MPI vs openMP for a shared memory
mpi, openmp, shared-memory
Solution
With most distributed memory platforms nowadays consisting of SMP or NUMA nodes it just makes no sense to not use OpenMP. OpenMP and MPI can perfectly work together; OpenMP feeds the cores on each node and MPI communicates between the nodes. This is called hybrid programming. It was considered exotic 10 years ago but now it is becoming mainstream in High Performance Computing.
As for the question itself, the right answer, given the information provided, has always been one and the same: IT DEPENDS.
Problem
Lets say there is a computer with 4 CPUs each having 2 cores, so totally 8 cores. With my limited understanding I think that all processors share same memory in this case. Now, is it better to directly use openMP or to use MPI to make it general so that the code could work on both distributed and shared settings. Also, if I use MPI for a shared setting would performance decrease compared with openMP?