With the rapidly increasing diversity of parallel architectures and the increasing time and labor for developing parallel applications, the performance portability of parallel programs is becoming increasingly important and should be considered when designing parallel execution models, APIs, and runtime system software. This paper analyzes both code portability and performance portability of parallel programs based on the EARTH model -- an event-driven fine-grain multi-threaded execution and architecture model. We discuss several design considerations of the EARTH system that contribute to the performance portability of parallel applications. Experiments of four representative benchmarks are conducted on several different parallel architectures, including two clusters listed in the 23rd supercomputer TOP500 list. The results demonstrate that EARTH based programs can achieve robust performance portability across the selected hardware platforms without any code modification or tuning.