Scheduling in parallel systems with a hierarchical organization of tasks

To exploit multiple processors, a job is usually partitioned into several tasks that can be executed concurrently. These tasks wait for processors in task ready queue(s). There are two basic ways in which waiting ready tasks can be organized: centralized organization or distributed organization. In a centralized organization, a single central task queue is maintained. In the latter case, each processor has its own private ready queue of tasks. Ideally, a central ready queue global to all processors is desired over the distributed organization. However, the centralized organization is not suitable for large parallel systems because the global task queue could become a bottleneck. A hierarchical organization has been proposed to incorporate the good features of these two organizations. This paper studies the impact of job and task scheduling policies on the performance of the hierarchical organization.