Difference between global and device functions

Question

Can anyone describe the differences between __global__ and __device__ ?

When should I use __device__, and when to use __glob

Answer 1

Global functions are also called "kernels". It's the functions that you may call from the host side using CUDA kernel call semantics (<<<...>>>).

Device functions can only be called from other device or global functions. __device__ functions cannot be called from host code.