Open MPI's point-to-point communications abstractions, described in this paper, handle several different communications scenarios, with a portable, high-performance design and implementation. These abstractions support two types of low-level communication protocols – general purpose point-to-point communications, like the OpenIB interface, and MPI-like interfaces, such as Myricom's MX library. Support for the first type of protocols makes use of all communications resources available to a given application run, with optional support for communications error recovery. The latter provides a interface layer, relying on the communications library to guarantee correct MPI message ordering and matching. This paper describes the three point-to-point communications protocols currently supported in the Open MPI implementation, supported with performance data. This includes comparisons with other MPI implementations using the OpenIB, MX, and GM communications libraries.
