Multiple Devices

This example show how to take advantage of multiple FPGAs on a system. It will show how to initialized an OpenCL context, allocate memory on the two devices and execute a kernel on each FPGA.

KEY CONCEPTS: OpenCL Host APIs, Multi-FPGA Execution, Event Handling

KEYWORDS: xcl::get_xil_devices

This example demonstrates how multiple FPGA devices can be configured on a system.

OpenCL context and queues are initialized for each FPGA.

contexts[d] =cl::Context(devices[d], props, nullptr, nullptr, &err);
queues[d] = cl::CommandQueue(contexts[d], devices[d], CL_QUEUE_PROFILING_ENABLE, &err);

Each FPGA device needs to be loaded and programmed with binary file and a kernel each is created for FPGAs on the system.

fileBuf[d] = xcl::read_binary_file(binaryFile, fileBufSize);
bins[d].push_back({fileBuf[d], fileBufSize});
programs[d] = load_cl2_binary(bins[d], devices[d], contexts[d]);
kernels[d] = cl::Kernel(programs[d], "vadd", &err);

Buffers are also created for each FPGA seperately.

buffer_a[d] = cl::Buffer(contexts[d], CL_MEM_USE_HOST_PTR | CL_MEM_READ_ONLY, size_per_device, &A[offset], &err);

Following table summarizes the observations while running the design on 1 and 2 U50 platforms:

Device Count	Time Taken(s)
1	47.41
2	23.71
Speedup	1.99

EXCLUDED PLATFORMS

Platforms containing following strings in their names are not supported for this example :

nodma

DESIGN FILES

Application code is located in the src directory. Accelerator binary files will be compiled to the xclbin directory. The xclbin directory is required by the Makefile and its contents will be filled during compilation. A listing of all the files in this example is shown below

src/host.cpp
src/vector_addition.cpp

Access these files in the github repo by clicking here.

COMMAND LINE ARGUMENTS

Once the environment has been configured, the application can be executed by

./multiple_devices <vector_addition XCLBIN>