MPI: Message Passing Interface for Parallel Computing, Study notes of Computer Science

Download MPI: Message Passing Interface for Parallel Computing and more Study notes Computer Science in PDF only on Docsity! MPI MPI = message passing interface • No shared memory • More language-neutral than OpenMP Library (no new compiler) ⇒ essentially a grown-up bmsg.c Biased toward C and Fortran, but also implemented in other languages • Run-time manager helps launch processes Latest version is 2.0, but 1.3 is enough for our purposes 1 MPI Program Model Write one program... • Run-time manager runs it P times • Each process discovers its rank ⇒ role • Processes coordinate through explicit messages 2 MPI Architecture x.c x x x 5 MPI Architecture MPI run-time x.c x x x 6 MPI “Hello World” in C #include <stdio.h> #include <mpi.h> int main(int argc, char *argv[]) { int numprocs, rank, namelen; char processor_name[MPI_MAX_PROCESSOR_NAME]; MPI_Init(&argc, &argv); MPI_Comm_size(MPI_COMM_WORLD, &numprocs); MPI_Comm_rank(MPI_COMM_WORLD, &rank); MPI_Get_processor_name(processor_name, &namelen); printf("Process %d on %s out of %d\n", rank, processor_name, numprocs); MPI_Finalize(); } 7 MPI Basic Messages int me = MPI.COMM_WORLD.Rank(); int size = 1; int array[] = new int[size]; if (me == 0) { array[0] = 42; MPI.COMM_WORLD.Send(array, 0, size, MPI.INT, 1, 8); System.out.println("sent " + array[0]); } else { MPI.COMM_WORLD.Recv(array, 0, size, MPI.INT, 0, 8); System.out.println("got " + array[0]); } 10 Sending a Message To send: • Specificy data as array, size, and type • Specify target process (by its rank) • Specify a tag A kind of mailbox id within the target process Meaning of a tag is completely up to programmer 11 Receiving a Message To receive: • Specificy data area as array, size, and type • Specify source process (by its rank) or use ANY_SOURCE • Specify a tag or use ANY_TAG 12