"Kirk, Benjamin (JSC-EG311)" <benjamin.k...@nasa.gov> writes:
> MPI_Win_create (&recv_buf[0], recv_buf.size()*sizeof(unsigned int), > sizeof(unsigned int), > MPI_INFO_NULL, MPI_COMM_WORLD, > &win); In practice, this is implemented using something like an MPI_Allreduce with 3*int*comm_size data. > for (unsigned int proc=0; proc<numprocs; proc++) > MPI_Put (&procid, 1, MPI_UNSIGNED, > proc, procid, 1, MPI_UNSIGNED, > win); > > MPI_Win_fence (0, win); If you don't send to all the comms, how will the receiver know which slots have been written to? Or is your idea to initialize with known-invalid data and then scan through it to find the now-valid data? Given the quite high cost of creating the window, I think you're definitely better off using MPI_Reduce_scatter from MPI-2 (or the MPI-3 nonblocking consensus algorithm implemented in PetscCommBuildTwoSided) to determine who you need to receive from, then using point-to-point. If you have the window and rendezvous worked out, one-sided can be faster on some hardware, but point-to-point is still very good and it's not going to be your bottleneck if it's used well.
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