Provided by: manpages-dev_2.17-1_all
sched_setaffinity, sched_getaffinity - set and get a process’s CPU
int sched_setaffinity(pid_t pid, unsigned int len, unsigned long
int sched_getaffinity(pid_t pid, unsigned int len, unsigned long
sched_setaffinity() sets the CPU affinity mask of the process denoted
by pid. If pid is zero, then the current process is used.
The affinity mask is represented by the bitmask stored in mask. The
least significant bit corresponds to the first logical processor number
on the system, while the most significant bit corresponds to the last
logical processor number on the system. A set bit corresponds to a
legally schedulable CPU while an unset bit corresponds to an illegally
schedulable CPU. In other words, a process is bound to and will only
run on processors whose corresponding bit is set. Usually, all bits in
the mask are set.
If the process specified by pid is not curently running on one of the
CPUs specified in mask, then that process is migrated to one of the
CPUs specified in mask.
The argument len is the length (in bytes) of the data pointed to by
mask. Normally this is the size of a word on the system. For
compatibility with future versions of the Linux kernel, since this size
can change, the bitmask supplied must be at least as large as the
affinity mask stored in the kernel.
The function sched_getaffinity() writes into the pointer supplied by
mask that has size len the affinity mask of process pid. If pid is
zero, then the mask of the current process is returned.
On success, sched_setaffinity() returns 0. On error, -1 is returned,
and errno is set appropriately.
On success, sched_getaffinity() always returns the size (in bytes) of
the affinity mask used by the kernel. On error, -1 is returned, and
errno is set appropriately.
EFAULT A supplied memory address was invalid.
EINVAL The affinity bitmask mask contains no processors that are
physically on the system, or the length len is smaller than the
size of the affinity mask used by the kernel.
EPERM The calling process does not have appropriate privileges. The
process calling sched_setaffinity() needs an effective user ID
equal to the user ID or effective user ID of the process
identified by pid, or it must possess the CAP_SYS_NICE
ESRCH The process whose ID is pid could not be found.
The affinity mask is actually a per-thread attribute that can be
adjusted independently for each of the threads in a thread group. The
value returned from a call to gettid(2) can be passed in the argument
The affinity syscalls were introduced in Linux kernel 2.5.8. The
library calls were introduced in glibc 2.3, and are still in glibc
2.3.2. Later glibc 2.3.2 development versions changed this interface to
one without the len field, and still later versions reverted again. The
glibc prototype is now
/* Set the CPU affinity for a task */
extern int sched_setaffinity (pid_t pid, size_t cpusetsize,
const cpu_set_t *cpuset);
/* Get the CPU affinity for a task */
extern int sched_getaffinity (pid_t pid, size_t cpusetsize,
clone(2), getpriority(2), gettid(2), nice(2),
sched_getscheduler(2), sched_setscheduler(2), setpriority(2),
sched_setscheduler(2) has a description of the Linux scheduling scheme.