Providing Resource Reservations for Adaptive Applications in a Best-Effort Operating System

An important class of adaptive applications can trade off one kind of resources (e.g., network bandwidth) for requests of other resources (e.g., CPU cycles). They create new challenges for operating systems: their processor demands change rapidly based on external factors, and resource requests are recurring, though non-periodic. However these applications share some of the characteristics of "soft real-time" tasks and are often resilient with regard to un- or under-availability of resources. This paper presents a comprehensive approach to processor management for adaptive applications, the R-Scheduler. It co-exists with a best-effort scheduler and has been implemented for NetBSD and ported to Linux. The runtime costs of admission control and scheduling are modest (below 1%). For realistic usage scenarios, the R-Scheduler allows the application to meet its time limits, whereas the traditional (default) best-effort scheduling discipline fails to allocate the CPU resources effectively.