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Questions and Answers
What is the primary factor that affects communication time in parallel programming?
What is the primary factor that affects communication time in parallel programming?
- Network structure and network contention (correct)
- Startup time only
- Network contention alone
- Transmission time to send one data word
What is the formula to calculate the communication time (tcomm) in parallel programming?
What is the formula to calculate the communication time (tcomm) in parallel programming?
- tcomm = tstartup + ntdata + tcomp
- tcomm = tstartup * ntdata
- tcomm = tstartup / ntdata
- tcomm = tstartup + ntdata (correct)
What is the unit of measurement for startup time and data transmission time in parallel programming?
What is the unit of measurement for startup time and data transmission time in parallel programming?
- Bytes
- Computational steps (correct)
- Seconds
- Milliseconds
What is the purpose of adding tcomp and tcomm together in parallel programming?
What is the purpose of adding tcomp and tcomm together in parallel programming?
Why is it sufficient to consider only one process when calculating the final communication time?
Why is it sufficient to consider only one process when calculating the final communication time?
What is the assumption made about routing when calculating communication time?
What is the assumption made about routing when calculating communication time?
What is the term for the time it takes to send a message with no data?
What is the term for the time it takes to send a message with no data?
What is the term for the time it takes to send one data word?
What is the term for the time it takes to send one data word?
What is the primary purpose of a space-time diagram in parallel programming?
What is the primary purpose of a space-time diagram in parallel programming?
Which of the following is a characteristic of visualization tools in parallel programming?
Which of the following is a characteristic of visualization tools in parallel programming?
What is the purpose of the MPI_Wtime() routine in parallel programming?
What is the purpose of the MPI_Wtime() routine in parallel programming?
How can the execution time between two points in the code be measured in parallel programming?
How can the execution time between two points in the code be measured in parallel programming?
What is the primary advantage of using hardware performance monitors in parallel programming?
What is the primary advantage of using hardware performance monitors in parallel programming?
Which of the following is a type of visualization tool available for MPI implementations?
Which of the following is a type of visualization tool available for MPI implementations?
What is the primary purpose of processor synchronization in parallel execution?
What is the primary purpose of processor synchronization in parallel execution?
What is a common challenge in parallel programming?
What is a common challenge in parallel programming?
What is a key drawback of using Amdahl's law and empirical observations in evaluating parallel programs?
What is a key drawback of using Amdahl's law and empirical observations in evaluating parallel programs?
What is the main reason why conventional modeling is not practical for parallel programmers?
What is the main reason why conventional modeling is not practical for parallel programmers?
What is the primary component of parallel execution time, tp, in addition to the number of computational steps, tcomp?
What is the primary component of parallel execution time, tp, in addition to the number of computational steps, tcomp?
What is the purpose of counting the number of computational steps in estimating the computational time, tcomp?
What is the purpose of counting the number of computational steps in estimating the computational time, tcomp?
What is a common assumption made in analyzing the computation time, tcomp?
What is a common assumption made in analyzing the computation time, tcomp?
What is the main benefit of using a performance modeling technique with intermediate-level detail?
What is the main benefit of using a performance modeling technique with intermediate-level detail?
What is the relationship between the sequential execution time, ts, and the number of computational steps?
What is the relationship between the sequential execution time, ts, and the number of computational steps?
What is the purpose of breaking down the computation time, tcomp, into parts?
What is the purpose of breaking down the computation time, tcomp, into parts?
What can be established using ts, tcomp, and tcomm?
What can be established using ts, tcomp, and tcomm?
What is the primary challenge in getting a parallel program to work properly?
What is the primary challenge in getting a parallel program to work properly?
What is the effect of instrumentation code on parallel programs?
What is the effect of instrumentation code on parallel programs?
What is a limitation of traditional debugging tools in parallel programming?
What is a limitation of traditional debugging tools in parallel programming?
What is the purpose of the computation/communication ratio?
What is the purpose of the computation/communication ratio?
What is the relationship between the number of processors, p, and the speedup factor?
What is the relationship between the number of processors, p, and the speedup factor?
What is the primary challenge in evaluating parallel programs empirically?
What is the primary challenge in evaluating parallel programs empirically?
What is the purpose of establishing the speedup factor and computation/communication ratio?
What is the purpose of establishing the speedup factor and computation/communication ratio?
What is the primary characteristic of asynchronous message passing routines?
What is the primary characteristic of asynchronous message passing routines?
What is the main difference between blocking and non-blocking operations in MPI?
What is the main difference between blocking and non-blocking operations in MPI?
What is the purpose of using asynchronous message passing routines in parallel programming?
What is the purpose of using asynchronous message passing routines in parallel programming?
What is the implication of using non-blocking operations in MPI?
What is the implication of using non-blocking operations in MPI?
What is the primary benefit of using asynchronous message passing routines in parallel programming?
What is the primary benefit of using asynchronous message passing routines in parallel programming?
What is the main consideration when using asynchronous message passing routines?
What is the main consideration when using asynchronous message passing routines?
What is the difference between asynchronous message passing routines and other message passing routines?
What is the difference between asynchronous message passing routines and other message passing routines?
What is the implication of using blocking operations in MPI?
What is the implication of using blocking operations in MPI?
Study Notes
Evaluating Parallel Programs
- A good performance model should explain available observations and predict future circumstances.
- Amdahl's law, empirical observations, and asymptotic analysis do not satisfy these requirements.
- Conventional modeling is not practical for parallel programmers due to detailed simulations of hardware components.
Performance Modeling
- Sequential execution time (ts) is estimated by counting the computational steps of the best sequential algorithm.
- Parallel execution time (tp) is the sum of computational time (tcomp) and communication overhead (tcomm): tp = tcomp + tcomm.
Computational Time
- Computational time (tcomp) is counted by the number of computational steps.
- When multiple processes are executed simultaneously, the computational steps of the most complex process are counted.
- tcomp is generally a function of n and p, i.e., tcomp = f(n, p).
- Computational time can be broken down into parts: tcomp = tcomp1 + tcomp2 + tcomp3 + …
Debugging and Evaluating Parallel Programs
- Visualization tools can be used to debug and evaluate parallel programs by watching them execute in a space-time diagram.
- Implementations of visualization tools are available for MPI, such as the Upshot program visualization system.
- Hardware performance monitors (which do not usually affect performance) are also available.
Evaluating Programs Empirically
- Measuring execution time can be done by using the MPI_Wtime() routine or by using the time() function to calculate the elapsed time between two points in the code.
Communication Time
- Communication time (tcomm) is the sum of startup time (tstartup) and transmission time (tdata): tcomm = tstartup + ntdata.
- tstartup is the time to send a message with no data, and tdata is the transmission time to send one data word.
Benchmark Factors
- The speedup factor and computation/communication ratio can be established using ts, tcomp, and tcomm.
- These ratios are functions of the number of processors (p) and the number of data elements (n).
Low-level Debugging
- Debugging parallel programs can be challenging due to the varying orders of execution possible.
- Instrumentation code can slow down a parallel program and cause nonworking programs to work.
Asynchronous Message Passing
- Asynchronous message passing routines do not wait for actions to complete before returning.
- They usually require local storage for messages and must be used with care.
MPI Definitions of Blocking and Non-Blocking
- Blocking routines return after local actions are complete, though the message transfer may not have been completed.
- Non-blocking routines return immediately, assuming that data storage used for transfer is not modified by subsequent statements prior to being used for transfer.
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Description
This quiz assesses understanding of evaluating parallel programs, including limitations of Amdahl's law, empirical observations, and asymptotic analysis in modeling parallelism. It covers the importance of a good performance model in explaining observations and predicting future circumstances.
