[mpich-discuss] Using MPI_Comm_split to MPI_COMM_LOCAL

[John Bent]

All,

We'd like to create an MPI Communicator for just the processes on each
local node (i.e. something like MPI_COMM_LOCAL).  We were doing this
previously very naively by having everyone send out their hostnames and
then doing string parsing.  We realize that a much simpler way to do it
would be to use MPI_Comm_split to split MPI_COMM_WORLD by the IP
address.  Unfortunately, the IP address is 64 bits and the max "color"
to pass to MPI_Comm_split is only 2^16.  So we're currently planning on
splitting iteratively on each 16 bits in the 64 bit IP address.

Anyone know a better way to achieve MPI_COMM_LOCAL?  Or can
MPI_Comm_split be enhanced to take a 64 bit color?
-- 
Thanks,

John