HLS: a framework for composing soft real-time schedulers

Hierarchical CPU scheduling has emerged as a way to (1) support applications with diverse scheduling requirements in open systems, and (2) provide load isolation between applications, users, and other resource principals. Most existing work on hierarchical scheduling has focused on systems that provide a fixed scheduling model: the schedulers in part or all of the hierarchy are specified in advance. In this paper we describe a system of guarantees that permits a general hierarchy of soft real-time schedulers one that contains arbitrary scheduling algorithms at all points within the hierarchy - to be analyzed. This analysis results in deterministic guarantees for threads at the leaves of the hierarchy. We also describe the design, implementation, and performance evaluation of a system for supporting such a hierarchy in the Windows 2000 kernel. Finally, we show that complex scheduling behaviors can be created using small schedulers as components and describe the HLS programming environment.