On Jun 5, 2016, at 12:03 PM, Alexander Droste wrote: > Hi everyone, > > I'd like to know what the maximum buffer size > for sends/receives is. Besides the count being limited > to INT_MAX, how is the max buffer size limited? > > Best regards, > Alex >
Hi Alexander As far as I know, the usual solution to circumvent this type of large count problem is to declare an MPI user type to hold a large number of MPI native types (say, an MPI_Type_Contiguous or MPI_Type_Vector to hold a bunch of floating point numbers). https://www.open-mpi.org/doc/v1.8/man3/MPI_Type_contiguous.3.php Also, an OMPI pro may correct me for saying foolish things on the list, but AFAIK, not all sends/receives are buffered, and the buffer size is set by the default eager/rendevous message threshold (or the value that you set it to be at runtime with OMPI mca parameters). That buffer size may also vary according to the btl (sm,vader, tcp, openib, etc). Search for "eager" and "rendevous" on the FAQ: https://www.open-mpi.org/faq/?category=all I hope this helps, Gus Correa
