Parallel Performance Visualization Method
Essentially, Kiviat Figures are histograms arranged in a circular shape. Like a histogram, a Kiviat figure displays single magnitudes for each of a series of categories. The categories, however, are arranged like spokes in a wheel.
Example of Kiviat figures for eight categories of data. At each category axis (0-7) the displayed value is given by the intersection of the inner (dark green) region with the category axis. When the inner region protrudes to the rim, the category has a large value.
The intersection point of the central polygon with a category spoke provides the corresponding category magnitude. An intersection close to the rim indicates a large magnitude; close to the core indicates a small magnitude. Consequently, a glance at the "shape" of a Kiviat figure ("big," "small," "squished," "round," etc.) can quickly convey a great deal of information about the underlying metrics.
Like histograms, Kiviat figures are useful for providing summary data. The diagrams above might, for example, represent total utilization for each of eight processors. Typically, the rim would represent 100% utilization (processor was busy during the entire program execution).
Note that for a simple Kiviat diagram (as in the Figure), resolution (i.e.,, number of categories that can be separately represented) is limited by pixel resolution, and diameter of the figure at the represented value. That is, resolution is poorer nearer to the figure center. This finite resolution can limit the number of categories (e.g., processors) a Kiviat figure can accurately display.
Kiviat figures like those above usually represent a static picture; that is, they do not have a "time axis." They represent either an instantaneous state (a "snapshot") or a time-integrated state (a summary). This can be a disadvantage in tuning; to find the source of a performance problem, you often need to find the time (or segment of source code) where a problem arose. This need has motivated two interesting time-dependent Kiviat-based displays.
The first is animation; a display can show a "movie" in which each frame is a Kiviat figure of an instantaneous state. ParaGraph uses animated Kiviat figures to display processor utilization as a function of time.
The second approach is to use a 3D rendering system to create a Kiviat Tube. Consider a sequence of Kiviat figures, computed at regular time intervals. Now, imagine that the sequence of figures is stacked in order along a central axis, so that each figure is a separate cross section of a three-dimensional tube. What you get is called a Kiviat tube. The shape of the tube, viewed in an orthographic rendering, reveals the time dependence of each of the displayed categories. Hackstadt and Maloney (available on the web, follow links below) and Heath, Maloney and Rover (Related Publications) provide example sets Kiviat tube figures, displaying processor utilization as a function of time.
Related Publications:
Related Methods/Techniques:
Related Tools/Applications:
This page revised Tue Oct 27 15:17:37 PDT 1998
Comments and suggestions to:
pancake@cs.orst.edu