How to I determine the local node placement of tasks in MPI - fortran

Question

I have a basic program that I am trying to run to determine where MPI will place a task given that the number of tasks is greater than the number of available processors (oversubscribing). If I run, for example, mpirun -np <program name> the result will give:
processor 0 of 4
processor 1 of 4
processor 2 of 4
processor 3 of 4
But, if I run the same command on "8" processors I get :
processor 1 of 8
processor 2 of 8
processor 5 of 8
processor 6 of 8
processor 4 of 8
processor 3 of 8
processor 7 of 8
processor 0 of 8
I understand that there are not 8 actual cores running my program and instead I have multiple tasks being run on the same processors and I want to know exactly how these are distributed. Thanks in advance.
edit:
program test
! Similar to "Hello World" example- trying to determine rank/ node placement
use mpi
implicit none
integer :: procid, ierr, numprocs, name_len
integer:: local
local= 'OMPI_COMM_WORLD_LOCAL_RANK'
!character* (MPI_max_processor_name) name
call MPI_INIT(ierr)
call MPI_COMM_SIZE(MPI_COMM_World, numprocs, ierr)
call MPI_COMM_RANK(MPI_COMM_World, procid, ierr)
!call Mpi_Get_Processor_Name(name,name_len, ierr)
print*, 'processor', procid, 'of', numprocs, 'On Local Node:',' ', local
call mpi_finalize(ierr)
end program test

Answer 1

can you post your test program ?
is "processor x of y" coming from MPI_Comm_rank() and MPI_Comm_size() ?
in this case, these numbers are MPI ranks and have nothing to do with binding.
you'd rather read your MPI documentation and figure out how the binding is done.
an other option i sometimes use is (with Open MPI)
mpirun --tag-output grep Cpus_allowed_list /proc/self/status
note there is a possibility no binding is performed when you oversubscribe your nodes.

Answer 2

Unfortunately, it is quite common in MPI to use the same words for different meanings.
For example, job managers tend to mix the word processor and use it for different meanings. In this specific case, I will use the following:
This also applies to MPI_Get_processor_name. The standard does not actually require to return a name uniquely identifying a processor. The name is left to the implementations, which usually tend to report the name of the host. This is not what I assume you are looking for.
I will use the word processor to identify a CPU core or, in an hyperthreading enabled scenario, a hardware thread (although a hardware thread is not exactly a CPU core ).
A regular process (be it MPI or not) is usually allowed to execute on different processors. This does not necessarily mean that the process will use ALL this processors, but rather being able to bounce from one to another if the former is now occupied by a different process (usually due to Operative System scheduler).
To obtain the process affinity (the list of processors that a process can use), you should use a different interface. For example, you can use something like sched_getaffinity (this is C, though). Some MPI implementations such as Intel MPI, allow you to print the process affinity at MPI_Init, setting an environment variable.
I would consider using existing programs that report the affinity. Check this page in the MPICH documentation.
Also included in the MPICH source is a program for printing out the affinity of a process (src/pm/hydra/examples/print_cpus_allowed.c) according to the OS. This can be used on Linux systems to test that bindings are working correctly.
shell$ mpiexec -n 8 -bind-to socket ./print_cpus_allowed | sort
crush[0]: Cpus_allowed_list: 0,2,4,6
crush[1]: Cpus_allowed_list: 1,3,5,7
crush[2]: Cpus_allowed_list: 0,2,4,6
crush[3]: Cpus_allowed_list: 1,3,5,7
crush[4]: Cpus_allowed_list: 0,2,4,6
crush[5]: Cpus_allowed_list: 1,3,5,7
crush[6]: Cpus_allowed_list: 0,2,4,6
crush[7]: Cpus_allowed_list: 1,3,5,7