Fri May 29 06:56:33 UTC 2020

test phlog post 1

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Network  contention frequently dominates the run time of parallel
algorithms and limits scaling performance. Most previous  studies
mitigate  or eliminate contention by utilizing one of several ap-
proaches: communication-minimizing  algorithms;  hotspot-avoiding
routing schemes; topology-aware task mapping; or improving global
network properties, such as bisection bandwidth,  edge-expansion,
partitioning,  and  network  diameter. In practice, parallel jobs
often use only a fraction of a host system. How do processor  al-
location  policies  affect contention within a partition? We uti-
lize edge-isoperimetric analysis of network graphs  to  determine
whether  a  network partition has optimal internal bisection. In-
creasing the bisection allows a more efficient use of the network
resources,  decreasing  or  completely  eliminating the link con-
tention. We first study torus networks and characterize partition
geometries that maximize internal bisection bandwidth. We examine
the allocation policies of Mira and JUQUEEN, the two largest pub-
licly-accessible  Blue  Gene/Q  torus-based  supercomputers.  Our
analysis demonstrates that the bisection bandwidth of their  cur-
rent partitions can often be improved by changing the partitions'
geometries. These can yield up to a X2  speedup  for  contention-
bound  workloads.  Benchmarking  experiments validate the predic-
tions. Our analysis applies to allocation policies of other  net-
works.