compiling the Application
  38 -------------------------
  39
  40 #.  Go to the example directory:
  41
  42     .. code-block:: console
  43
  44         export RTE_SDK=/path/to/rte_sdk
  45         cd ${RTE_SDK}/examples/helloworld
  46
  47 #.  Set the target (a default target is used if not specified). For example:
  48
  49     .. code-block:: console
  50
  51         export RTE_TARGET=x86_64-native-linuxapp-gcc
  52
  53     See the *DPDK Getting Started* Guide for possible RTE_TARGET values.
  54
  55 #.  Build the application:
  56
  57     .. code-block:: console
  58
  59         make
  60
  61 Running the Application
  62 -----------------------
  63
  64 To run the example in a linuxapp environment:
  65
  66 .. code-block:: console
  67
  68     $ ./build/helloworld -c f -n 4
  69
  70 Refer to *DPDK Getting Started Guide* for general information on running applications
  71 and the Environment Abstraction Layer (EAL) options.
  72
  73 Explanation
  74 -----------
  75
  76 The following sections provide some explanation of code.
  77
  78 EAL Initialization
  79 ~~~~~~~~~~~~~~~~~~
  80
  81 The first task is to initialize the Environment Abstraction Layer (EAL).
  82 This is done in the main() function using the following code:
  83
  84 .. code-block:: c
  85
  86     int
  87
  88     main(int argc, char **argv)
  89
  90     {
  91         ret = rte_eal_init(argc, argv);
  92         if (ret < 0)
  93             rte_panic("Cannot init EAL\n");
  94
  95 This call finishes the initialization process that was started before main() is called (in case of a Linuxapp environment).
  96 The argc and argv arguments are provided to the rte_eal_init() function.
  97 The value returned is the number of parsed arguments.
  98
  99 Starting Application Unit Lcores
 100 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 101
 102 Once the EAL is initialized, the application is ready to launch a function on an lcore.
 103 In this example, lcore_hello() is called on every available lcore.
 104 The following is the definition of the function:
 105
 106 .. code-block:: c
 107
 108     static int
 109     lcore_hello( attribute ((unused)) void *arg)
 110     {
 111         unsigned lcore_id;
 112
 113         lcore_id = rte_lcore_id();
 114         printf("hello from core %u\n", lcore_id);
 115         return 0;
 116     }
 117
 118 The code that launches the function on each lcore is as follows:
 119
 120 .. code-block:: c
 121
 122     /* call lcore_hello() on every slave lcore */
 123
 124     RTE_LCORE_FOREACH_SLAVE(lcore_id) {
 125        rte_eal_remote_launch(lcore_hello, NULL, lcore_id);
 126     }
 127
 128     /* call it on master lcore too */
 129
 130     lcore_hello(NULL);
 131
 132 The following code is equivalent and simpler:
 133
 134 .. code-block:: c
 135
 136     rte_eal_mp_remote_launch(lcore_hello, NULL, CALL_MASTER);
 137
 138 Refer to the *DPDK API Reference* for detailed information on the rte_eal_mp_remote_launch() function.