On the Shadow Cpu Approximation for Modelling Priority Scheduling in Computer Systems (Classic Reprint)

Excerpt from On the Shadow Cpu Approximation for Modelling Priority Scheduling in Computer Systems A sound performance evaluation methodology is essential to the design and use of computer systems. Among performance evaluation methods, queuing network models have been widely recognized as cost and time effective tools, capable of predicting ability and necessary complements of simulations. Algorithms for efficiently estimating the throughput, response time and other measures of performance have been devised for a broad range of queuing network models. Although this range is very rich and adequate for modelling many realistic features of a computer system, nevertheless it has major limitations. An important one is the inability to model pre-emptive priority scheduling disciplines. Although exact closed-form solutions for such network models are open research problems, several approximation techniques have been proposed. An important one was Sevcik's [Sevc, 77] "shadow CPU" technique, which admits a product form solution and gives performance bounds which are quite tight in many circumstances. In this paper, we extend the shadow CPU model to an optimal approximation of the priority model, within the restrictions of the product form. We propose a computationally efficient sub-optimal approximation technique which gives tighter performance bounds compared to the original shadow CPU technique. We also investigate the limitations of such shadow server-product form techniques for modelling priorities. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.