UPC Collectives Library 2.0

Collective communication has been a part of the UPC standard since having been introduced in 2005 with the UPC Specification version 1.2. However, unlike MPI collectives, UPC collectives have never caught on and are rarely used. In this paper we identify and discuss several fundamental limitations and important missing features in the design of the existing UPC collectives that make them inconvenient to use and unsuitable for performance optimization. Next, we propose a new, consistent, portable and high performance collectives library that is aimed to augment UPC with a full complement of the collectives used by MPI. Ours is a pure library based approach; we change none of the functions in the existing UPC specification. We discuss the implementation requirements for this new UPC collectives library, and how our design attempts to minimize the implementation effort by enabling the reuse of existing collective implementations.