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cpuset_getaffinity, cpuset_setaffinity — manage CPU affinity
Standard C Library (libc, -lc)
cpuset_getaffinity(cpulevel_t level, cpuwhich_t which, id_t id,
size_t setsize, cpuset_t *mask);
cpuset_setaffinity(cpulevel_t level, cpuwhich_t which, id_t id,
size_t setsize, const cpuset_t *mask);
cpuset_getaffinity() and cpuset_setaffinity() allow the manipulation of
sets of CPUs available to processes, threads, interrupts, jails and other
resources. These functions may manipulate sets of CPUs that contain many
processes or per-object anonymous masks that effect only a single object.
The valid values for the level and which arguments are documented in
cpuset(2). These arguments specify which object and which set of the
object we are referring to. Not all possible combinations are valid.
For example, only processes may belong to a numbered set accessed by a
level argument of CPU_LEVEL_CPUSET. All resources, however, have a mask
which may be manipulated with CPU_LEVEL_WHICH.
Masks of type cpuset_t are composed using the CPU_SET(2) macros. The
kernel tolerates large sets as long as all CPUs specified in the set
exist. Sets smaller than the kernel uses generate an error on calls to
cpuset_getaffinity() even if the result set would fit within the user
supplied set. Calls to cpuset_setaffinity() tolerate small sets with no
The supplied mask should have a size of setsize bytes. This size is
usually provided by calling sizeof(mask) which is ultimately determined
by the value of CPU_SETSIZE as defined in <sys/cpuset.h>.
cpuset_getaffinity() retrieves the mask from the object specified by
level, which and id and stores it in the space provided by mask.
cpuset_setaffinity() attempts to set the mask for the object specified by
level, which and id to the value in mask.
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
The following error codes may be set in errno:
[EINVAL] The level or which argument was not a valid value.
[EDEADLK] The cpuset_setaffinity() call would leave a thread
without a valid CPU to run on because the set does not
overlap with the thread's anonymous mask.
[EFAULT] The mask pointer passed was invalid.
[ESRCH] The object specified by the id and which arguments
could not be found.
[ERANGE] The cpusetsize was either preposterously large or
smaller than the kernel set size.
[EPERM] The calling process did not have the credentials
required to complete the operation.
cpuset(1), cpuset(2), cpuset_getid(2), cpuset_setid(2), CPU_SET(3),
The cpuset_getaffinity family of system calls first appeared in
Jeffrey Roberson ⟨jeff@FreeBSD.org⟩