Fine-Grain Adaptive Scheduling using Feedback

We describe an implementation of a fine-grain adaptive scheduling mechanism, based on software feedback. Conventional scheduling makes job assignment exclusively a function of time. We broaden the meaning of the term "scheduling" to include job assignment as a function of a sequence of events, such as timer interrupts, I/O operations, queue overflodunderflow, and system call traps. Our implementation of software feedback in the Synthesis operating system is analogous to the hardware phase locked loop. Very low overhead context switches and scheduling cost (a few microseconds on a 68020-based machine) makes this implementation useful to practical applications such as digital signal processing. Since scheduling actions and policy adjustments occur at very frne granularity (sub-millisecond intervals), Synthesis adaptive scheduling is very sensitive. Interesting applications of fine-grain adaptive scheduling include I/O device management, real-time scheduling, and distributed adaptive scheduling. @ Computing Systems, Vol. 3'No. I 'Winter 1990 L39