Section: New Software and Platforms

Hsplit

Hardware communicators split

Keywords: MPI communication - Topology - Hardware platform

Scientific Description: Hsplit is a library that implements an abstraction allowing the programmer using MPI in their parallel applications to access the underlying hardware structure through a hierarchy of communicators. Hsplit is based on the MPI_Comm_split_type routine and provides a new value for the split_type argument that specifically creates a hierarchy a subcommunicators where each new subcommunicator corresponds to a meaningful hardware level. The important point is that only the structure o the hardware is exploited and the number of levels or the levels names are not fixed so as to propose a solution independent from future hardware evolutions (such as new levels for instance). Another flavor of this MPI_Comm_split_type function is provided that creates a roots communicators at the same time a subcommunicator is produced, in order to ease the collective communication and/or synchronization among subcommunicators.

Functional Description: Hsplit implements an abstraction that allows the programmer using MPI in their parallel applications to access the underlying hardware structure through a hierarchy of communicators. Hsplit is based on the MPI_Comm_split_type routine and provides a new value for the split_type argument that specifically creates a hierarchy a subcommunicators where each new subcommunicator corresponds to a meaningful hardware level. The important point is that only the structure o the hardware is exploited and the number of levels or the levels names are not fixed so as to propose a solution independent from future hardware evolutions (such as new levels for instance). Another flavor of this MPI_Comm_split_type function is provided that creates a roots communicators at the same time a subcommunicator is produced, in order to ease the collective communication and/or synchronization among subcommunicators.

News Of The Year: Most of our proposal had been officially read in front of the MPI Forum at the last physical meeting in December at Albuquerque. This concerns hte guided and the unguided mode of the split function. This now has to pass two votes in the next physical meetings in 2020 to be part of the new version of the standard: MPI 4.0 that shall be ratified and released at the end of 2020. Since no other MPI library currently implements the unguided mode, Hsplit will be the only sofware that is currently able to provide it.

• Participants: Guillaume Mercier, Brice Goglin and Emmanuel Jeannot

• Contact: Guillaume Mercier

• Publications: A hierarchical model to manage hardware topology in MPI applications - A Hierarchical Model to Manage Hardware Topology in MPI Applications

• URL: http://mpi-topology.gforge.inria.fr/