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SYCL Academy

Exercise 3: Hello World

In this first exercise you will learn:

  • How to create and submit a command group.
  • How to define a SYCL kernel function.
  • How to stream output from a SYCL kernel function.

Once you have a queue you can now submit work to be executed on your chosen device and this is done via command groups, which are made up of commands and data dependencies.

1.) Define a command group

Define a lambda to represent your command group and pass it to the submit member function of the queue.

Note that submitting a command group without any commands will result in an error.

2.) Define a SYCL kernel function

Define a SYCL kernel function via the single_task command within the command group, which takes only a function object which itself doesn't take any parameters.

Remember to declare a class for your kernel name in the global namespace.

3.) Stream “Hello World!” to stdout from the SYCL kernel function

Create a stream object within the command group scope as follows. The two parameters to the constructor of the stream class are the total buffer size and the statement size respectively.

Then use the stream you constructed within the SYCL kernel function to print “Hello world!” using the << operator.

4.) Try another command

Instead of single_task try another command for defining a SYCL kernel function (see SYCL 1.2.1 specification, sec 4.8.5).

Remember the function object for the parallel_for which takes a range can be an id or an item and the function object for the parallel_for which takes an nd_range must be an nd_item.

5.) Try a different dimensionality

Instead of a 1-dimensional range for your SYCL kernel function, try a 2 or 3-dimensional range.

Build And Execution Hints

For For DPC++ (using the Intel DevCloud):

dpcpp -o sycl-ex-3 -I../External/Catch2/single_include ../Code_Exercises/Exercise_3_Hello_World/source.cpp
./sycl-ex-3

For ComputeCpp:

cmake -DSYCL_ACADEMY_USE_COMPUTECPP=ON -DSYCL_ACADEMY_INSTALL_ROOT=/insert/path/to/computecpp ..
make Exercise_3_source
./Code_Exercises/Exercise_3_Hello_World/Exercise_3_source

For hipSYCL:

# Add -DHIPSYCL_GPU_ARCH=<arch> to the cmake arguments when compiling for GPUs.
# <arch> is e.g. sm_60 for NVIDIA Pascal GPUs, gfx900 for AMD Vega 56/64, and gfx906 for Radeon VII.
cmake -SYCL_ACADEMY_USE_HIPSYCL=ON -DSYCL_ACADEMY_INSTALL_ROOT=/insert/path/to/hipsycl -DHIPSYCL_PLATFORM=<cpu|cuda|rocm> ..
make Exercise_3_source
./Code_Exercises/Exercise_3_Hello_World/Exercise_3_source

Note: Printing from kernels is still experimental on ROCm, so you might get an empty output when using the hipSYCL ROCm backend. In this case, try using the CPU backend instead.