Situating Ourselves
From a programmers perspective, briefly explain the differences between OpenMP and MPI. Explain in your own words why is MPI interesting, if we have already ween OpenMP?
Terminology: Ranks?
Explain what a Rank
is in the MPI world. How does it differ
from processes, threads and nodes?
MPI: Reduction I
Explain why it is important for all processes to call the same
collective operation (e.g.,
MPI_Reduce). What
happens when one process does something else instead?
MPI: Reduction II
Consider the following sequential code, where arr
is an array of size N and elements of
type int:
int max = -1; size_t idx = -1;
for (size_t i = 0; i < N; ++i) {
if (max < arr[i]) {
max = arr[i];
idx = i;
}
}Assume a friend implements a implementation that would implement reduction manually, by sending all values to process 0. What could they have done better, and why?
MPI: Tags
What roles to tags
play in point-to-point and collective
communication?
MPI: Primitives & Derivatives
Show how
using MPI_Recv, MPI_Send, MPI_Comm_size
and MPI_Comm_rank
you implement your own version
of MPI_Scatter?