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Distributor Sample Application
==============================

The distributor sample application is a simple example of packet distribution
to cores using the Data Plane Development Kit (DPDK).

Overview
--------

The distributor application performs the distribution of packets that are received
on an RX_PORT to different cores. When processed by the cores, the destination
port of a packet is the port from the enabled port mask adjacent to the one on
which the packet was received, that is, if the first four ports are enabled
(port mask 0xf), ports 0 and 1 RX/TX into each other, and ports 2 and 3 RX/TX
into each other.

This application can be used to benchmark performance using the traffic
generator as shown in the figure below.

.. _figure_dist_perf:

.. figure:: img/dist_perf.*

   Performance Benchmarking Setup (Basic Environment)


Compiling the Application
-------------------------

#.  Go to the sample application directory:

    ..  code-block:: console

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

#.  Set the target (a default target is used if not specified). For example:

    ..  code-block:: console

        export RTE_TARGET=x86_64-native-linuxapp-gcc

    See the DPDK Getting Started Guide for possible RTE_TARGET values.

#.  Build the application:

    ..  code-block:: console

        make

Running the Application
-----------------------

#. The application has a number of command line options:

   ..  code-block:: console

       ./build/distributor_app [EAL options] -- -p PORTMASK

   where,

   *   -p PORTMASK: Hexadecimal bitmask of ports to configure

#. To run the application in linuxapp environment with 10 lcores, 4 ports,
   issue the command:

   ..  code-block:: console

       $ ./build/distributor_app -c 0x4003fe -n 4 -- -p f

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

Explanation
-----------

The distributor application consists of three types of threads: a receive
thread (lcore_rx()), a set of worker threads(lcore_worker())
and a transmit thread(lcore_tx()). How these threads work together is shown
in :numref:`figure_dist_app` below. The main() function launches  threads of these three types.
Each thread has a while loop which will be doing processing and which is
terminated only upon SIGINT or ctrl+C. The receive and transmit threads
communicate using a software ring (rte_ring structure).

The receive thread receives the packets using rte_eth_rx_burst() and gives
them to  the distributor (using rte_distributor_process() API) which will
be called in context of the receive thread itself. The distributor distributes
the packets to workers threads based on the tagging of the packet -
indicated by the hash field in the mbuf. For IP traffic, this field is
automatically filled by the NIC with the "usr" hash value for the packet,
which works as a per-flow tag.

More than one worker thread can exist as part of the application, and these
worker threads do simple packet processing by requesting packets from
the distributor, doing a simple XOR operation on the input port mbuf field
(to indicate the output port which will be used later for packet transmission)
and then finally returning the packets back to the distributor in the RX thread.

Meanwhile, the receive thread will call the distributor api
rte_distributor_returned_pkts() to get the packets processed, and will enqueue
them to a ring for transfer to the TX thread for transmission on the output port.
The transmit thread will dequeue the packets from the ring and transmit them on
the output port specified in packet mbuf.

Users who wish to terminate the running of the application have to press ctrl+C
(or send SIGINT to the app). Upon this signal, a signal handler provided
in the application will terminate all running threads gracefully and print
final statistics to the user.

.. _figure_dist_app:

.. figure:: img/dist_app.*

   Distributor Sample Application Layout


Debug Logging Support
---------------------

Debug logging is provided as part of the application; the user needs to uncomment
the line "#define DEBUG" defined in start of the application in main.c to enable debug logs.

Statistics
----------

Upon SIGINT (or) ctrl+C, the print_stats() function displays the count of packets
processed at the different stages in the application.

Application Initialization
--------------------------

Command line parsing is done in the same way as it is done in the L2 Forwarding Sample
Application. See Section 9.4.1, "Command Line Arguments".

Mbuf pool initialization is done in the same way as it is done in the L2 Forwarding
Sample Application. See Section 9.4.2, "Mbuf Pool Initialization".

Driver Initialization is done in same way as it is done in the L2 Forwarding Sample
Application. See Section 9.4.3, "Driver Initialization".

RX queue initialization is done in the same way as it is done in the L2 Forwarding
Sample Application. See Section 9.4.4, "RX Queue Initialization".

TX queue initialization is done in the same way as it is done in the L2 Forwarding
Sample Application. See Section 9.4.5, "TX Queue Initialization".
