5. Hello World Sample Application

The Hello World sample application is an example of the simplest DPDK application that can be written. The application simply prints an “helloworld” message on every enabled lcore.

5.1. Compiling the Application

Go to the example directory:

export RTE_SDK=/path/to/rte_sdk
cd ${RTE_SDK}/examples/helloworld

Set the target (a default target is used if not specified). For example:
```
export RTE_TARGET=x86_64-native-linuxapp-gcc
```
See the DPDK Getting Started Guide for possible RTE_TARGET values.
Build the application:
```
make
```

5.2. Running the Application

To run the example in a linuxapp environment:

$ ./build/helloworld -l 0-3 -n 4

Refer to DPDK Getting Started Guide for general information on running applications and the Environment Abstraction Layer (EAL) options.

5.3. Explanation

The following sections provide some explanation of code.

5.3.1. EAL Initialization

The first task is to initialize the Environment Abstraction Layer (EAL). This is done in the main() function using the following code:

int

main(int argc, char **argv)

{
    ret = rte_eal_init(argc, argv);
    if (ret < 0)
        rte_panic("Cannot init EAL\n");

This call finishes the initialization process that was started before main() is called (in case of a Linuxapp environment). The argc and argv arguments are provided to the rte_eal_init() function. The value returned is the number of parsed arguments.

5.3.2. Starting Application Unit Lcores

Once the EAL is initialized, the application is ready to launch a function on an lcore. In this example, lcore_hello() is called on every available lcore. The following is the definition of the function:

static int
lcore_hello( attribute ((unused)) void *arg)
{
    unsigned lcore_id;

    lcore_id = rte_lcore_id();
    printf("hello from core %u\n", lcore_id);
    return 0;
}

The code that launches the function on each lcore is as follows:

/* call lcore_hello() on every slave lcore */

RTE_LCORE_FOREACH_SLAVE(lcore_id) {
   rte_eal_remote_launch(lcore_hello, NULL, lcore_id);
}

/* call it on master lcore too */

lcore_hello(NULL);

The following code is equivalent and simpler:

rte_eal_mp_remote_launch(lcore_hello, NULL, CALL_MASTER);

Refer to the DPDK API Reference for detailed information on the rte_eal_mp_remote_launch() function.