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"
binds 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 starts 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 or GET_ENVIRONMENT_VARIABLE
in
Fortran, may be used to query the setting of the GOMP_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
and 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 handles the assignment of threads to CPUs.
OMP_PLACES
– Specifies on which CPUs the threads should be placed, OMP_PROC_BIND
– Whether threads may be moved between CPUs