What is the time complexity of MPI barriers? Do they scale for large number of cores (>> 10k)?
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What is the time complexity of MPI barriers? Do they scale for large number of cores (>> 10k)?
Barrier complexity is highly implementation-specific. It could be linear, it could be logarithmic, or it could be better or worse. Some architectures provide dedicated networks for some collective operations, e.g. IBM’s Blue Gene has a specialised global interrupt network which allows for very fast
MPI_BARRIERimplementation with almost constant complexity but only when performed overMPI_COMM_WORLD.