  Network congestion in high-speed interconnects is a major source of
application run time performance variation. Recent years have witnessed a surge
of interest from both academia and industry in the development of novel
approaches for congestion control at the network level and in application
placement, mapping, and scheduling at the system-level. However, these studies
are based on proxy applications and benchmarks that are not representative of
field-congestion characteristics of high-speed interconnects. To address this
gap, we present (a) an end-to-end framework for monitoring and analysis to
support long-term field-congestion characterization studies, and (b) an
empirical study of network congestion in petascale systems across two different
interconnect technologies: (i) Cray Gemini, which uses a 3-D torus topology,
and (ii) Cray Aries, which uses the DragonFly topology.
