Efficient Work Stealing for Portability of Nested Parallelism and Composability of Multithreaded Program

We present performance evaluations of parallel-for loop with work stealing technique. The parallel-for by work stealing transforms the parallel-loop into a form of binary tree by making use of method of divide-and-conquer. Iterations are distributed in the leaves procedures of the binary tree, and the parallel executions are performed by stealing subtrees from the bottom of the tree. The work stealing and divide-and-conquer are used to address the portability problem in nested parallelism and composability. By work stealing and divide-and-conquer techniques, fine-grained parallel-for can be implemented without contributing large work overhead. Low work overhead is important as the number of processor could be less than expected. Low overhead and fine-grained of work stealing scheduler makes highly parallel processor cores are able to scale the performance. In addition, the approach used in this work makes efficient nested parallelism is possible. Because of a low overhead, we show that the work stealing and divide-and-conquer deliver good scalability in nested parallel Sparse LU factorization.