Parallel Programming Models

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Questions and Answers

What is a necessary requirement for efficient implementation of a NUMA system?

  • Specialized software library
  • Hardware support (correct)
  • Message passing model
  • Shared address space

What is a characteristic of the message passing model of communication?

  • Threads operate within a shared address space
  • Threads communicate by sending and receiving messages (correct)
  • Threads operate on a first-come-first-served basis
  • Threads can access any address in the system

What is the primary advantage of using the message passing model?

  • It allows for more efficient use of memory
  • It enables the connection of commodity systems to form a large parallel machine (correct)
  • It is a more straightforward way to implement parallelism
  • It is more scalable than other parallel models

How do threads communicate in the message passing model?

<p>By sending and receiving messages (A)</p>
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What is a popular software library for implementing the message passing model?

<p>MPI (D)</p>
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What is a key difference between the shared address space model and the message passing model?

<p>The message passing model uses a shared address space, while the shared address space model uses message passing (A)</p>
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What is a potential disadvantage of using the NUMA architecture?

<p>It is expensive (B)</p>
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What is a key advantage of the message passing model?

<p>It allows for the connection of commodity systems to form a large parallel machine (B)</p>
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What is a characteristic of the NUMA architecture?

<p>Any processor can access any address in the system (B)</p>
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What is a key challenge in implementing the message passing model?

<p>Reasoning about locality for performance (A)</p>
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What is the characteristic of the data-parallel model?

<p>Very rigid computation structure (C)</p>
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What is the foreach construct equivalent to in the data-parallel model?

<p>A map function (A)</p>
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What is the main characteristic of the shared address space model?

<p>All threads can read and write to all shared variables (B)</p>
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What is the significance of the Connection Machine (CM-1, CM-2) in the history of parallel computing?

<p>It had thousands of processors, one instruction decode unit (C)</p>
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What is the benefit of using the data-parallel model in MATLAB?

<p>It allows for the same operation on each element of an array (A)</p>
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What is the significance of the Cray supercomputers in the history of parallel computing?

<p>They had vector processors (B)</p>
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What is the main advantage of using SPMD programming in the data-parallel model?

<p>It allows for implicit synchronization at the end of the map (C)</p>
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What is the main difference between the data-parallel model and the message-passing model?

<p>Message-passing model has highly structured communication (D)</p>
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What is the primary mechanism of communication in the shared address space model?

<p>Reading and writing to shared variables (C)</p>
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What is the purpose of synchronization primitives in the shared address space model?

<p>To ensure thread safety (D)</p>
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How do threads communicate in the shared address space model?

<p>Implicitly through memory operations (D)</p>
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What is an example of a shared variable in the shared address space model?

<p>A shared array (C)</p>
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Why is the shared address space model a natural extension of sequential programming?

<p>Because it assumes a shared address space (D)</p>
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What is the role of locks in the shared address space model?

<p>To ensure thread safety (C)</p>
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How do threads access shared variables in the shared address space model?

<p>By reading and writing directly (C)</p>
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What is a characteristic of the shared address space model?

<p>Implicit communication through memory operations (A)</p>
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What is the purpose of the shared address space model?

<p>To provide a natural extension of sequential programming (A)</p>
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What is a benefit of using the shared address space model?

<p>Simplified communication between threads (A)</p>
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Study Notes

Parallel Programming Models

  • There are three models of communication: Shared Address Space, Message Passing, and Data-Parallel.

Shared Address Space Model

  • Threads communicate by reading and writing to shared variables.
  • Shared variables are like a big bulletin board, where any thread can read or write to shared variables.
  • Synchronization primitives are also shared variables, such as locks.
  • Threads communicate implicitly through memory operations.
  • This model is a natural extension of sequential programming, but requires hardware support to implement efficiently.

Message Passing Model

  • Threads operate within their own private address spaces.
  • Threads communicate by sending and receiving messages.
  • A message includes a recipient, a buffer to be transmitted, and an optional message identifier (or "tag").
  • Sending messages is the only way to exchange data between threads.
  • Message passing is a programming model for clusters, where commodity systems can be connected to form a large parallel machine.

Data-Parallel Model

  • The model imposes a very rigid computation structure, where programs perform the same function on different data elements in a collection.
  • Historically, it was used for SIMD (Single Instruction, Multiple Data) supercomputers and vector processors.
  • Today, it often takes the form of SPMD (Single Program, Multiple Data) programming, where a function is applied to each element of a collection independently.
  • Synchronization is implicit at the end of the map (or loop).
  • Examples include Matlab and ISPC (Intermediate-Scale Parallel Computing).

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