PTHREAD_SETAFFINITY_NP
Section: Linux Programmer's Manual (3)
Updated: 2021-03-22
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NAME
pthread_setaffinity_np, pthread_getaffinity_np - set/get
CPU affinity of a thread
SYNOPSIS
#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.
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 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.)
RETURN VALUE
On success, these functions return 0;
on error, they return a nonzero 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 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.
VERSIONS
These functions are provided by glibc since version 2.3.4.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
Interface | Attribute | Value
|
pthread_setaffinity_np(),
pthread_getaffinity_np()
| Thread safety | MT-Safe
|
CONFORMING TO
These functions are nonstandard GNU extensions;
hence the suffix "_np" (nonportable) 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(3)
inherits a copy of its creator's CPU affinity mask.
EXAMPLES
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;
cpu_set_t cpuset;
pthread_t thread;
thread = pthread_self();
/* Set affinity mask to include CPUs 0 to 7. */
CPU_ZERO(&cpuset);
for (int j = 0; j < 8; j++)
CPU_SET(j, &cpuset);
s = pthread_setaffinity_np(thread, sizeof(cpuset), &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(cpuset), &cpuset);
if (s != 0)
handle_error_en(s, "pthread_getaffinity_np");
printf("Set returned by pthread_getaffinity_np() contained:\n");
for (int j = 0; j < CPU_SETSIZE; j++)
if (CPU_ISSET(j, &cpuset))
printf(" CPU %d\n", j);
exit(EXIT_SUCCESS);
}
SEE ALSO
sched_setaffinity(2),
CPU_SET(3),
pthread_attr_setaffinity_np(3),
pthread_self(3),
sched_getcpu(3),
cpuset(7),
pthreads(7),
sched(7)
COLOPHON
This page is part of release 5.11 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- EXAMPLES
-
- SEE ALSO
-
- COLOPHON
-
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Time: 06:22:48 GMT, May 09, 2021