MPIR_BCAST_BLOCK_SIZE

[l***@yahoo.com]

Hi,
I've read that "MPIR_BCAST_BLOCK_SIZE determines the size of blocks"
in MPI_Bcast. So what is the default value of MPIR_BCAST_BLOCK_SIZE
and how do I change it?

Thank you.

Regards,
Rayne

[Michael Hofmann]

Post by l***@yahoo.com
I've read that "MPIR_BCAST_BLOCK_SIZE determines the size of blocks"
in MPI_Bcast.

Yes, but _only_ for MPICH1 (and maybe its derivatives).

Post by l***@yahoo.com
So what is the default value of MPIR_BCAST_BLOCK_SIZE

from "mpich-1.2.7p1/src/coll/coll.h"

/*
Block sizes for various collective operations

For most systems, a size of 1 is optimal. The claim has been made that
for the SP1, 3 is better. Experiments disagree.

NOTE THAT THIS MUST BE DISABLED FOR HETEROGENEOUS SYSTEMS
*/
#define MPIR_BCAST_BLOCK_SIZE 1

Post by l***@yahoo.com
and how do I change it?

Change the source (e.g. "#define MPIR_BCAST_BLOCK_SIZE 2501") and [re]compile your own MPICH.


Michael