Multicore Execution using Dataflow Domain

This example shows how to speed up execution of models using dataflow domain in Simulink. We use the digital up converter and digital down converter blocks to create a family radio service transmitter and receiver.

Introduction

Dataflow execution domain allows you to make use of multiple cores in the simulation of computationally intensive signal processing systems.

This example shows how to specify dataflow as the execution domain of a subsystem, improve simulation performance of the model, and generate multicore code.

Family Radio Service System

This example uses the Digital Up-Converter (DUC) and Digital Down-Converter (DDC) blocks to create a Family Radio Service (FRS) transmitter and receiver. The Digital Up-Converter (DUC) block converts a complex digital baseband signal to real passband signal. The Digital Down-Converter (DDC) block converts the digitized real signal back to a baseband complex signal. Open familyRadioServiceExample model.

Simulate the model and measure the execution time. Execution time is measured using the output of the sim command which returns the simulation execution time of the model. To measure the time taken primarily for the Dataflow subsystem, comment out the Spectrum Analyzer blocks and Audio Device Writer block.

Simulation execution time for single-threaded model = 3.48s

Specify Dataflow Execution Domain

In Simulink, you specify dataflow as the execution domain for a subsystem by setting the Domain parameter to Dataflow using Property Inspector. You can view the Property Inspector for a subsystem, first by selecting the subsystem and then selecting View>Property Inspector. In the Property Inspector, you can set the domain to dataflow by selecting Set domain specification and then choosing "Dataflow" for "Domain" setting. You can also use Dataflow Subsystem block from the Dataflow library of DSP System toolbox to get a subsystem that is preconfigured with the dataflow execution domain.

The Dataflow subsystem automatically partitions the blocks for multicore execution.

Multicore Simulation of Dataflow Domain

Dataflow domains automatically partition your model and simulate the system using multiple threads for better simulation performance. You can use the Dataflow Simulation Assistant to analyze the Dataflow Subsystem and further improve the simulation performance. You can open the assistant by clicking on the Dataflow assistant button below the Automatic frame size calculation parameter in Property Inspector.

The Dataflow Simulation Assistant suggests changing model settings for optimal simulation performance. To accept the proposed model settings, next to Suggested model settings for simulation performance, click Accept all. Alternatively, you can expand the section to change the settings individually. In the Dataflow Simulation Assistant, click the Analyze button to start the analysis of the dataflow domain for simulation performance. Once the analysis is finished, the Dataflow Simulation Assistant shows how many threads the dataflow subsystem will use during simulation.

After analyzing the model, the assistant shows one thread because the data dependency between the blocks in the model prevents blocks from being executed concurrently. By pipelining the data dependent blocks, the Dataflow Subsystem can increase concurrency for higher data throughput. Dataflow Simulation Assistant shows the recommended number of pipeline delays as Suggested Latency. The suggested latency value is computed to give the best performance.

The following diagram shows the Dataflow Simulation Assistant where the Dataflow Subsystem currently specifies a latency value of 0, and the suggested latency for the system is 3.

Click the Accept button next to Suggested Latency in the Dataflow Simulation Assistant to use the recommended latency for the Dataflow Subsystem. This value can also be entered directly in the Property Inspector for "Latency" parameter. Simulink shows the latency parameter value using $Z^{-1}$ tags at the output ports of the dataflow subsystem.

Dataflow Simulation Assistant now shows the number of threads as 2 meaning that the blocks inside the dataflow subsystem simulate in parallel using 2 threads.

Compensating for Latency

When latency is increased in the dataflow execution domain to break data dependencies between blocks and create concurrency, that delay needs to be accounted for in other parts of the model. For example, signals that are compared or combined with the signals at the output ports of the Dataflow Subsystem must be delayed to align in time with the signals at the output ports of the Dataflow Subsystem. In this example, the audio signal from the source block that goes to the Audio Device Writer must be delayed to align with other signals. To compensate for the latency specified on the dataflow subsystem, use a delay block to delay this signal by 2 frames. For this signal, the frame length is 1000. A delay value of 2000 is set in the delay block to align the signal from source and the signal processed through Dataflow Subsystem.

Dataflow Simulation Performance

Simulate the model and measure model execution time. When measuring the time taken for simulating the model, comment out the Spectrum Analyzer blocks and Audio Device Writer blocks to measure the time taken primarily for the Dataflow Subsystem. Execution time is measured using the sim command, which returns the simulation execution time of the model. We can measure the amount of speedup obtained by dividing the execution time taken by the model using multiple threads with the execution time taken by the original model. This number is computed and shown below.

These numbers and analysis were published on a Windows desktop computer with Intel® Xeon® CPU W-2133 @ 3.6 GHz 6 Cores 12 Threads processor.

Simulation execution time for multithreaded model = 2.21s
Actual speedup with dataflow: 1.6x

Code Generation

Code generation requires a Simulink Coder™ or an Embedded Coder® license. Press Ctrl+B to build the model and generate single-core code for your desktop target. If your desktop machine is Windows or Linux, you can generate multicore code for the model. To enable multicore code generation for the model, you must select the Allow tasks to execute concurrently on target parameter in the Solver pane under Solver details. Selecting this parameter allows:

Each rate in the model to execute as an independent concurrent task on the target processor
The dataflow subsystem to generate additional concurrent tasks by automatically partitioning the blocks

In the generated code you can observe the generated functions for each concurrent task created by the dataflow domain and realized as an OpenMP section.

Summary

This example shows how to specify dataflow as the execution domain in a model to design computationally-intensive signal processing systems, improve simulation performance of the model and generate multicore code.

Documentation