Architecture and Performance of the BlueGene/L Message Layer

The BlueGene/L supercomputer is planned to consist of 65,536 dual-processor compute nodes interconnected by high speed torus and tree networks. Compute nodes can only address local memory, making message passing the natural programming model for the machine. In this paper we present the architecture and performance of the BlueGene/L message layer, the software library that makes an efficient MPI implementation possible. We describe the components and protocols of the message layer, and present microbenchmark based performance results for several aspects of the library.