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Compiling and Running Sample Applications
=========================================

The chapter describes how to compile and run applications in an DPDK environment.
It also provides a pointer to where sample applications are stored.

.. note::

    Parts of this process can also be done using the setup script described the
    :ref:`linux_setup_script` section of this document.

Compiling a Sample Application
------------------------------

Once an DPDK target environment directory has been created (such as ``x86_64-native-linuxapp-gcc``),
it contains all libraries and header files required to build an application.

When compiling an application in the Linux* environment on the DPDK, the following variables must be exported:

* ``RTE_SDK`` - Points to the DPDK installation directory.

* ``RTE_TARGET`` - Points to the DPDK target environment directory.

The following is an example of creating the ``helloworld`` application, which runs in the DPDK Linux environment.
This example may be found in the ``${RTE_SDK}/examples`` directory.

The directory contains the ``main.c`` file. This file, when combined with the libraries in the DPDK target environment,
calls the various functions to initialize the DPDK environment,
then launches an entry point (dispatch application) for each core to be utilized.
By default, the binary is generated in the build directory.

.. code-block:: console

    cd examples/helloworld/
    export RTE_SDK=$HOME/DPDK
    export RTE_TARGET=x86_64-native-linuxapp-gcc

    make
        CC main.o
        LD helloworld
        INSTALL-APP helloworld
        INSTALL-MAP helloworld.map

    ls build/app
        helloworld helloworld.map

.. note::

    In the above example, ``helloworld`` was in the directory structure of the DPDK.
    However, it could have been located outside the directory structure to keep the DPDK structure intact.
    In the following case, the ``helloworld`` application is copied to a new directory as a new starting point.

    .. code-block:: console

       export RTE_SDK=/home/user/DPDK
       cp -r $(RTE_SDK)/examples/helloworld my_rte_app
       cd my_rte_app/
       export RTE_TARGET=x86_64-native-linuxapp-gcc

       make
         CC main.o
         LD helloworld
         INSTALL-APP helloworld
         INSTALL-MAP helloworld.map

Running a Sample Application
----------------------------

.. warning::

    The UIO drivers and hugepages must be setup prior to running an application.

.. warning::

    Any ports to be used by the application must be already bound to an appropriate kernel
    module, as described in :ref:`linux_gsg_binding_kernel`, prior to running the application.

The application is linked with the DPDK target environment's Environmental Abstraction Layer (EAL) library,
which provides some options that are generic to every DPDK application.

The following is the list of options that can be given to the EAL:

.. code-block:: console

    ./rte-app -c COREMASK [-n NUM] [-b <domain:bus:devid.func>] \
              [--socket-mem=MB,...] [-m MB] [-r NUM] [-v] [--file-prefix] \
	      [--proc-type <primary|secondary|auto>] [-- xen-dom0]

The EAL options are as follows:

* ``-c COREMASK``:
  An hexadecimal bit mask of the cores to run on. Note that core numbering can
  change between platforms and should be determined beforehand.

* ``-n NUM``:
  Number of memory channels per processor socket.

* ``-b <domain:bus:devid.func>``:
  Blacklisting of ports; prevent EAL from using specified PCI device
  (multiple ``-b`` options are allowed).

* ``--use-device``:
  use the specified Ethernet device(s) only. Use comma-separate
  ``[domain:]bus:devid.func`` values. Cannot be used with ``-b`` option.

* ``--socket-mem``:
  Memory to allocate from hugepages on specific sockets.

* ``-m MB``:
  Memory to allocate from hugepages, regardless of processor socket. It is
  recommended that ``--socket-mem`` be used instead of this option.

* ``-r NUM``:
  Number of memory ranks.

* ``-v``:
  Display version information on startup.

* ``--huge-dir``:
  The directory where hugetlbfs is mounted.

* ``--file-prefix``:
  The prefix text used for hugepage filenames.

* ``--proc-type``:
  The type of process instance.

* ``--xen-dom0``:
  Support application running on Xen Domain0 without hugetlbfs.

* ``--vmware-tsc-map``:
  Use VMware TSC map instead of native RDTSC.

* ``--base-virtaddr``:
  Specify base virtual address.

* ``--vfio-intr``:
  Specify interrupt type to be used by VFIO (has no effect if VFIO is not used).

The ``-c`` and option is mandatory; the others are optional.

Copy the DPDK application binary to your target, then run the application as follows
(assuming the platform has four memory channels per processor socket,
and that cores 0-3 are present and are to be used for running the application)::

    ./helloworld -c f -n 4

.. note::

    The ``--proc-type`` and ``--file-prefix`` EAL options are used for running
    multiple DPDK processes. See the "Multi-process Sample Application"
    chapter in the *DPDK Sample Applications User Guide* and the *DPDK
    Programmers Guide* for more details.

Logical Core Use by Applications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The coremask parameter is always mandatory for DPDK applications.
Each bit of the mask corresponds to the equivalent logical core number as reported by Linux.
Since these logical core numbers, and their mapping to specific cores on specific NUMA sockets, can vary from platform to platform,
it is recommended that the core layout for each platform be considered when choosing the coremask to use in each case.

On initialization of the EAL layer by an DPDK application, the logical cores to be used and their socket location are displayed.
This information can also be determined for all cores on the system by examining the ``/proc/cpuinfo`` file, for example, by running cat ``/proc/cpuinfo``.
The physical id attribute listed for each processor indicates the CPU socket to which it belongs.
This can be useful when using other processors to understand the mapping of the logical cores to the sockets.

.. note::

    A more graphical view of the logical core layout may be obtained using the ``lstopo`` Linux utility.
    On Fedora Linux, this may be installed and run using the following command::

        sudo yum install hwloc
        ./lstopo

.. warning::

    The logical core layout can change between different board layouts and should be checked before selecting an application coremask.

Hugepage Memory Use by Applications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When running an application, it is recommended to use the same amount of memory as that allocated for hugepages.
This is done automatically by the DPDK application at startup,
if no ``-m`` or ``--socket-mem`` parameter is passed to it when run.

If more memory is requested by explicitly passing a ``-m`` or ``--socket-mem`` value, the application fails.
However, the application itself can also fail if the user requests less memory than the reserved amount of hugepage-memory, particularly if using the ``-m`` option.
The reason is as follows.
Suppose the system has 1024 reserved 2 MB pages in socket 0 and 1024 in socket 1.
If the user requests 128 MB of memory, the 64 pages may not match the constraints:

*   The hugepage memory by be given to the application by the kernel in socket 1 only.
    In this case, if the application attempts to create an object, such as a ring or memory pool in socket 0, it fails.
    To avoid this issue, it is recommended that the ``--socket-mem`` option be used instead of the ``-m`` option.

*   These pages can be located anywhere in physical memory, and, although the DPDK EAL will attempt to allocate memory in contiguous blocks,
    it is possible that the pages will not be contiguous. In this case, the application is not able to allocate big memory pools.

The socket-mem option can be used to request specific amounts of memory for specific sockets.
This is accomplished by supplying the ``--socket-mem`` flag followed by amounts of memory requested on each socket,
for example, supply ``--socket-mem=0,512`` to try and reserve 512 MB for socket 1 only.
Similarly, on a four socket system, to allocate 1 GB memory on each of sockets 0 and 2 only, the parameter ``--socket-mem=1024,0,1024`` can be used.
No memory will be reserved on any CPU socket that is not explicitly referenced, for example, socket 3 in this case.
If the DPDK cannot allocate enough memory on each socket, the EAL initialization fails.

Additional Sample Applications
------------------------------

Additional sample applications are included in the ${RTE_SDK}/examples directory.
These sample applications may be built and run in a manner similar to that described in earlier sections in this manual.
In addition, see the *DPDK Sample Applications User Guide* for a description of the application,
specific instructions on compilation and execution and some explanation of the code.

Additional Test Applications
----------------------------

In addition, there are two other applications that are built when the libraries are created.
The source files for these are in the DPDK/app directory and are called test and testpmd.
Once the libraries are created, they can be found in the build/app directory.

*   The test application provides a variety of specific tests for the various functions in the DPDK.

*   The testpmd application provides a number of different packet throughput tests and
    examples of features such as how to use the Flow Director found in the Intel® 82599 10 Gigabit Ethernet Controller.
