When building mpich for a heterogeneous collection of workstations, you may want to configure with the option -no_short_longs. This indicates to mpich that it should not provide support for the C type long double. This can improve performance between systems that have the same datatype lengths for all other types (some Intel x86 machines have 12 byte (80 bits) long doubles; many other systems use either 8 or 16 byte long doubles).