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) ; |
![]() |
Note |
---|---|
Compile and link with |
The pthread_setaffinity_np
()
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
.
The argument cpusetsize
is the length (in
bytes) of the buffer pointed to by cpuset
. Normally this argument
would be specified as sizeof(cpu_set_t)
. The
constant CPU_SETSIZE
specifies
a value one greater than the maximum CPU number that can be
stored in a CPU set.
For more details on CPU affinity masks, as well as a description of a set of macros that can be used to manipulate and inspect CPU sets, see sched_setaffinity(2) for details.
A supplied memory address was invalid.
(pthread_setaffinity_np
()) The
affinity bit mask mask
contains no processors that are physically on the
system.
(pthread_setaffinity_np
()) cpuset
specified a CPU
that was outside the range permitted by the kernel data
type used to represent CPU sets. This range is
determined by the kernel configuration option
CONFIG_NR_CPUS
.
(pthread_getaffinity_np
()) cpusetsize
is smaller
than the size of the affinity mask used by the
kernel.
There is no thread matching thread
(e.g., perhaps
that thread has already terminated and been
joined).
These functions are non-standard GNU extensions; hence the suffix "_np" (non-portable) in the names.
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 errExitEN(en, msg) { errno = en; perror(msg); \ exit(EXIT_FAILURE); } 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) errExitEN(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) errExitEN(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 3.12 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/.
Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk <mtk.manpagesgmail.com> Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. |