In this first exercise you will learn:
- How to manage data using buffers.
- How to access data using accessors.
- How to define an nd range SYCL kernel function.
In SYCL buffers are used to manage data across the host and device(s), and accessors are used to declare data dependencies to a SYCL kernel function as well as to access the data within a SYCL kernel function.
1.) Allocate your input and output vectors
Allocate memory on the host for your input and output data using std::vectors and initialize the input with values.
2.) Construct buffers
Construct a buffer to manage your input and output data. The template parameters for the the buffer class are the type and then the dimensionality. The parameters to construct a buffer are a pointer to the host data and a range.
Remember the dimensionality of the range must match the dimensionality of the buffer.
3.) Construct accessors
Construct an accessor for your input and output buffers. The template parameter to get_access is the access mode that specifies how you wish to use the data managed by the buffer.
Remember to pass the handler to get_access, if you don't this will construct a host accessor, which behaves differently to a regular accessor.
4.) Declare your kernel
Declare a SYCL kernel function using the parallel_for command with a range matching the size of the std::vectors. The kernel function should use the operator[] of the accessor objects to read from the inputs and write the sum to the output.
Remember the accessor's operator[] can take either a size_t (when the dimensionality is 1) and an id.
5.) Try a temporary buffer
You can construct a temporary buffer that doesn't copy back on destruction by initialising it with just a range and no host pointer.