.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk .\" .\" .\" %%%LICENSE_START(VERBATIM) .\" 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 .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date.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. .\" %%%LICENSE_END .\" .TH PTHREAD_SETAFFINITY_NP 3 2016-12-12 "Linux" "Linux Programmer's Manual" .SH NAME pthread_setaffinity_np, pthread_getaffinity_np \- set/get CPU affinity of a thread .SH SYNOPSIS .nf .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" .B #include .BI "int pthread_setaffinity_np(pthread_t " thread ", size_t " cpusetsize , .BI " const cpu_set_t *" cpuset ); .BI "int pthread_getaffinity_np(pthread_t " thread ", size_t " cpusetsize , .BI " cpu_set_t *" cpuset ); .sp Compile and link with \fI\-pthread\fP. .fi .SH DESCRIPTION The .BR pthread_setaffinity_np () function sets the CPU affinity mask of the thread .I thread to the CPU set pointed to by .IR cpuset . If the call is successful, and the thread is not currently running on one of the CPUs in .IR cpuset , then it is migrated to one of those CPUs. The .BR pthread_getaffinity_np () function returns the CPU affinity mask of the thread .I thread in the buffer pointed to by .IR cpuset . For more details on CPU affinity masks, see .BR sched_setaffinity (2). For a description of a set of macros that can be used to manipulate and inspect CPU sets, see .BR CPU_SET (3). The argument .I cpusetsize is the length (in bytes) of the buffer pointed to by .IR cpuset . Typically, this argument would be specified as .IR sizeof(cpu_set_t) . (It may be some other value, if using the macros described in .BR CPU_SET (3) for dynamically allocating a CPU set.) .SH RETURN VALUE On success, these functions return 0; on error, they return a nonzero error number. .SH ERRORS .TP .B EFAULT A supplied memory address was invalid. .TP .B EINVAL .RB ( pthread_setaffinity_np ()) The affinity bit mask .I 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 .BR cpuset (7). .TP .BR EINVAL .RB ( pthread_setaffinity_np ()) .I cpuset specified a CPU that was outside the set supported by the kernel. (The kernel configuration option .BR CONFIG_NR_CPUS defines the range of the set supported by the kernel data type .\" cpumask_t used to represent CPU sets.) .\" The raw sched_getaffinity() system call returns the size (in bytes) .\" of the cpumask_t type. .TP .B EINVAL .RB ( pthread_getaffinity_np ()) .I cpusetsize is smaller than the size of the affinity mask used by the kernel. .TP .B ESRCH No thread with the ID .I thread could be found. .SH VERSIONS These functions are provided by glibc since version 2.3.4. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lbw25 lb lb l l l. Interface Attribute Value T{ .BR pthread_setaffinity_np (), .BR pthread_getaffinity_np () T} Thread safety MT-Safe .TE .SH CONFORMING TO These functions are nonstandard GNU extensions; hence the suffix "_np" (nonportable) in the names. .SH NOTES After a call to .BR pthread_setaffinity_np (), the set of CPUs on which the thread will actually run is the intersection of the set specified in the .I 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 .BR 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 .BR sched_setaffinity (2) and .BR sched_getaffinity (2) system calls. In glibc 2.3.3 only, versions of these functions were provided that did not have a .I cpusetsize argument. Instead the CPU set size given to the underlying system calls was always .IR sizeof(cpu_set_t) . A new thread created by .BR pthread_create (3) inherits a copy of its creator's CPU affinity mask. .SH EXAMPLE In the following program, the main thread uses .BR 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 .BR pthread_getaffinity_np () to check the resulting CPU affinity mask of the thread. .nf #define _GNU_SOURCE #include #include #include #include #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); } .fi .SH SEE ALSO .BR sched_setaffinity (2), .BR CPU_SET (3), .BR pthread_attr_setaffinity_np (3), .BR pthread_self (3), .BR sched_getcpu (3), .BR cpuset (7), .BR pthreads (7), .BR sched (7) .SH COLOPHON This page is part of release 4.10 of the Linux .I 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/.