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### 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

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

Types of Variables

- Type of computer: Super computer, minicomputer, microcomputer
- Type of Workload: Scientific, engineering, educational
- Number of processors
- Response time of system

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

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

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?

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

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

8100

8300

8200

Common Mistakes in Charts (cont’d)- Using a line chart in place of column chart
- line => continuity

MIPS

CPU Type

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

Pictorial Games (cont’d)

- Using double-whammy graph for dramatization
- Using related metrics

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.

Pictorial Games (cont’d)

- Pictograms scaled by height
- Wrong scaling: Area(MINE) > 4*Area(YOURS)??

MinePerformance = 2

YoursPerformance = 1

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

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

Special Charts for Computer Performance

- Gantt charts
- Kiviat Graphs
- Schumacher's charts

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

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

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

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

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%

Example: FoM

- System A:

FoM Example (Cont)

- System B:System B has a higher figure of merit and it is better.

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

Kiviat Graphs For Other Systems

- Use Kiviat graphs for networks

ApplicationThroughput

LinkOverhead

Packets

With Error

Implicit Acknowledgements

LinkUtilization

Duplicate Packets

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

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

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.

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

Exercise 10.2

- List the problems with the following charts

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.

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.

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.

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

Case Study 11.1: 6502 vs. 8080

- Conclusion: 6502 is worse. It takes 4.7% more time than 8080.

1. Ratio of Totals

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.

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.

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

Using an Appropriate Ratio Metric

Example:

- Throughput: A is better
- Response Time: A is worse
- Power: A is better

Using Relative Performance Enhancement

- Example: Two floating point accelerators
- Problem: Incomparable bases. Need to try both on the same machine

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:

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

Ratio Games Guidelines

- If one system is better on all benchmarks, contradicting conclusions can not be drawn by any ratio game technique

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

Numerical Conditions for Ratio Games

- Raw Data

- A is better than B iff

- With A as the Base

- A is better than B iff

Numerical Conditions (Cont)

2

B is betterusing all 3

Ratio of B/A response on benchmark j

1

A isbetterusing all 3

Base B

Raw Data

Base A

0

1

1

1

2

3

Ratio of B/A response on benchmark i

Summary

- Ratio games arise from use of incomparable bases
- Ratios may be part of the metric
- Relative performance enhancements
- Percentages are ratios
- For HB metrics, it is better to use opponent as the base

Exercise 11.1

- The following table shows execution times of three benchmarks I, J, and K on three systems A, B, and C. Use ratio game techniques to show the superiority of various systems.

Exercise 11.2

- Derive conditions necessary for you to be able to use the technique of combined percentages to your advantage.

Homework

- Read chapter 10&11

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