Computer Science Department
School of Computer Science, Carnegie Mellon University


Resource Signal Prediction and Its Application to Real-time Scheduling Advisors

Peter August Dinda

May 2000

Ph.D. Thesis

Keywords: Performance prediction, resource signal prediction, time series analysis, distributed real-time systems, distributed systems, distributed interactive applications

A distributed interactive application spawns resilient real-time tasks with known resource requirements in response to aperiodic user actions. When running in a shared computing environment that supports neither reservations nor globally-respected priorities, such an application must carefully choose which host runs a task in order to increase the chances that the task's deadline will be met.

A real-time scheduling advisor is a middleware service that the application can use to find the most appropriate host for the task. In addition to recommending a host, the advisor also predicts the running time of the task on that host. The application uses this feedback to modify the task's resource requirements or deadline until a host is found where the task will meet its deadline with sufficiently high probability.

This dissertation recommends basing real-time scheduling advisors on the explicit prediction of resource signals, which are easily measured, time-varying, scalar quantities that are strongly correlated with resource availability. This resource-oriented approach has numerous advantages over the competing application-oriented approach, which I also studied. It scales well, makes decisions based on up-to-date information, can support other forms of adaptation advisors, and can easily leverage advances in statistical signal prediction techniques. However, resource signal predictions exist at considerable remove from predictions of application performance.

To show that this gap can be spanned, this dissertation describes the design, implementation, and performance evaluation of a prototype real-time scheduling advisor that is based on the prediction of host load signals. I have found that, despite its complex properties, which include self-similarity and epochal behavior, host load can be usefully predicted using linear time series models. These models have sufficiently low overhead to be used in practice, and I have developed a toolkit to make it easy to do so. Furthermore, I have devised an algorithm that uses host load predictions to compute a confidence interval for the running time of a task on a particular host. My real-time scheduling advisor uses these confidence intervals to provide useful recommendations to applications. Each layer of this online system has been evaluated using real host load signals and workloads.

Being able to predict the running time of a task is vital to controlling many different adaptation mechanisms in pursuit of goals other than simply those of the real-time scheduling advisor. For this reason, I also expose the running time advisor, the part of my system that computes a confidence interval for the running time of a task.

158 pages

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