two-face collective scenario (fwd)
Rolf Rabenseifner (Rabenseifner@RUS.Uni-Stuttgart.DE)
Fri, 31 Jan 1997 17:00:54 +0100 (MEZ)
(Sorry I have sent it to external instead of collective.)
An application scenario from real programmers life -- a background
information for the two-faced collective proposal.
Forwarded message:
> From: Thomas Boenisch <Thomas.Boenisch@rus.uni-stuttgart.de>
>
> Hallo Rolf,
>
> I need a incomplite reduce and allreduce to hide communication time
> and to avoid synchronisation in my application:
>
> One Iteration (programmed with your proposed two-faced...):
>
> call MPI_REDUCE_START(teilresl2, resl2, 1, REALx, MPI_SUM, 0,
> . MPI_COMM_WORLD, info)
> call MPI_ALLREDUCE_START(teilresl1, resl1, 1, REALx, MPI_SUM,
> . mpi_comm_world_a, info)
> call MPI_ALLREDUCE_START(teilresl0, resl0, 1, REALx, MPI_MAX,
> . mpi_comm_world_b, info)
>
> c...solv the equationsystem
> call parallelsolver( rm000, rmf00, rmb00, rm0f0, rm0b0, rm00f,
> . rm00b, dq, rhs, nsubit, nhofhausit )
>
> c...computation of the CFL-Number with resl1
> call MPI_ALLREDUCE_END(mpi_comm_world_a, resl1)
> ...
>
> c...output of all residuals
> call MPI_REDUCE_END(MPI_COMM_WORLD, resl2)
> call MPI_ALLREDUCE_END(mpi_comm_world_b, resl0)
> ...
>
> Ciao
> Thomas
This means that parts of the program (here the parallelsolver)
can be overlayed with the effort for three reduce operations.
Rolf
Rolf Rabenseifner (Computer Center )
Rechenzentrum Universitaet Stuttgart (University of Stuttgart)
Allmandring 30 Phone: ++49 711 6855530
D-70550 Stuttgart 80 FAX: ++49 711 6787626
Germany rabenseifner@rus.uni-stuttgart.de