Dynamic control of parallelism and granularity in executing nested parallel loops

The effects of controlling granularity and the growth of parallelism at runtime in executing automatically parallelized programs are addressed. The authors version-switch method allows the runtime system to dynamically choose the appropriate version of codes for execution in order to achieve better performance. The decision when to switch version is shown to be critical to the effectiveness of the method. A framework is built to study how to estimate the current work load for deciding when to switch versions. Four different control schemes based on local or global estimation of workload have been implemented in the runtime system. Their results are compared and discussed in detail