TAILIEUCHUNG - Parallel Programming: for Multicore and Cluster Systems- P23

Parallel Programming: for Multicore and Cluster Systems- P23: Innovations in hardware architecture, like hyper-threading or multicore processors, mean that parallel computing resources are available for inexpensive desktop computers. In only a few years, many standard software products will be based on concepts of parallel programming implemented on such hardware, and the range of applications will be much broader than that of scientific computing, up to now the main application area for parallel computing | 212 5 Message-Passing Programming started with MPI_Isend and respectively. After control returns from these operations senioffset and recvoffset are re-computed and MPI_Wait is used to wait for the completion of the send and receive operations. According to 135 the non-blocking version leads to a smaller execution time than the blocking version on an Intel Paragon and IBM SP2 machine. Communication Mode MPI provides different communication modes for both blocking and non-blocking communication operations. These communication modes determine the coordination between a send and its corresponding receive operation. The following three modes are available. Standard Mode The communication operations described until now use the standard mode of communication. In this mode the MPI runtime system decides whether outgoing messages are buffered in a local system buffer or not. The runtime system could for example decide to buffer small messages up to a predefined size but not large messages. For the programmer this means that he cannot rely on a buffering of messages. Hence programs should be written in such a way that they also work if no buffering is used. Synchronous Mode In the standard mode a send operation can be completed even if the corresponding receive operation has not yet been started if system buffers are used . In contrast in synchronous mode a send operation will be completed not before the corresponding receive operation has been started and the receiving process has started to receive the data sent. Thus the execution of a send and receive operation in synchronous mode leads to a form of synchronization between the sending and the receiving processes The return of a send operation in synchronous mode indicates that the receiver has started to store the message in its local receive buffer. A blocking send operation in synchronous mode is provided in MPI by the function MPI_Ssend which has the same parameters as MPI_Send with .

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