NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON
PTHREAD_SETAFFINITY_NP(3) Linux Programmer's Manual PTHREAD_SETAFFINITY_NP(3)
pthread_setaffinity_np, pthread_getaffinity_np - set/get CPU affinity of a
thread
#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.
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 successful, 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.)
On success, these functions return 0; on error, they return a non-zero error
number.
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 outside 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.
These functions are provided by glibc since version 2.3.4.
These functions are non-standard GNU extensions; hence the suffix "_np" (non-
portable) in the names.
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 creator's CPU
affinity mask.
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);
}
sched_getcpu(3), sched_setaffinity(2), sched_setscheduler(2),
pthread_attr_setaffinity_np(3), pthread_self(3), cpuset(7), pthreads(7)
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)