The continuous display of information derived from on-line monitoring presents problems that are more difficult to resolve than those associated with off-line displays. Handling these problems requires a systematic approach affecting both the displays and the monitoring system itself. This paper discusses the problems inherent in on-line display and the approach to them taken by the Falcon monitoring system. Keywords: online displays, parallel programs 1 Introduction In order to support monitoring and interactive steering of computer programs during execution, program users need accurate and easy-tounderstand program information. Graphical displays have been shown useful in presenting data structures, algorithms, runtime program behavior, and performance information to human users. Most of the research on graphical displays has focused on the offline presentation of information, however. For users to interactively steer running programs, mechanisms are needed to handle the continuous...

. Understanding the dynamic behavior of parallel programs is a critical issue both for debugging and for optimization. A visualization tool displaying an animated sequence of the global states the program runs through offers valuable support for this process. The paper presents the features and the implementation of VISTOP, a state based visualizer for PVM applications. It supports program flow visualization based on various views and uses an event ordering algorithm to ensure consistent visualization without requiring a global clock. 1 Introduction The complex interaction of a large number of components makes programming parallel and distributed systems a complicated and error-prone task. The dynamics supported by programming libraries like PVM can make this situation even worse, because the execution of programs where tasks (or other objects) are created and deleted during runtime can be hard to comprehend. Breakpoint-based debuggers, which are also available for parallel programs n...

We introduce a new performance metric, called Load Balancing Factor (LBF), to assist programmers with evaluating different tuning alternatives. The LBF metric differs from traditional performance metrics since it is intended to measure the performance implications of a specific tuning alternative rather than quantifying where time is spent in the current version of the program. A second unique aspect of the metric is that it provides guidance about moving work within a distributed or parallel program rather than reducing it. A variation of the LBF metric can also be used to predict the performance impact of changing the underlying network. The LBF metric can be computed incrementally and online during the execution of the program to be tuned. We also present a case study that shows that our metric can predict the actual performance gains accurately for a test suite of six programs. 1. Introduction To successfully tune a distributed or parallel program, the cause of a performance bottl...

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