threads, cores
and sockets can be optionally followed by a positive number in
parentheses, which denotes the how many places shall be created. With
threads each place corresponds to a single hardware thread; cores
to a single core with the corresponding number of hardware threads; and with
sockets the place corresponds to a single socket. The resulting
placement can be shown by setting the OMP_DISPLAY_ENV environment
variable.
Alternatively, the placement can be specified explicitly as comma-separated
list of places. A place is specified by set of nonnegative numbers in curly
braces, denoting the denoting the hardware threads. The hardware threads
belonging to a place can either be specified as comma-separated list of
nonnegative thread numbers or using an interval. Multiple places can also be
either specified by a comma-separated list of places or by an interval. To
specify an interval, a colon followed by the count is placed after after
the hardware thread number or the place. Optionally, the length can be
followed by a colon and the stride number – otherwise a unit stride is
assumed. For instance, the following specifies the same places list:
"{0,1,2}, {3,4,6}, {7,8,9}, {10,11,12}";
"{0:3}, {3:3}, {7:3}, {10:3}"; and "{0:2}:4:3".
If OMP_PLACES and GOMP_CPU_AFFINITY are unset and
OMP_PROC_BIND is either unset or false, threads may be moved
between CPUs following no placement policy.