Computer Science 335
Parallel Processing and High Performance Computing

Fall 2026, Siena University

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Agenda

• Announcements
  • Create your ACCESS accounts and email me your ids so we can get set up for supercomputer access
  • Lab 5: Non-Blocking Messages [HTML] [PDF], Lab 6: Collective Communication Practice [HTML] [PDF], and Programming Project 3: MPI Recursive Digit Sum [HTML] [PDF] should be wrapped up
  • Programming Project 4: Collective Communication [HTML] [PDF] should be wrapping up
  • Programming Project 5: Parallelizing Jacobi Iteration [HTML] [PDF] time to get started
• Finishing up our discussion of Question 3.11 from Pacheco
  • first: thinking about some fundamental communication patterns
    • broadcast
    • reduce
    • allreduce
  • the trickier one: scan (relevant to 3.11)
• Example: MPI implementation of Conway's Game of Life
  • Uses a distributed data structure: Each process maintains its own subset of the computational domain, in this case just some of the rows of the grid. Other processes do not know about the data on a given process. Only the data that is needed to compute the next generation, a one-cell overlap (sometimes called ghost cells or a halo), is exchanged between neighbors before each iteration.
  • When we need to get a global count of some statistic, such as the count of live cells at the start, we use a reduction.
  • The communication of cell data between iterations is done with two pairs of sends and receives. Here, we use nonblocking calls, then wait for their completion with the MPI_Waitall call.
  • This example also shows a technique for writing a file when the intended contents are distributed among a set of processes.

Terminology

• ghost cells/halo

Examples

• mpilife: MPI parallelization of the Conway's Game of Life simulator