PTHREAD_SETAFFINITY_NP(3) Linux Programmer's Manual PTHREAD_SETAFFINITY_NP(3)NAME
pthread_setaffinity_np, pthread_getaffinity_np - set/get CPU affinity
of a thread
SYNOPSIS
#define _GNU_SOURCE
#include <pthread.h>
int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize,
const cpu_set_t *cpuset);
int pthread_getaffinity_np(pthread_t thread, size_t cpusetsize,
cpu_set_t *cpuset);
Compile and link with -pthread.
DESCRIPTION
The pthread_setaffinity_np() function sets the CPU affinity mask of the
thread thread to the CPU set pointed to by cpuset. If the call is suc‐
cessful, and the thread is not currently running on one of the CPUs in
cpuset, then it is migrated to one of those CPUs.
The pthread_getaffinity_np() function returns the CPU affinity mask of
the thread thread in the buffer pointed to by cpuset.
For more details on CPU affinity masks, see sched_setaffinity(2). For
a description of a set of macros that can be used to manipulate and
inspect CPU sets, see CPU_SET(3).
The argument cpusetsize is the length (in bytes) of the buffer pointed
to by cpuset. Typically, this argument would be specified as
sizeof(cpu_set_t). (It may be some other value, if using the macros
described in CPU_SET(3) for dynamically allocating a CPU set.)
RETURN VALUE
On success, these functions return 0; on error, they return a non-zero
error number.
ERRORS
EFAULT A supplied memory address was invalid.
EINVAL (pthread_setaffinity_np()) The affinity bit mask mask contains
no processors that are currently physically on the system and
permitted to the thread according to any restrictions that may
be imposed by the "cpuset" mechanism described in cpuset(7).
EINVAL (pthread_setaffinity_np()) cpuset specified a CPU that was out‐
side the set supported by the kernel. (The kernel configuration
option CONFIG_NR_CPUS defines the range of the set supported by
the kernel data type used to represent CPU sets.)
EINVAL (pthread_getaffinity_np()) cpusetsize is smaller than the size
of the affinity mask used by the kernel.
ESRCH No thread with the ID thread could be found.
VERSIONS
These functions are provided by glibc since version 2.3.4.
CONFORMING TO
These functions are non-standard GNU extensions; hence the suffix "_np"
(non-portable) in the names.
NOTES
After a call to pthread_setaffinity_np(), the set of CPUs on which the
thread will actually run is the intersection of the set specified in
the cpuset argument and the set of CPUs actually present on the system.
The system may further restrict the set of CPUs on which the thread
runs if the "cpuset" mechanism described in cpuset(7) is being used.
These restrictions on the actual set of CPUs on which the thread will
run are silently imposed by the kernel.
These functions are implemented on top of the sched_setaffinity(2) and
sched_getaffinity(2) system calls.
In glibc 2.3.3 only, versions of these functions were provided that did
not have a cpusetsize argument. Instead the CPU set size given to the
underlying system calls was always sizeof(cpu_set_t).
A new thread created by pthread_create() inherits a copy of its cre‐
ator's CPU affinity mask.
EXAMPLE
In the following program, the main thread uses pthread_setaffinity_np()
to set its CPU affinity mask to include CPUs 0 to 7 (which may not all
be available on the system), and then calls pthread_getaffinity_np() to
check the resulting CPU affinity mask of the thread.
#define _GNU_SOURCE
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#define handle_error_en(en, msg) \
do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
int
main(int argc, char *argv[])
{
int s, j;
cpu_set_t cpuset;
pthread_t thread;
thread = pthread_self();
/* Set affinity mask to include CPUs 0 to 7 */
CPU_ZERO(&cpuset);
for (j = 0; j < 8; j++)
CPU_SET(j, &cpuset);
s = pthread_setaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
if (s != 0)
handle_error_en(s, "pthread_setaffinity_np");
/* Check the actual affinity mask assigned to the thread */
s = pthread_getaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
if (s != 0)
handle_error_en(s, "pthread_getaffinity_np");
printf("Set returned by pthread_getaffinity_np() contained:\n");
for (j = 0; j < CPU_SETSIZE; j++)
if (CPU_ISSET(j, &cpuset))
printf(" CPU %d\n", j);
exit(EXIT_SUCCESS);
}
SEE ALSOsched_getcpu(3), sched_setaffinity(2), sched_setscheduler(2),
pthread_attr_setaffinity_np(3), pthread_self(3), cpuset(7), pthreads(7)COLOPHON
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2008-11-27 PTHREAD_SETAFFINITY_NP(3)
