SCHED_SETAFFINITY(2) Linux Programmer's Manual SCHED_SETAFFINITY(2)
NAME
sched_setaffinity, sched_getaffinity - set and get a process's CPU
affinity mask
SYNOPSIS
#include<sched.h>
intsched_setaffinity(pid_t pid,unsignedint len,unsignedlong
*mask);
intsched_getaffinity(pid_t pid,unsignedint len,unsignedlong
*mask);
DESCRIPTION
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.
The argument len is the length of the data pointed to by mask. Nor-
mally 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 is size len the affinity mask of process pid. If pid is zero,
then the mask of the current process is returned.
RETURNVALUE
On success, sched_setaffinity and sched_getaffinity both return 0. On
error, -1 is returned, and errno is set appropriately.
ERRORS
EFAULT A supplied memory address was invalid.
ESRCH The process whose ID is pid could not be found.
EPERM The calling process does not have appropriate privileges. The
process calling sched_setaffinity needs an effective uid equal
to the euid or uid of the process identified by pid, or it
posses the CAP_SYS_NICE capability.
EINVAL The affinity bitmask mask contains no processors that are physi-
cally on the system or the length len is smaller than the size
of the affinity mask used by the kernel.
HISTORY
The affinity syscalls were introduced in Linux kernel 2.5.8.
SEEALSO
sched_setscheduler(2), sched_getscheduler(2), sched_get_prior-
ity_max(2), sched_get_priority_min(2), nice(2), setpriority(2),
getpriority(2),
sched_setscheduler(2) has a description of the Linux scheduling scheme.
Linux 2002-11-19 SCHED_SETAFFINITY(2)
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