A Technique for Adaptive Scheduling of Soft Real-Time Tasks

A number of multimedia and process control applications can take advantage from the ability to adapt soft real-time load to available computational capacity. This capability is required, for example, to react to changed operating conditions as well as to ensure graceful degradation of an application under transient overloads. In this paper, we illustrate a novel adaptive scheduling technique based on rate modulation of a set of periodic tasks in a range of admissible rates. By casting constraints on rate ranges in a linear programming formulation, several adaptation policies can be considered, along with additional constraints reflecting various application requirements. The paper investigates the effectiveness of rate modulation strategies both on simulated task sets and on real experiments. Partial support for this research has been provided by MURST, Italy (PRIN project ISIDE on “Dependable reactive computing systems for industrial applications” and special project “RoboCare” funded by L. 449/97), and by ASI, Agenzia Spaziale Italiana (contract I/R/134/00). Giuseppe Beccari received the Laurea degree in Electronic Engineering in 1993, and the Ph.D. in Information Technology in 1999, both from the University of Parma, Italy. In 1995 he was visiting scholar at the Technical University of Delft, Holland, and at the Laboratoire de Robotique de Paris, France. In 1999 he was employed by CSELT (Centro Studi E Laboratori Telecomunicazioni, currently TILAB, the Telecom Italia Group research center). In 2002 he moved to a spin off company involved in the EUROSAM/FSAF (Future Surface-to-Air Family self defense missile system) project. While his current professional duties focus more on software development and team coordination, dr. Beccari still enjoys investigating real-time scheduling issues and technology. Stefano Caselli received a Laurea degree in Electronic Engineering in 1982 and the Ph.D. degree in Computer and Electronic Engineering in 1987, both from the University of Bologna, Italy. In 1989-90 he has been visiting scholar at the University of Florida. From 1990 to 1999 he has held research fellow and associate professor positions at the University of Parma, Italy. He is now professor of Computer Engineering at the University of Parma, where he is also director of the Laboratory of Robotics and Intelligent Machines (RIMLab). His current research interests include development of autonomous and remotely operated robot systems, service robotics, and real-time systems. Francesco Zanichelli received a Laurea degree in Electronic Engineering in 1987 from the University of Bologna, Italy and the Ph.D. degree in Information Technologies in 1994 from the University of Parma, Italy. Since 1996 he has been an Assistant Professor with the Department of Information Engineering of the University of Parma where he is currently teaching Operating Systems, Information Systems and Multimedia Systems courses. His current research interests include distributed multimedia architectures and protocols, real-time systems, security and Quality of Service technologies for wireless networks, as well as service-oriented Grid middleware.