Energy efficiency is becoming an increasingly important feature for both mobile and high-performance server systems. Most processors designed today include power management features that provide processor operating points which can be used in power management algorithms. However, existing power management algorithms implicitly assume that lower performance points are more energy efficient than higher performance points. Our empirical observations indicate that for many systems, this assumption is not valid.We introduce a new concept called critical power slope to explain and capture the power-performance characteristics of systems with power management features. We evaluate three systems - a clock throttled Pentium laptop, a frequency scaled PowerPC platform, and a voltage scaled system to demonstrate the benefits of our approach. Our evaluation is based on empirical measurements of the first two systems, and publicly available data for the third. Using critical power slope, we explain why on the Pentium-based system, it is energy efficient to run only at the highest frequency, while on the PowerPC-based system, it is energy efficient to run at the lowest frequency point. We confirm our results by measuring the behavior of a web serving benchmark. Furthermore, we extend the critical power slope concept to understand the benefits of voltage scaling when combined with frequency scaling. We show that in some cases, it may be energy efficient not to reduce voltage below a certain point.

Group communication is a widely studied paradigm which is often used in building real-time and fault-tolerant distributed systems. RTCAST is a real-time group communication protocol which has been designed to work with commercial, non-real-time, off-the-shelf hardware and operating systems, such as Solaris, Linux and Windows NT. RTCAST makes probabilistic real-time guarantees based on assumptions about the performance of the underlying system. Unfortunately, the high variability of the access to system resources that these operating systems provide may limit the predictability of the real-time guarantees provided by RTCAST. By taking advantage of a service that provides resource scheduling and reservation in these operating systems, both the hardness and timing granularity of RTCAST's real-time services can be greatly improved. This paper describes an implementation of RTCAST which makes use of the Resource Kernel to provide highly predictable, real-time communication guarantees.

Java has many benefits such as security in distributed environments, reusability of code, and portability because it is architecture neutral. From those characteristics, Java is beginning to be used in many new environments. Even though Java provides various advantages, it still has problems which must be solved. One issue is that there are often real-time constraints that should be met in those applications. Current Java execution environment and language specification cannot satisfy those requirements. Our research focuses on the current limits of the Java language and its execution environment, and to seek the possibility for real-time using Java and the technologies we have available today. To investigate issues in real-time Java, we have implemented a prototype real-time Java environment which provides real-time Java threads and a real-time synchronization mechanism. Then we evaluated its performance. The results indicate that timing requirements are better met and unbounded priority inversion is avoided in our system.