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Subject: Re: [OMPI users] Limitation of MPI_BCAST
From: George Bosilca (bosilca_at_[hidden])
Date: 2013-04-11 18:19:12


Yes, but it is a little more tricky than calling MPI_Bcast.

The prototype of MPI_Bcast as defined by the MPI standard is:
 
> int MPI_Bcast(void* buffer, int count, MPI_Datatype datatype, int root,
> MPI_Comm comm)

This clearly prevents you from using a count larger than MAX_INT. However, you can build a datatype, by composing several types with counts under 1G and then use this datatype to do the bcast.

  George.

On Apr 12, 2013, at 00:11 , William Au <au_wai_chung_at_[hidden]> wrote:

> Hi,
>
> I am using openmpi 1.6 and when I tried to send a large array through MPI_BCAST
> in fortran. The number of count is larger than 3 billions. Although I compiled openmpi and
> my code with the option to declare my fortran integer as 64 bit long in linux. I found out
> that fortran pbcast_f.c will cast my *count to integer to call the c code MPI_Bcast
>
> *ierr = OMPI_INT_2_FINT(MPI_Bcast(OMPI_F2C_BOTTOM(buffer),
> OMPI_FINT_2_INT(*count),
>
> So my question is, is it possible to bcast more than MAX_INT count of data_type in
> openmpi?
>
> Thanks.
>
> Regards,
>
> William
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