On Tue, Mar 30, 2010 at 11:51:39PM +0100, Ricardo Reis wrote: > > If using the master/slace IO model, would it be better to cicle > through all the process and each one would write it's part of the > array into the file. This file would be open in "stream" mode... > > like > > do p=0,nprocs-1 > > if(my_rank.eq.i)then > > openfile (append mode) > write_to_file > closefile > > endif > > call MPI_Barrier(world,ierr) > > enddo
Note that there's no guarantee of the order here, though. Nothing prevents rank 30 from hitting that loop before rank 2 does. To ensure order, you could MPI_SEND a token around a ring of MPI processes. Yuck. One approach might be to use MPI_SCAN to collect offsets (the amount of data each process will write) and then do an MPI_FILE_WRITE_AT_ALL. If you are stuck with NFS, then yes, send to master. ==rob -- Rob Latham Mathematics and Computer Science Division Argonne National Lab, IL USA
