Terminology
In this chapter, OpenMP and SYCL terminology is used interchangeably
to describe the partitioning of iterations of an offloaded parallel
loop.
As described in the “SYCL Thread Hierarchy and Mapping” chapter, the
iterations of a parallel loop (execution range) offloaded onto the GPU
are divided into work-groups, sub-groups, and work-items. The ND-range
represents the total execution range, which is divided into
work-groups of equal size. A work-group is a 1-, 2-, or 3-dimensional
set of work-items. Each work-group can be divided into sub-groups. A
sub-group represents a short range of consecutive work-items that are
processed together as a SIMD vector.
The following table shows how SYCL concepts map to OpenMP and CUDA
concepts.
SYCL | OpenMP | CUDA |
|---|---|---|
Work-item | OpenMP thread
or SIMD lane | CUDA thread |
Work-group | Team | Thread block |
Work-group size | Team size | Thread block size |
Number of work-groups | Number of teams | Number of thread blocks |
Sub-group | SIMD chunk
( simdlen = 8, 16, 32) | Warp (size = 32) |
Maximum number of
work-items per
work-group | Thread limit | Maximum number of
of CUDA threads per
thread block |