DOKK / manpages / debian 13 / openmpi-doc / OMPI_Affinity_str.openmpi.3.en
OMPI_AFFINITY_STR(3) Open MPI OMPI_AFFINITY_STR(3)

OMPI_Affinity_str - Obtain prettyprint strings of processor affinity information for this process

#include <mpi.h>
#include <mpi-ext.h>
int OMPI_Affinity_str(ompi_affinity_fmt_type_t fmt_type,


                      char ompi_bound[OMPI_AFFINITY_STRING_MAX],


                      char current_binding[OMPI_AFFINITY_STRING_MAX],


                      char exists[OMPI_AFFINITY_STRING_MAX])


There is no Fortran binding for this function.

There is no Fortran 2008 binding for this function.

There is no C++ binding for this function.

  • fmt_type: An enum indicating how to format the returned ompi_bound and current_binding strings. OMPI_AFFINITY_RSRC_STRING_FMT returns the string as human-readable resource names, such as “socket 0, core 0”.
  • OMPI_AFFINITY_LAYOUT_FMT returns ASCII art representing where this MPI: process is bound relative to the machine resource layout. For example “[. B][. .]” shows the process that called the routine is bound to socket 0, core 1 in a system with 2 sockets, each containing 2 cores.
  • See below for more output examples.:

  • ompi_bound: A prettyprint string describing what processor(s) Open MPI bound this process to, or a string indicating that Open MPI did not bind this process.
  • current_binding: A prettyprint string describing what processor(s) this process is currently bound to, or a string indicating that the process is bound to all available processors (and is therefore considered “unbound”).
  • exists: A prettyprint string describing the available sockets and sockets on this host.

Open MPI may bind a process to specific sockets and/or cores at process launch time. This non-standard Open MPI function call returns prettyprint information about three things:

The string returned in ompi_bound will either indicate that Open MPI did not bind this process to anything, or it will contain a prettyprint description of the processor(s) to which Open MPI bound this process.
Regardless of whether Open MPI bound this process or not, another entity may have bound it. The string returned in current_binding will indicate what the current binding is of this process, regardless of what Open MPI may have done earlier. The string returned will either indicate that the process is unbound (meaning that it is bound to all available processors) or it will contain a prettyprint description of the sockets and cores to which the process is currently bound.
As a convenience to the user, the exists string will contain a prettyprint description of the sockets and cores that this process can see (which is usually all processors in the system).

Example 1: Print out processes binding using resource string format.

int rank;
char ompi_bound[OMPI_AFFINITY_STRING_MAX];
char current_binding[OMPI_AFFINITY_STRING_MAX];
char exists[OMPI_AFFINITY_STRING_MAX];
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
OMPI_Affinity_str(OMPI_AFFINITY_RSRC_STRING_FMT,


                  ompi_bound, current_binding, exists);
printf("rank %d: \n"


       "       ompi_bound: %s\n"


       "  current_binding: %s\n"


       "           exists: %s\n",


       rank, ompi_bound, current_binding, exists);
...


Output of mpirun -n 2 -bind-to-core a.out:

rank 0:


       ompi_bound: socket 0[core 0]


  current_binding: socket 0[core 0]


           exists: socket 0 has 4 cores
rank 1:


       ompi_bound: socket 0[core 1]


  current_binding: socket 0[core 1]


           exists: socket 0 has 4 cores


Output of mpirun -n 2 -bind-to-socket a.out:

rank 0:


       ompi_bound: socket 0[core 0-3]


  current_binding: Not bound (or bound to all available processors)


           exists: socket 0 has 4 cores
rank 1:


       ompi_bound: socket 0[core 0-3]


  current_binding: Not bound (or bound to all available processors)


           exists: socket 0 has 4 cores



Example 2: Print out processes binding using layout string format.

int rank;
char ompi_bound[OMPI_AFFINITY_STRING_MAX];
char current_binding[OMPI_AFFINITY_STRING_MAX];
char exists[OMPI_AFFINITY_STRING_MAX];
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
OMPI_Affinity_str(OMPI_AFFINITY_LAYOUT_FMT,


                  ompi_bound, current_binding, exists);
printf("rank %d: \n"


       "       ompi_bound: %s\n"


       "  current_binding: %s\n"


       "           exists: %s\n",


       rank, ompi_bound, current_binding, exists);
...


Output of mpirun -n 2 -bind-to-core a.out:

rank 0:


       ompi_bound: [B . . .]


  current_binding: [B . . .]


           exists: [. . . .]
rank 1:


       ompi_bound: [. B . .]


  current_binding: [. B . .]


           exists: [. . . .]


Output of mpirun -n 2 -bind-to-socket a.out:

rank 0:


       ompi_bound: [B B B B]


  current_binding: [B B B B]


           exists: [. . . .]
rank 1:


       ompi_bound: [B B B B]


  current_binding: [B B B B]


           exists: [. . . .]


SEE ALSO:

mpirun(1)


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February 17, 2025