[mpich-discuss] Can I choose between MPI_WIN_UNIFIED and MPI_WIN_SEPARATE ?

Hey, Can I choose between the two memory models, or is this provided by the mpi implementation or underlying hardware? If I can choose: How can I? If I cannot choose: Why is that? I tried using MPI_Win_set_attr to set it, but Mpich throws an error that the key is invalid. (I am using mpich 3.0.4) Reading the standard I couldn't find out wether this is supposed to be choosable by the user. I just assumed it is. Because, if I don't query MPI_WIN_MODEL, there is a chance my program works on one but not on the other. So I have a correct program depending on which model there is and the code looks exactly the same. Which is behavior I would not expect. I hope you can help, cheers, Ronny