35. Distributor Sample Application

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

35.1. 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.

Fig. 35.1 Performance Benchmarking Setup (Basic Environment)

35.2. Compiling the Application

Go to the sample application directory:

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:
```
export RTE_TARGET=x86_64-native-linuxapp-gcc
```
See the DPDK Getting Started Guide for possible RTE_TARGET values.
Build the application:
```
make
```

35.3. Running the Application

The application has a number of command line options:
```
./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:
```
$ ./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.

35.4. 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 Fig. 35.2 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.

Fig. 35.2 Distributor Sample Application Layout

35.5. 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.

35.6. Statistics

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

35.7. Application Initialization

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

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

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

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

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