TASK GEOMETRY FOR COMMODITY LINUX CLUSTERS AND GRIDS: A SOLUTION FOR TOPOLOGY-AWARE LOAD BALANCING OF SYNCHRONOUSLY COUPLED, ASYMMETRIC ATMOSPHERIC MODELS

State-of-the-art atmospheric models comprise multiple components that interact synchronously. Because some components need to expend more computational effort than others, it is often the case that these components are computationally imbalanced. Although parallelism within a component can reduce the imbalance, there is still a need to coordinate component interaction via a coupler in real time. To address this issue, NCAR identified requirements for Task Geometry — a construct that specifies for the purpose of coordination the run-time topology within and between components. Although it has recently become generically available in Platform LSF HPC, the current focus is commodity architectures based on the Linux operating environment. Crafted originally for CCSM, Task Geometry appears applicable to other systems-coupled atmospheric models such as 4D-Var. Scale-coupled atmospheric models also show promise for application in areas such as subgrid-scale parameterizations for GCM models, and the class of interactions demanded by use cases emerging in the area of Homeland Security. In all cases it is possible to demonstrate via speedup and efficiency that Task Geometry enhances performance, however both metrics are problematical to quantify except in simple cases. With applicability from isolated Linux clusters to grids, Task Geometry remains useful in contexts that span organizational and/or geographic boundaries.