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GPU
,→The Implicitly Parallel SIMT Programming Model
=The Implicitly Parallel SIMT Programming Model=
CUDA, OpenCL, ROCm HIP, and even other GPU languages like GLSL, HLSL, C++AMP and even non-GPU languages like Intel [https://ispc.github.io/ ISPC] all have the same model of implicitly parallel programming. All threads are given an identifier: a threadIdx in CUDA or local_id in OpenCL. Aside from this index, all threads of a kernel will execute the same code.
The smallest group of threads is called a CUDA Warp, or OpenCL Wavefront. NVidia GPUs execute 32-threads per warp, while AMD GCN GPUs execute 64-threads per wavefront. All threads within a Warp or Wavefront share an instruction pointer. Consider the following CUDA code:
