ih4cku / blog

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Open ih4cku opened 7 years ago

ih4cku commented 7 years ago

# openmpi 1.8.8
$ ./configure --with-cuda --with-threads=posix --enable-mpi-thread-multiple

ih4cku commented 7 years ago

introduction

MPI

interface standard defined in Supercomputing 1992 conference and finished implementation in 1995

communicator: defines a group of processes
- MPI_COMM_WORLD is the predefined communicator that includes all of the MPI processes
rank: process id within the group
tag: message indentifier

ih4cku commented 7 years ago

difference between MPI_Init and MPI_Init_threads
- MPI_Init_threads is used for programs with threads

ih4cku commented 7 years ago

every collective call is synchronized
MPI_Bcast send the same piece of data to all processes
MPI_Scatter send chunks of an array to different processes
- MPI_Scatter redundant parameters?
For MPI_Gather: the recv_count parameter is the count of elements received per process, not the total summation of counts from all processes

MPI_ALLReduce