Rate-Based Resource Allocation Models for Embedded Systems

Run-time executives and operating system kernels for embedded systems have long relied exclusively on static priority scheduling of tasks to ensure timing constraints and other correctness conditions are met. Static priority scheduling is easy to understand and support but it suffers from a number of significant shortcomings such as the complexity of simultaneously mapping timing and importance constraints onto priority values. Rate-based resource allocation schemes offer an attractive alternative to traditional static priority scheduling as they offer flexibility in specifying and managing timing and criticality constraints. This paper presents a taxonomy of rate-based resource allocation and summarizes the results of some recent experiments evaluating the real-time performance of three allocation schemes for a suite of intra-kernel and application-level scheduling problems encountered in supporting a multimedia workload on FreeBSD UNIX.