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

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

  • MPI_Send
  • MPI_Init (correct)
  • MPI_Comm_size
  • MPI_Comm_rank

    • What is the purpose of the MPI_Comm_size function?

  • Receive a message from another process
  • Get the size of a communicator (correct)
  • Send a message to another process
  • Get the rank of the calling process in the communicator

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

  • Non-blocking communication functions
  • Asynchronous communication functions
  • Synchronous communication functions
  • Blocking communication functions (correct)

    • What is the purpose of the MPI_Finalize function?

    <p>Clean up all MPI state</p> Signup and view all the answers

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

    <p>Blocking functions require event completion, while non-blocking functions do not</p> Signup and view all the answers

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

    <p>6</p> Signup and view all the answers

    What does the MPI_Status object provide information about?

    <p>The source process for the message, the message tag, and error status</p> Signup and view all the answers

    What is the purpose of the MPI_Get_count function?

    <p>To get the number of elements received in the message</p> Signup and view all the answers

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

    <p>To increase the performance by overlapping computation with communication</p> Signup and view all the answers

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

    <p>To ensure the buffer is free for reuse</p> Signup and view all the answers

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

    <p>To first get your program working using blocking communication</p> Signup and view all the answers

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

    <p>Blocking functions wait for the communication to complete, while non-blocking functions return without waiting</p> Signup and view all the answers

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

    <p>To enable simultaneous data transfer and computation</p> Signup and view all the answers

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

    <p>MPI_Bcast</p> Signup and view all the answers

    What is the difference between MPI_Scatter and MPI_Gather?

    <p>MPI_Scatter sends data from one process to all, while MPI_Gather collects data from all to one</p> Signup and view all the answers

    What is the main use of broadcasting in MPI?

    <p>To send out user input to a parallel program</p> Signup and view all the answers

    What is the difference between MPI_Alltoall and MPI_Alltoallv?

    <p>MPI_Alltoall sends a fixed amount of data to each process, while MPI_Alltoallv sends a customizable amount of data to each process</p> Signup and view all the answers

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

    <p>MPI_Send</p> Signup and view all the answers

    What is the purpose of the MPI_Bcast function?

    <p>To send data from the root process to all other processes</p> Signup and view all the answers

    What happens when a receiver process calls MPI_Bcast?

    <p>The data variable is filled in with the data from the root process</p> Signup and view all the answers

    What is the purpose of the MPI_Barrier function?

    <p>To synchronize all processes in a group</p> Signup and view all the answers

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

    <p>MPI_Reduce</p> Signup and view all the answers

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

    <p>the operation to be performed (e.g. MPI_MAX, MPI_MIN)</p> Signup and view all the answers

    What happens when a process reaches an MPI_Barrier call?

    <p>The process blocks until all tasks in the group reach the same MPI_Barrier call</p> Signup and view all the answers

    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.

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    Description

    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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