How to determine MPI rank/process number local to a socket/node
It depends on the MPI implementation - and there is no standard for this particular problem.
Open MPI has some environment variables that can help. OMPI_COMM_WORLD_LOCAL_RANK will give you the local rank within a node - ie. this is the process number which you are looking for. A call to getenv will therefore answer your problem - but this is not portable to other MPI implementations.
See this for the (short) list of variables in OpenMPI.
I don't know of a corresponding "node number".
This exact problem is discussed on Markus Wittmann's Blog, MPI Node-Local Rank determination.
There, three strategies are suggested:
- A naive, portable solution employs MPI_Get_processor_name or gethostname to create an unique identifier for the node and performs an MPI_Alltoall on it. [...]
- [Method 2] relies on MPI_Comm_split, which provides an easy way to split a communicator into subgroups (sub-communicators). [...]
- Shared memory can be utilized, if available. [...]
For some working code (presumably LGPL licensed?), Wittmann links to MpiNodeRank.cpp from the APSM library.
I believe you can achieve that with MPI-3 in this manner:
MPI_Comm shmcomm;
MPI_Comm_split_type(MPI_COMM_WORLD, MPI_COMM_TYPE_SHARED, 0,
MPI_INFO_NULL, &shmcomm);
int shmrank;
MPI_Comm_rank(shmcomm, &shmrank);