[NEST Users] Question about MPI and multithreading

Dear all, I am actually working on the I/O for Nest with MPI. I am not aware of the solution of Nest for managing the communication between process and thread. I would like to learn more about it for adapting the interface with the actual solution. If someone can answer some of my questions : 1) By looking at the initialization of the MPI, I saw Nest use the /MPI_THREAD_FUNNELED /for the level of thread support. What is the reason for it? 2) This level of thread support surprise me because I suppose that it will overload one thread with all the MPI calls. Why do you do not choose the level /MPI_THREAD_SERIALIZED/? 3) I would like to have different levels for thread support. Do you think it's possible ? Thank you in advance for your answer, Kusch Lionel PS: The reference to the different MPI thread support : http://mpi.deino.net/mpi_functions/MPI_Init_thread.html