GOMP_CPU_AFFINITY – Bind threads to specific CPUs#
- Description:
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 the list.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 functions, e.g.,
getenv
in C orGET_ENVIRONMENT_VARIABLE
in Fortran, may be used to query the setting of theGOMP_CPU_AFFINITY
environment variable. A defined CPU affinity on startup cannot be changed or disabled during the runtime of the application.If both
GOMP_CPU_AFFINITY
andOMP_PROC_BIND
are set,OMP_PROC_BIND
has a higher precedence. If neither has been set andOMP_PROC_BIND
is unset, or whenOMP_PROC_BIND
is set toFALSE
, the host system will handle the assignment of threads to CPUs.- See also:
OMP_PLACES – Specifies on which CPUs the theads should be placed, OMP_PROC_BIND – Whether theads may be moved between CPUs