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CPE 619 The Art of Data Presentation

CPE 619 The Art of Data Presentation. Aleksandar Milenković The LaCASA Laboratory Electrical and Computer Engineering Department The University of Alabama in Huntsville http://www.ece.uah.edu/~milenka http://www.ece.uah.edu/~lacasa. Overview. Types of Variables

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CPE 619 The Art of Data Presentation

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  1. CPE 619The Art of Data Presentation Aleksandar Milenković The LaCASA Laboratory Electrical and Computer Engineering Department The University of Alabama in Huntsville http://www.ece.uah.edu/~milenka http://www.ece.uah.edu/~lacasa

  2. Overview • Types of Variables • Guidelines for Preparing Good Charts • Common Mistakes in Preparing Charts • Pictorial Games • Special Charts for Computer Performance • Gantt Charts • Kiviat Graphs • Schumacher Charts • Decision Maker’s Games

  3. Types of Variables • Type of computer: Super computer, minicomputer, microcomputer • Type of Workload: Scientific, engineering, educational • Number of processors • Response time of system

  4. Guidelines for Preparing Good Charts • 1) Require minimum effort from the reader • Direct labeling vs. legend box • 2) Maximize Information • Words in place of symbols; cleary label the axes

  5. Guidelines (cont’d) • 3) Minimize ink • No grid lines, more details • 4) Use commonly accepted practices • origin at (0,0); independent variable (cause) along x axis; the dependent variable (effect) along the y axis; linear scales; increasing scales; equal divisions • 5) Avoid ambiguity • Show coordinate axes, scale divisions, origin;Identify individual curves and bars

  6. Checklist for Good Graphics • Are both coordinate axes shown and labeled? • Are the axes labels self-explanatory and concise? • Are the scales and divisions shown on both axes? • Are the minimum and maximum of the ranges shown on the axes appropriate to present maximum information • Is the number of curves reasonably small? • Do all graphs use the same scale? • Is there no curve that can be removed without reducing information? • Are the curves on a line chart individually labeled? • Are the cells in a bar chart individually labeled? • Are all symbols on the graph accompanied by appropriate textural explanations? • If the curves cross, are the line patterns different to avoid confusion? • Are the units of measurement indicated? • Is the horizontal scale increasing from left to right? • Is the vertical scale increasing from bottom to top? • Are the grid lines aiding in reading the curves? • Does this whole chart add to information available to the reader? • Are the scales contiguous? • Is the order of bars in a bar chart systematic? • If the vertical axis represents a random quantity, are confidence intervals shown? • Are there no curves, symbols, or texts on the graph that can be removed without affecting the information? • Is there a title for the whole chart? • Is the chart title self-explanatory and concise? • For bar charts with unequal class interval, is the are and width representative of the frequency and interval? • Do the variable plotted on this cart give more information that other alternatives? • Does the chart clearly bring out the intended message? • Is the figure referenced and discussed in the text of the report?

  7. Common Mistakes in Preparing Charts • Presenting too many alternatives on a single chart • Max 5 to 7 messages => Max 6 curves in a line charts, no more than 10 bars in a bar chart, max 8 components in a pie chart • Presenting many y variables on a single chart

  8. Common Mistakes in Charts (cont’d) • Using symbols in place of text • Placing extraneous information on the chart • E.g., grid lines, granularity of the grid lines • Selecting scale ranges improperly • Automatic selection by programs may not be appropriate

  9. 8000 8100 8300 8200 Common Mistakes in Charts (cont’d) • Using a line chart in place of column chart • line => continuity MIPS CPU Type

  10. Pictorial Games • Using non-zero origins to emphasize the difference • Three quarter high-rule => height/width > 3/4 Mine and yours are almost the same (conceal difference) Mine is much better than yours (emphasize difference) Height of the highest point should be at least ¾ of the horizontal offset of the rightmost point

  11. Pictorial Games (cont’d) • Using double-whammy graph for dramatization • Using related metrics

  12. Pictorial Games (cont’d) • Plotting random quantities without showing confidence intervals Means of two random variables Means are not enough. Overlapping confidence intervals usually means that the two random quantities are statistically indifferent.

  13. Pictorial Games (cont’d) • Pictograms scaled by height • Wrong scaling: Area(MINE) > 4*Area(YOURS)?? MinePerformance = 2 YoursPerformance = 1

  14. 2 0 8 6 4 2 0 8 6 4 Pictorial Games (cont’d) • Using inappropriate cell size in histograms Normal distribution Exponential distribution 12 12 10 10 Frequency Frequency [0,2) [2,4) [4,6) [6,8) [8,10) [10,12) [0,6) [6,12) Response Time Response Time

  15. 0 0 2 4 6 8 Pictorial Games (cont’d) • Using broken scales in column charts • Amplify differences 12 12 10 11 Resp. Time Resp. Time 10 9 F F A B C D E A B C D E System System

  16. Special Charts for Computer Performance • Gantt charts • Kiviat Graphs • Schumacher's charts

  17. Gantt Charts • Shows relative duration of a number of conditions 60 CPU 20 20 IO Channel 10 30 5 15 Network 0% 20% 40% 60% 80% 100% Utilization

  18. Example: Data for Gantt Chart

  19. Draft of the Gantt Chart

  20. Final Gantt Chart

  21. CPUBusy CPU inSupervisor State CPU OnlyBusy CPU/ChannelOverlap CPU inProblem State Channel onlyBusy CPUWait Any ChannelBusy Kiviat Graphs • Radial chart with even number of metrics • HB and LB metrics alternate • Ideal shape: star

  22. CPUBusy CPU inSupervisor State CPU OnlyBusy CPU inProblem State CPU/ChannelOverlap CPUWait Channel onlyBusy Any ChannelBusy Kiviat Graph for a Balanced System • Problem: Inter-related metrics • CPU busy = problem state + Supervisor state • CPU wait = 100 – CPU busy • Channel only – any channel –CPU/channel overlap • CPU only = CPU busy – CPU/channel overlap

  23. Shapes of Kiviat Graphs CPU Keel boat I/O Wedge I/O Arrow CPU bound system I/O bound system CPU- and I/O bound system

  24. Merrill’s Figure of Merit (FoM) • Performance = {x1, x2, x3, …, x2n}Odd values are HB and even values are LB • x2n+1 is the same as x1 • Average FOM = 50%

  25. Example: FoM • System A:

  26. FoM Example (Cont) • System B:System B has a higher figure of merit and it is better.

  27. Figure of Merit: Known Problems • All axes are considered equal • Extreme values are assumed to be better • Utility is not a linear function of FoM • Two systems with the same FoM are not equally good • System with slightly lower FoM may be better

  28. Kiviat Graphs For Other Systems • Use Kiviat graphs for networks ApplicationThroughput LinkOverhead Packets With Error Implicit Acknowledgements LinkUtilization Duplicate Packets

  29. Schumacher Charts • Performance matrix are plotted in a tabular manner • Values are normalized with respect to long term means and standard deviations • Any observations that are beyond mean  one standard deviation need to be explained • See Figure 10.25 in the book

  30. Performance Analysis Rat Holes Workload Metrics Configuration Details

  31. Reasons for not Accepting an Analysis • This needs more analysis. • You need a better understanding of the workload. • It improves performance only for long IOs/packets/jobs/files, and most of the IOs/packets/jobs/files are short. • It improves performance only for short IOs/packets/jobs/files, but who cares for the performance of short IOs/packets/jobs/files, its the long ones that impact the system. • It needs too much memory/CPU/bandwidth and memory/CPU/bandwidth isn't free. • It only saves us memory/CPU/bandwidth and memory/CPU/bandwidth is cheap. See Box 10.2 on page 162 of the book for a complete list

  32. Examples

  33. Summary • Qualitative/quantitative, ordered/unordered, discrete/continuous variables • Good charts should require minimum effort from the reader and provide maximum information with minimum ink • Use no more than 5-6 curves, select ranges properly, Three-quarter high rule • Gantt Charts show utilizations of various components • Kiviat Graphs show HB and LB metrics alternatively on a circular graph • Schumacher Charts show mean and standard deviations • Workload, metrics, configuration, and details can always be challenged. Should be carefully selected.

  34. Exercise 10.1 What type of chart (line or bar) would you use to plot: • CPU usage for 12 months of the year • CPU usage as a function of time in months • Number of I/O's to three disk drives: A, B, and C • Number of I/O's as a function of number of disk drives in a system

  35. Exercise 10.2 • List the problems with the following charts

  36. Exercise 10.3 • On a system consisting of 3 resources, called A, B, and C. The measured utilizations are shown in the following table. A zero in a column indicates that the resource is not utilized. Draw a Gantt chart showing utilization profiles.

  37. Exercise 10.4 • The measured values of the eight performance metrics listed in Example 10.2 for a system are: 70%, 10%, 60%, 20%, 80%, 30%, 50%, and 20%. Draw the Kiviat graph and compute its figure of merit.

  38. Exercise 10.5 • For a computer system of your choice, list a number of HB and LB metrics and draw a typical Kiviat graph using data values of your choice.

  39. Ratio Games

  40. Overview • Ratio Game Examples • Using an Appropriate Ratio Metric • Using Relative Performance Enhancement • Ratio Games with Percentages • Ratio Games Guidelines • Numerical Conditions for Ratio Games

  41. Case Study 11.1: 6502 vs. 8080 • Conclusion: 6502 is worse. It takes 4.7% more time than 8080. 1. Ratio of Totals

  42. 6502 vs. 8080 (Cont) 3. 8080 as the base: 2. 6502 as the base: • Ratio of Totals: 6502 is worse. It takes 4.7% more time than 8080. • With 6502 as a base: 6502 is better. It takes 1% less time than 8080. • With 8080 as a base: 6502 is worse. It takes 6% more time.

  43. Case Study 11.2: RISC vs. CISC • Conclusion: RISC-I has the largest code size. The second processor Z8002 requires 9% less code than RISC-I.

  44. RISC vs. CISC (Cont) • Conclusion: Z8002 has the largest code size and that it takes 18% more code than RISC-I. [Peterson and Sequin 1982] 8.00 11.00 13.00 10.50 8.50

  45. Using an Appropriate Ratio Metric Example: • Throughput: A is better • Response Time: A is worse • Power: A is better

  46. Using Relative Performance Enhancement • Example: Two floating point accelerators • Problem: Incomparable bases. Need to try both on the same machine

  47. Ratio Games with Percentages • Example: Tests on two systems 1. System B is better on both systems 2. System A is better overall. System A: System B:

  48. Percentages (Cont) • Other Misuses of Percentages: • 1000% sounds more impressive than 11-time. Particularly if the performance before and after the improvement are both small • Small sample sizes disguised in percentages • Base = Initial. 400% reduction in prices  Base = Final

  49. Ratio Games Guidelines • If one system is better on all benchmarks, contradicting conclusions can not be drawn by any ratio game technique

  50. Guidelines (cont) • Even if one system is better than the other on all benchmarks, a better relative performance can be shown by selecting appropriate base. • In the previous example, System A is 40% better than System B using raw data, 43% better using system A as a base, and 42% better using System B as a base. • If a system is better on some benchmarks and worse on others, contracting conclusions can be drawn in some cases. Not in all cases. • If the performance metric is an LB metric, it is better to use your system as the base • If the performance metric is an HB metric, it is better to use your opponent as the base • Those benchmarks that perform better on your system should be elongated and those that perform worse should be shortened

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