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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
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PTHREAD_SETAFFINITY_NP(3) Linux Programmer's ManualPTHREAD_SETAFFINITY_NP(3)
pthread_setaffinity_np, pthread_getaffinity_np - set/get CPU affinity
of a thread
#define _GNU_SOURCE /* See feature_test_macros(7) */
#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 nonzero
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────┼───────────────┼─────────┤
│pthread_setaffinity_np(), │ Thread safety │ MT-Safe │
│pthread_getaffinity_np() │ │ │
└──────────────────────────┴───────────────┴─────────┘
These functions are nonstandard GNU extensions; hence the suffix
"_np" (nonportable) 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(3) 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_setaffinity(2), CPU_SET(3), pthread_attr_setaffinity_np(3),
pthread_self(3), sched_getcpu(3), cpuset(7), pthreads(7), sched(7)
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 PTHREAD_SETAFFINITY_NP(3)
Pages that refer to this page: sched_setaffinity(2), CPU_SET(3), pthread_attr_setaffinity_np(3), sched(7)
Copyright and license for this manual page
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