Effective reuse of coupling technologies for Earth System Models

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Dunlap, Ralph S.
Rugaber, Spencer
Mark, Leo
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Designing and implementing coupled Earth System Models (ESMs) is a challenge for climate scientists and software engineers alike. Coupled models incorporate two or more independent numerical models into a single application, allowing for the simulation of complex feedback effects. As ESMs increase in sophistication, incorporating higher fidelity models of geophysical processes, developers are faced with the issue of managing increasing software complexity. Recently, reusable coupling software has emerged to aid developers in building coupled models. Effective reuse of coupling infrastructure means increasing the number of coupling functions reused, minimizing code duplication, reducing the development time required to couple models, and enabling flexible composition of coupling infrastructure with existing constituent model implementations. Despite the widespread availability of software packages that provide coupling infrastructure, effective reuse of coupling technologies remains an elusive goal: coupling models is effort-intensive, often requiring weeks or months of developer time to work through implementation details, even when starting from a set of existing software components. Coupling technologies are never used in isolation: they must be integrated with multiple existing constituent models to provide their primary services, such as model-to-model data communication and transformation. Unfortunately, the high level of interdependence between coupling concerns and scientific concerns has resulted in high interdependence between the infrastructure code and the scientific code within a model’s implementation. These dependencies are a source of complexity which tends to reduce reusability of coupling infrastructure. This dissertation presents mechanisms for increasing modeler productivity based on improving reuse of coupling infrastructure and raising the level of abstraction at which modelers work. This dissertation argues that effective reuse of coupling technologies can be achieved by decomposing existing coupling technologies into a salient set of implementation-independent features required for coupling high-performance models, increasing abstraction levels at which model developers work, and facilitating integration of coupling infrastructure with constituent models via component-based modularization of coupling features. The contributions of this research include: (1) a comprehensive feature model that identifies the multi-dimensional design space of coupling technologies used in high-performance Earth System Models, (2) Cupid, a domain-specific language and compiler for specifying coupling configurations declaratively and generating their implementations automatically, and (3) Component-based Coupling Operators (CC-Ops), a modular approach to code reuse of coupling infrastructure based on component technologies for high-performance scientific settings. The Cupid domain-specific language is evaluated by specifying a coupling configuration for an example fluid dynamics model and measuring the amount of code generated by the Cupid compiler compared to a hand coded version. The CC-Op approach is evaluated by implementing several CC-Ops using an existing high-performance component framework and measuring performance in terms of scalability and overhead.
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