A parallel programming system implements dynamic load balancing to distribute processing workload to available processors in a parallel computer. A preprocessor in the system converts a nested parallel program into sequential code executable on processors of the parallel computer and calls to a message passing interface for inter-processor communication among the processors. When processing a nested parallel program, the preprocessor inserts a test function to evaluate the computational cost of a function call. At runtime, processors evaluate the test function to determine whether to ship a function call to another processor. This approach enables processors to offload function calls to other available processors in cases where it is more efficient to incur the cost of shipping the function call and receiving the results than it is to process the function call on the original processor.