Assessing & Understanding Performance Flashcards
What is the key factor that determines the effectiveness of a computer system?
Hardware performance
Hardware performance is crucial for the effectiveness of both hardware and software.
What are the major performance parameters in computer systems?
Response time (execution time)
Throughput (bandwidth)
Response time refers to the time taken to complete a task, while throughput refers to the amount of work done in a given time.
What is response time also known as?
Execution time
Response time indicates how long it takes for a job to run.
What does throughput measure?
Total amount of work done in a given time
Throughput is also referred to as bandwidth.
How is machine clock rate expressed?
In MHz or GHz
The clock rate is the inverse of clock cycle time.
What is the relationship between clock cycles and execution time?
Execution time = # CPU clock cycles x clock cycle time
Execution time can also be calculated using clock rate.
What is CPU execution time?
Time the CPU spends working on a task
It does not include time spent waiting for I/O or running other programs.
What counts in elapsed time?
Disk and memory accesses, I/O, etc.
Elapsed time includes all operations, making it useful but not ideal for comparisons.
How do you improve performance?
Decrease the # of required cycles for a program
Decrease the clock cycle time
Increase the clock rate
These adjustments can lead to improved performance.
What is CPI?
Clock cycles per instruction
CPI represents the average number of clock cycles each instruction takes to execute.
What is the formula for overall effective CPI?
Effective CPI = Σ (CPIi x ICi)
Where ICi is the instruction count for instruction class i.
What does Amdahl’s Law state?
Performance enhancement is limited by the amount that the improved feature is used
It helps to understand the impact of improvements on program execution time.
What is the arithmetic mean used for in performance measurement?
To summarize performance for a benchmark set with a single number
A smaller mean indicates better performance.
How do you calculate CPU execution time?
CPU execution time = # CPU clock cycles for a program x clock cycle time
This calculation helps determine the total time a program takes to execute.
What is the formula for calculating performance?
CPU time = Instruction count x CPI x clock cycle time
This equation helps assess the performance of a program on a specific machine.
What does Amdahl’s Law describe?
The theoretical speedup of a task when only part of it is improved
Amdahl’s Law helps to understand the limitations of performance improvement based on the proportion of the task that can be enhanced.
In Amdahl’s Law, what does the variable ‘n’ represent?
Amount of Improvement
‘n’ is used to quantify how much faster a specific part of a task needs to be in order to achieve the desired overall speedup.
If trying to increase the entire execution time by a factor of 5, what is the outcome?
Cannot be done
The calculations show that with the given parameters, it is impossible to achieve the desired speedup.
List three benchmarks from the SPEC CPU2000.
- perl
- bzip2
- gcc
These benchmarks are used to measure the performance of processors.
What is the most important metric for power-limited applications?
Energy efficiency
Energy efficiency is crucial, especially in embedded systems where battery life is a major concern.
What are static metrics in evaluating ISAs?
- Memory occupancy
- Instruction count
Static metrics provide a snapshot of resource usage without executing the program.
What is the best metric for evaluating the performance of a program?
Time to execute the program
Execution time offers a direct measure of performance effectiveness.
What factors can lead to performance increases in a given architecture?
- Increases in clock rate
- Improvements in processor organization
- Compiler enhancements
- Algorithm/Language choices
These factors contribute to the overall efficiency and speed of a processor.
True or False: Performance is specific to a particular program.
True
Performance can vary significantly depending on the program being executed.
