These are very different algorithms, so performance might differ (greatly) for example, MPI_Bcast on root rank can MPI_Send() and return, if the message is short, this is likely an eager send which is very fast. that means MPI_Bcast() returns before all ranks received the data, or even entered MPI_Bcast.
On the other hand, MPI_Barrier() cannot return before all ranks entered the barrier. also, you might find https://github.com/open-mpi/ompi/issues/1713 useful. Cheers, Gilles On Monday, May 30, 2016, Saliya Ekanayake <esal...@gmail.com> wrote: > Hi, > > I ran Ohio micro benchmarks for openmpi and noticed broadcast with smaller > number of bytes is faster than a barrier - 2us vs 120us. > > I'm trying to understand how this could happen? > > Thank you > Saliya >
