Client and Host Attributes

Editor's note: This is an entirely new section - it has not been voted on yet.

This section is heavily influenced by Section 5.3 of the MPI 2 Journal of Development [1], ``Cluster Attributes.''

Inter-client and inter-host communications may be significantly slower than communications between processes on the same host. It is therefore desirable for programs to be able to determine which ranks are local and which are remote.

The following attributes are defined on all communicators:

MPI_CLIENT_SIZE

returns as the keyvalue the number of IMPI clients included in the communicator.

MPI_CLIENT_COLOR

returns as the keyvalue a number between 0 and MPI_CLIENT_SIZE-1. IMPI processes that are represented by the same client return the same value. IMPI processes that are represented by different clients return different values.

MPI_HOST_SIZE

returns as the keyvalue the number of IMPI hosts inlcuded in the communicator.

MPI_HOST_COLOR

returns as the keyvalue a number between 0 and MPI_HOST_SIZE-1. IMPI processes that are represented by the same host return the same value. IMPI processes that are represented by different hosts return different values.

Advice to users.This interface returns no information about the significance of the difference between the communication inside and between client/hosts members. However, this can be achieved by small application-specific benchmarks as part of the application. The returned color can be used as input to MPI_COMM_SPLIT.(End of advice to users.)