GOMP_CPU_AFFINITY– Bind threads to specific CPUs
Binds threads to specific CPUs. The variable should contain a space-separated
or comma-separated list of CPUs. This list may contain different kinds of
entries: either single CPU numbers in any order, a range of CPUs (M-N)
or a range with some stride (M-N:S). CPU numbers are zero based. For example,
GOMP_CPU_AFFINITY="0 3 1-2 4-15:2" will bind the initial thread
to CPU 0, the second to CPU 3, the third to CPU 1, the fourth to
CPU 2, the fifth to CPU 4, the sixth through tenth to CPUs 6, 8, 10, 12,
and 14 respectively and then start assigning back from the beginning of
GOMP_CPU_AFFINITY=0 binds all threads to CPU 0.
There is no libgomp library routine to determine whether a CPU affinity
specification is in effect. As a workaround, language-specific library
getenv in C or
Fortran, may be used to query the setting of the
environment variable. A defined CPU affinity on startup cannot be changed
or disabled during the runtime of the application.
OMP_PROC_BIND are set,
OMP_PROC_BIND has a higher precedence. If neither has been set and
OMP_PROC_BIND is unset, or when
OMP_PROC_BIND is set to
FALSE, the host system will handle the assignment of threads to CPUs.