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affinity(3) [netbsd man page]

AFFINITY(3)						   BSD Library Functions Manual 					       AFFINITY(3)

pthread_setaffinity_np, pthread_getaffinity_np -- affinity of threads LIBRARY
POSIX Threads Library (libpthread, -lpthread) SYNOPSIS
#include <pthread.h> #include <sched.h> int pthread_setaffinity_np(pthread_t thread, size_t size, cpuset_t *set); int pthread_getaffinity_np(pthread_t thread, size_t size, cpuset_t *set); DESCRIPTION
Thread affinity allows to run the thread on specified CPU or CPUs only. The pthread_setaffinity_np() function sets the affinity mask set for thread. At least one valid CPU must be set in the mask. The pthread_getaffinity_np() function gets the affinity mask of thread into set. Note that set must be created and initialized using the cpuset(3) functions. IMPLEMENTATION NOTES
Setting CPU pthread_setaffinity_np requires super-user privileges. Ordinary users can be allowed to control CPU affinity of their threads via the security.models.extensions.user_set_cpu_affinity sysctl(7). See secmodel_extensions(9). Portable applications should not use the pthread_setaffinity_np() and pthread_getaffinity_np() functions. RETURN VALUES
The pthread_setaffinity_np() and pthread_getaffinity_np() functions return 0 on success. Otherwise, an error number is returned to indicate the error. EXAMPLES
An example of code fragment, which sets the affinity for the current thread to the CPU whose ID is 0: cpuset_t *cset; pthread_t pth; cpuid_t ci; cset = cpuset_create(); if (cset == NULL) { err(EXIT_FAILURE, "cpuset_create"); } ci = 0; cpuset_set(ci, cset); pth = pthread_self(); error = pthread_setaffinity_np(pth, cpuset_size(cset), cset); if (error) { ... } cpuset_destroy(cset); COMPATIBILITY
Both functions are non-standard extensions. ERRORS
Both functions may fail if: [EINVAL] The specified set was invalid. [EPERM] The calling process lacks the appropriate privileges to perform the operation. [ESRCH] No thread could be found corresponding to the one specified by thread. NOTES
There is an alternative processor sets interface, see pset(3). However, thread affinity and processor sets are mutually exclusive, hence mixing of these interfaces is prohibited. SEE ALSO
cpuset(3), pset(3), pthread_getschedparam(3), pthread_setschedparam(3), sched(3), schedctl(8) BSD
December 4, 2011 BSD

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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 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 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 permit- ted 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. 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() inherits a copy of its creator'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: "); for (j = 0; j < CPU_SETSIZE; j++) if (CPU_ISSET(j, &cpuset)) printf(" CPU %d ", j); exit(EXIT_SUCCESS); } SEE ALSO
sched_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 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at Linux 2008-11-27 PTHREAD_SETAFFINITY_NP(3)

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