Radar charts allow a good way to compare elements of a dimension in a function of several metrics. This make them useful for seeing which variable have similar values or if there are any outlier amongst each variable. Radar charts are also useful for seeing which variables are scoring high or low within a dataset, making them ideal for displaying performance.
Radar chart is also called Spider, Star or Web chart. It is a two-dimensional chart type which is used to show, in a graphical way, series of values over many variables. Radar chart uses an axis for each variable that are arranged radially around a central point, with equal distances between each other. Lines that connected adjacent variables from axis to axis create a polygonal shape that is filled with a color.
In this post we show how Radar chart works on Cycles per Instruction Breakdown (CPI breakdown) plug-in which is part of IBM Software Development Kit for Linux on Power (SDK). First we introduce CPI Breakdown plug-in and then we explain CPI radar chart.
2. CPI Breakdown Plug-in
CPI (cycles per instruction) analysis was designed aiming to improve application performance, it refers to how many processor cycles are needed to complete an instruction. An instruction can be a read/write from memory operation, an arithmetic calculation, or bit-wise operation. The more cycles the processor takes to complete an instruction, the poorer the performance of the application in the processor.
In the CPI breakdown model, a set of processor events is broken down into components. Processor performance counters calculate metrics for the event components. This approach provides a complete view of how the application behaves concerning processor performance.
The CPI breakdown plug-in shows five tabs called: CPI Breakdown Model, CPI Radar Chart, Metrics View, Events View and Drilldown View. It collects several required events, and then calculates metrics for the CPI breakdown model. For more information about events and metrics please see User guide.
3. CPI Radar Chart
CPI breakdown plug-in also creates a cpi file for each execution (profiling) which can be used to recovery info about events and metric every time we want. The cpi file is basically a xml file that contains every data about events and metrics from CPI Breakdown model.
In order to compare cpi files content, we introduce CPI Radar Chart which at first use only events to compare. It shows events from Breakdown 2 when we use Power 8 machine and Events from Breakdown 3 in Power 7 case. The radar graphics shows hot spots events and put them near to most external circle, as shown in Figure 1.
Figure 1: CPI Radar Chart with a single data series.
During the creation of the CPI Radar Chart it is first executed the sorting of the events and then a name verification is executed in order to perform a comparison as shown in the Figure 2.
Figure 2: CPI Radar Charts comparison
Finally, because simplicity of shapes used by Radar Chart it is very helpful to evaluate and visualize data from CPI Breakdown model. CPI Radar Chart allow us comparison between CPI profilings in a simple and friendly way.