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

To compile the sample application see Compiling the Sample Applications.

The application is located in the helloworld sub-directory.

5.2. Running the Application

To run the example in a linux environment:

$ ./<build_dir>/examples/dpdk-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:

main(int argc, char **argv)
	int ret;
	unsigned lcore_id;

	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 Linux 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(__rte_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:

	/* Simpler equivalent. 8< */
	rte_eal_remote_launch(lcore_hello, NULL, lcore_id);
	/* >8 End of simpler equivalent. */

/* call it on main lcore too */

The following code is equivalent and simpler:

rte_eal_remote_launch(lcore_hello, NULL, lcore_id);

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