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     cpuset_getaffinity, cpuset_setaffinity — manage CPU affinity


     Standard C Library (libc, -lc)


     #include <sys/param.h>
     #include <sys/cpuset.h>

     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 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 error.


     The following error codes may be set in errno:

     [EINVAL]           The level or which argument was not a valid value.

     [EINVAL]           The mask argument specified when calling cpuset_setaffinity() 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


     cpuset(1), cpuset(2), cpuset_getid(2), cpuset_setid(2), pthread_affinity_np(3),


     The cpuset_getaffinity family of system calls first appeared in FreeBSD 7.1.


     Jeffrey Roberson <>