Message Passing Interface

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Message Passing Interface

• ???

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MPI is

• An interface for parallel computing programming
• Not programming paradigm
• Language Independent
• Multi Process Multi Data

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MPI - non deterministic(default)

• The arrival order of messages is not defined
• responsibility of programmer
• to ensure the order of messages

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MPI - global operation

• Suite of specialized collective communication
  functions
• barrier synchronizes all process
• broadcast sends data from one process to all
  processes
• gather gathers data from all process to one
  processes
• scatter scatters data from one process to all
  processes
• reduction operations sums, multiplies, etc.,
  distributed data

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MPI - barrier

• Synchronize execution of a group of processes
• ? MPI_BARRIER
• Barrier is a simple way of separating two phases

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MPI - data movement

• Collective data movement routines
• ? MPI_BCAST, MPI_GATHERM, MPI_SCATTER

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MPI - reduction operation

• Reduction operation
• ? MPI_REDUCE, MPI_ALLREDUCE

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MPI - asynchronous communication

• When a computation must access elecments of a
  shared data structure in an unstructed manner,
• There must be asynchronous communication

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MPI - modularity
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MPI - other features

• derived datatypes
• allowing noncontiguous data elements to be
  grouped together in a message
• Construct function ? MPI_TYPE_CONTIGUOUS,
  MPI_TYPE_VECTOR, MPI_TYPE_INDEXED
• Commit function ? MPI_TYPE_COMMIT
• Free function ? MPI_TYPE_FREE
• Heterogeneous type
• - different datatypes can be encapsulated in a
  single derived type

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MPI - other features

• Environmental inquiry
• - a program can obtain information about the
  environment in which it is running, information
  that can be used to tune algorithm performance
• Additional global operations
• - Operations supporting all-to-all communication,
  variable-sized contributions, reduction
  operations, etc.

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MPI - other features

• Specialized communication modes
• Blocking sender to synchronous communication with
  receiver
• Buffered communications