Distributed Systems and Cloud Computing: Message Passing Interface (MPI) Core Functions

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24 Questions

Which MPI function must be the first routine called to initialize the MPI library?

MPI_Init

What is the purpose of the MPI_Comm_size function?

Get the size of a communicator

What type of communication functions in MPI require certain events to be completed before the call is finished?

Blocking communication functions

What is the purpose of the MPI_Finalize function?

Clean up all MPI state

What is the main difference between blocking and non-blocking communication functions in MPI?

Blocking functions require event completion, while non-blocking functions do not

How many core MPI functions are necessary to write most MPI programs?

6

What does the MPI_Status object provide information about?

The source process for the message, the message tag, and error status

What is the purpose of the MPI_Get_count function?

To get the number of elements received in the message

What is the primary use of non-blocking communication functions?

To increase the performance by overlapping computation with communication

What is the responsibility of the programmer when using non-blocking communication functions?

To ensure the buffer is free for reuse

What is recommended before attempting to use non-blocking communication functions?

To first get your program working using blocking communication

What is the difference between blocking and non-blocking communication functions?

Blocking functions wait for the communication to complete, while non-blocking functions return without waiting

What is the purpose of non-blocking communication in MPI?

To enable simultaneous data transfer and computation

Which MPI function is used to send a message from one process to all other processes in a group?

MPI_Bcast

What is the difference between MPI_Scatter and MPI_Gather?

MPI_Scatter sends data from one process to all, while MPI_Gather collects data from all to one

What is the main use of broadcasting in MPI?

To send out user input to a parallel program

What is the difference between MPI_Alltoall and MPI_Alltoallv?

MPI_Alltoall sends a fixed amount of data to each process, while MPI_Alltoallv sends a customizable amount of data to each process

Which of the following functions is not a type of collective communication in MPI?

MPI_Send

What is the purpose of the MPI_Bcast function?

To send data from the root process to all other processes

What happens when a receiver process calls MPI_Bcast?

The data variable is filled in with the data from the root process

What is the purpose of the MPI_Barrier function?

To synchronize all processes in a group

What is the function to perform a reduction operation among processes?

MPI_Reduce

What is the parameter of the MPI_Reduce function that specifies the operation to be performed?

the operation to be performed (e.g. MPI_MAX, MPI_MIN)

What happens when a process reaches an MPI_Barrier call?

The process blocks until all tasks in the group reach the same MPI_Barrier call

Study Notes

MPI Core Functions

  • MPI_Init: initializes the MPI library, must be the first routine called
  • MPI_Comm_size: gets the size of a communicator
  • MPI_Comm_rank: gets the rank of the calling process in the communicator
  • MPI_Send: sends a message to another process
  • MPI_Recv: receives a message from another process
  • MPI_Finalize: cleans up all MPI state, must be the last MPI function called by a process

MPI Communication Functions

Blocking Communication

  • Completion of the call is dependent on certain events (e.g., data sent or safely copied to system buffer space)
  • Functions: MPI_Send, MPI_Recv
  • Status object provides information about: source process, message tag, error status
  • MPI_Get_count returns the number of elements received

Non-blocking Communication

  • Communication routine returns without waiting for completion
  • Programmer's responsibility to ensure buffer is free for reuse
  • Functions: MPI_Isend, MPI_Irecv
  • Used to increase performance by overlapping computation with communication

Data Movement (Collective Communication)

  • MPI_Bcast: broadcasts a message from the process with rank "root" to all other processes in the group
  • MPI_Scatter: splits the message into n equal segments and sends each segment to a different process
  • MPI_Gather: collects data from all processes in the group and sends it to a single process
  • MPI_Alltoall: performs an all-to-all communication where every process sends and receives n data segments
  • MPI_Alltoallv: a generalization of MPI_Alltoall where each process sends/receives a customizable amount of data

Broadcasting with MPI

  • MPI_Bcast: sends the same data to all processes in a communicator
  • Used for sending user input to a parallel program or configuration parameters to all processes
  • MPI_Bcast function: MPI_Bcast(void* data, int count, MPI_Datatype datatype, int sender, MPI_Comm communicator)

Synchronization (Collective Communication)

  • MPI_Barrier: causes each process to block until all tasks in the group reach the same MPI_Barrier call
  • Used for synchronization between processes

Reductions (Collective Computation)

  • MPI_Reduce: collects data from the other members and performs an operation (min, max, add, multiply, etc.) on that data
  • Examples of operations: MPI_MAX, MPI_MIN, MPI_SUM, MPI_PROD, etc.

Test your understanding of the core functions in Message Passing Interface (MPI) used in Distributed Systems and Cloud Computing. This quiz covers the essential MPI functions, including MPI_Init, MPI_Comm_size, and MPI_Comm_rank.

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