Performance Analysis Lecture 2

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Questions and Answers

What is the impact of out-of-order packets on network performance?

They increase retransmission rates.

They consume buffers. (correct)

They improve response times.

They reduce the overall throughput.

What is likely to happen if too many packets are lost during transmission?

Retransmissions will decrease.

Disconnection may occur. (correct)

There will be no impact on performance.

The throughput will increase.

Which model is used when dealing with a system that is too difficult to measure directly?

Predictive models.

Empirical models.

Event-driven models.

Simulation models. (correct)

What should be considered a probability when analyzing network performance?

Probability of out-of-order arrivals. Signup and view all the answers

What does throughput refer to in the context of network performance?

The number of packets delivered per unit of time. Signup and view all the answers

What characterizes a time-invariant system?

Outputs depend on current and past inputs. Signup and view all the answers

Which statement about open systems is true?

They can experience changes from the outside world. Signup and view all the answers

What defines stochastic systems?

At least one input or internal state is random. Signup and view all the answers

Continuous time systems (CTS) differ from discrete time systems (DTS) in that:

CTS can experience changes at any possible time. Signup and view all the answers

What distinguishes continuous state systems from discrete state systems?

Continuous state systems possess an uncountable state space. Signup and view all the answers

How is Quality of Service (QoS) defined?

It is dependent on user satisfaction and application needs. Signup and view all the answers

Which of the following describes discrete time systems (DTS)?

They undergo state changes at prescribed intervals. Signup and view all the answers

Which classification applies primarily to computer and communication systems?

Dynamic and stochastic discrete-state systems. Signup and view all the answers

Which of the following best describes system-oriented measures?

Independent of specific applications. Signup and view all the answers

What is the main distinction between nominal capacity and usable capacity?

Usable capacity is achieved without exceeding a pre-specified response-time limit. Signup and view all the answers

Which performance metric reflects the ratio of usable capacity to nominal capacity?

Efficiency. Signup and view all the answers

What performance metric is typically used to measure the rate of requests handled in a system?

Throughput. Signup and view all the answers

Which of the following scenarios best illustrates application-oriented measures?

Evaluating frame rate in video conferencing. Signup and view all the answers

Which metric measures the average fraction of time a resource is being utilized?

Utilization. Signup and view all the answers

What does the mean time between errors quantify in reliability metrics?

The total time in an error-free operation. Signup and view all the answers

Which of the following would not typically be considered a system-oriented performance metric?

SNR (Signal-to-Noise Ratio). Signup and view all the answers

What is the main purpose of performance evaluation in computer systems?

To apply techniques to assess performance measures of systems Signup and view all the answers

Which of the following is NOT a typical objective of performance analysis?

Comparing hardware models Signup and view all the answers

What metrics are necessary to evaluate the performance of a system?

Jitter, processing times, and workload specifics Signup and view all the answers

What is meant by 'workload characterization' in the context of performance analysis?

Determining the requests made by users to the system Signup and view all the answers

Which of the following best describes 'capacity planning' in performance analysis?

It is concerned with how much resources to allocate for desired service quality Signup and view all the answers

What aspect of a system does determining the performance bottleneck address?

The part of the system that limits overall performance Signup and view all the answers

Which statement best describes the role of 'metrics' in performance analysis?

Metrics provide objective criteria for evaluating system performance. Signup and view all the answers

What scenario might suggest a performance study should be conducted?

Existing systems show slow response times during peak use Signup and view all the answers

What is a primary advantage of using simulation modeling?

It allows for a greater level of detail than analytical modeling. Signup and view all the answers

Which of the following is a disadvantage of simulation modeling?

It typically requires long simulation times. Signup and view all the answers

What is a key consideration when designing a simulation model?

The workload must represent how the system will function under various conditions. Signup and view all the answers

How can the accuracy of simulation results be described?

It is often measured in terms of confidence intervals. Signup and view all the answers

What common mistake can occur when setting goals for simulation modeling?

Ignoring the importance of having specific and realistic goals. Signup and view all the answers

What is generally NOT true about the setup of a simulation model?

The system should be overly simplified. Signup and view all the answers

What is a significant reason for longer simulation runtimes?

Achieving higher variability in outputs for better accuracy. Signup and view all the answers

Which evaluation technique should be most appropriate when conducting a performance analysis?

The technique should be based on the specific goals and context. Signup and view all the answers

What is a key requirement for presenting results effectively in analytic modeling?

Graphs should assist in making decisions. Signup and view all the answers

Which of the following is NOT a performance metric mentioned for evaluating service?

Total number of calls Signup and view all the answers

Which analytic method is suggested for values outside the scope of conducted experiments?

Analytic modeling Signup and view all the answers

What does the systematic approach to evaluating services entail?

Defining goals and selecting performance metrics. Signup and view all the answers

In the context of the case study, what is a primary distinction between remote pipes and remote procedure calls?

Remote procedure calls block the client until the server returns results. Signup and view all the answers

Which factor may significantly impact the performance of an application using either rpipe or rpc?

The distance between the client and server. Signup and view all the answers

Why is it essential to list assumptions and limitations in the study?

They provide context for applying results accurately. Signup and view all the answers

In the experimental design phase, what is indicated by a full factorial approach?

Evaluating all possible combinations of factors. Signup and view all the answers

What kind of data is primarily focused on when monitoring resources during workload evaluation?

The amount of data being transferred in requests Signup and view all the answers

Which of the following parameters is NOT considered when analyzing system performance?

Client's previous workload history Signup and view all the answers

Study Notes

Performance Analysis of Computer Systems and Networks - Lecture 2

Raj Jain's book, "The Art of Computer Systems Performance Analysis," is the primary text. Published in 1991, it covers experimental design, measurement, simulation, and modeling.
Most lecture slides are directly from the author, Professor Raj Jain.

Performance Evaluation

Performance evaluation applies techniques (measurements, analytical/simulation modeling) to existing or envisioned systems.
It's used to assess performance measures like delay, response times, throughput, jitter, and processing times.
Performance is a crucial non-functional aspect of hardware and software systems.

Basic Terms

System: A collection of hardware, software, and firmware.
Metrics (Measures): Criteria used to assess system performance.
Workloads: User requests made to the system.

CMPE-474 Objectives

Specify performance requirements for systems.
Evaluate design alternatives and compare systems.
Determine optimal parameter values (system tuning).
Identify performance bottlenecks.
Characterize system workload.
Plan capacity for components (number and sizes).
Forecast performance under future loads.

Typical Reasons for a Performance Study

Identify and resolve performance bottlenecks in existing systems.
Plan future system capacity to provide the desired service level.
Compare different systems, algorithms, or protocols.
Validate performance guarantees made by providers.

Performance Modeling

Modeling simplifies systems by capturing only their essential performance aspects.
It's easier to understand modeling principles (e.g., probability theory, simulation methodology) than the whole modeling process.
A thorough understanding of the system being modeled is crucial for effective modeling.

Examples

Example I: Performance metrics to compare disk drives, transaction-processing systems, and packet-retransmission algorithms.
Example II: Suitable monitors (software or hardware) to measure processor instruction counts, multiprogramming degree, and network packet response times.
Example III: Evaluating network links based on packet loss data for different file sizes.
Example IV: Database system response time analysis using a queueing model.
Example 1: Comparing system throughput between A and B under different workloads.
Example 2: Comparing computer system performance for executing different programs.
Example 2 cont: Calculating total execution time under real workload conditions.
Example 3: Discusses network components (hardware, software, and communication channels) and introduces their error model.
Example 4: Discusses classifying systems as either static or dynamic, time-varying or invariant as well as open or closed.

QoS (Quality of Service)

System performance is often described by "quality of service" or QoS.
QoS is application dependent; specific requirements depend on the application (frame rate, sound quality, bandwidth or latency).

Common Performance Measures

Response Time/Reaction Time: Time from when a request is submitted to when the response is received.
Throughput: The rate of requests completed per unit of time (e.g. jobs per second, packets per second).
Efficiency: The ratio of used capacity to total capacity.
Utilization: The fraction of time a resource is busy.
Reliability: The probability or mean time between errors.
Availability: The probability of a system being available when needed. Commonly calculated via Mean Time To Failure and Mean Time To Repair.
Delay (Communication): Measured end-to-end or round-trip; also includes delays in network elements.
Jitter: Variability in delay.
Loss Rate: Fraction of packets lost or erroneous.
Utilization (Communication): Fraction of time a resource or link is busy.
Blocking Probability: Probability of failing to get service or failing to connect.
Dropping Probability: Probability of an ongoing session losing connection.

Measurement, Simulation, and Analytical modeling

Describe techniques.
When measurement is the correct technique to describe (or model) existing systems
When Analytic modeling or Simulation modeling (using mathematical concepts, or computer models) is the correct technique to describe/model systems or parts of complex systems.
Discuss the advantages and disadvantages of each methodology.
Methods to evaluate results.
Identify potential sources of error.

Case Studies

Congestion Control Algorithms: Performance metrics for packet delivery (in-order, out-of-order, duplicates, loss).

Common Mistakes

Problems to watch out for when studying performance (e.g., poorly defined goals, inappropriate methodology or workload).

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Description

Explore the key concepts from Raj Jain's 'The Art of Computer Systems Performance Analysis' in this lecture. This session covers performance evaluation techniques like measurements and modeling, with a focus on metrics for assessing system performance. Join to deepen your understanding of critical performance aspects in computer systems and networks.