[Dune-devel] Long MPI startup

[Markus Blatt]

Hi,


On Fri, Dec 11, 2020 at 12:19:56PM +0100, Oliver Sander wrote:
> 
> I recently noticed that on my system (current Debian testing), the call to
> 
>   MPIHelper::instance(argc, argv);
> 
> takes between 2 and 3 seconds to complete.  This seems like a long time to me.
> Is it to be expected?  Or is there a bug somewhere?

I don't think that we do anything specical during startup (besides calling
MPI_Init). Hence I doubt that this is a Dune problem.

Maybe you cound try a minimal MPI program to compare?

#include <mpi.h>
#include <iosteam>

int main(int argc, char** argv){
  MPI_Init(&argc, argv);
  int size, rank;
  MPI_Comm_size(&size, MPI_COMM_WORLD);
  MPI_Comm_rank(&rank, MPI_COMM_WORLD);
  //Above should be all that DUNE does
  std::cout<<"Hi, I am rank "<<rank<<" of "<<size<<"."<<std::endl;
  MPI_Finalize();
  return 0;
}

BTW on my multicore machine (32 cores) it takes some time, too.
Mabe you have a new machine? What MPI?

HTH,

Markus

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