Thanks Pavan ! Bibrak Qamar On Thu, Mar 13, 2014 at 3:54 PM, Balaji, Pavan <[email protected]> wrote:

Yes, the tag UB is correct. MPICH reserves one of the tag bits to help with internal fault information propagation.

-- Pavan

On Mar 13, 2014, at 1:30 AM, Bibrak Qamar <[email protected]> wrote:

...

I am trying to get the value of MPI_TAG_UB using the following code:

MPI_Aint * maxTag;; int error, flag;

error = MPI_Comm_get_attr(MPI_COMM_WORLD, MPI_TAG_UB, &maxTag, &flag);

if(error != MPI_SUCCESS || !flag ){ printf( " ERROR IN native mpitagub\n"); }

printf( "mpitagub = %d\n", *maxTag);

For MPICH3 I get

mpitagub = 1073741823

I also did it for OpenMPI and I get

mpitagub = 2147483647

The value from OpenMPI makes sense since its 2^31 -1. But at the end the MPI_TAG_UB is MPI implementation dependent.

So I was wondering the value that I got from MPICH3 (mpitagub = 1073741823) is this OK? or my code is wrong somewhere?

Thanks Bibrak

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