Performance Analysis Of All-to-All Communication on the Blue Gene/L Supercomputer

All-to-all communication is a well known performance bottleneck for many applications. For such applications to scale to a large number of processors, optimizing all-to-all communication is critical. In this paper, we analyze the performance of all-to-all communication on the Blue Gene/L torus interconnection network, which has limited bisection bandwidth. The torus interconnect topology has link contention even for all-to-all communication operations with short messages. We observed that the performance of all-to-all communication also depends on the shape of the processor partition. We present a performance analysis of all-to-all communication on mesh and torus partitions of various shapes and sizes. We then present optimization schemes to enhance the performance of all-to-all communication. The large message optimization substantially improves all-to-all performance on an asymmetric torus. In particular, performance improved from about 70% to over 99% of peak on a 20,480 (40 × 32 × 16) node configuration, which was the largest machine to which we had access. The short message optimization can double all-to-all performance for very short messages.

By: Sameer Kumar; Philip Heidelberger

Published in: RC24327 in 2007


This Research Report is available. This report has been submitted for publication outside of IBM and will probably be copyrighted if accepted for publication. It has been issued as a Research Report for early dissemination of its contents. In view of the transfer of copyright to the outside publisher, its distribution outside of IBM prior to publication should be limited to peer communications and specific requests. After outside publication, requests should be filled only by reprints or legally obtained copies of the article (e.g., payment of royalties). I have read and understand this notice and am a member of the scientific community outside or inside of IBM seeking a single copy only.


Questions about this service can be mailed to .