1PTHREAD_SETAFFINITY_NP(3) Linux Programmer's Manual PTHREAD_SETAFFINITY_NP(3)
2
6 pthread_setaffinity_np, pthread_getaffinity_np - set/get CPU affinity
7 of a thread
8
10 #define _GNU_SOURCE /* See feature_test_macros(7) */
11 #include <pthread.h>
12 int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize,
14 const cpu_set_t *cpuset);
15 int pthread_getaffinity_np(pthread_t thread, size_t cpusetsize,
16 cpu_set_t *cpuset);
17 Compile and link with -pthread.
19
21 The pthread_setaffinity_np() function sets the CPU affinity mask of the
22 thread thread to the CPU set pointed to by cpuset. If the call is suc‐
23 cessful, and the thread is not currently running on one of the CPUs in
24 cpuset, then it is migrated to one of those CPUs.
25 The pthread_getaffinity_np() function returns the CPU affinity mask of
27 the thread thread in the buffer pointed to by cpuset.
28 For more details on CPU affinity masks, see sched_setaffinity(2). For
30 a description of a set of macros that can be used to manipulate and in‐
31 spect CPU sets, see CPU_SET(3).
32 The argument cpusetsize is the length (in bytes) of the buffer pointed
34 to by cpuset. Typically, this argument would be specified as
35 sizeof(cpu_set_t). (It may be some other value, if using the macros
36 described in CPU_SET(3) for dynamically allocating a CPU set.)
37
39 On success, these functions return 0; on error, they return a nonzero
40 error number.
41
43 EFAULT A supplied memory address was invalid.
44 EINVAL (pthread_setaffinity_np()) The affinity bit mask mask contains
46 no processors that are currently physically on the system and
47 permitted to the thread according to any restrictions that may
48 be imposed by the "cpuset" mechanism described in cpuset(7).
49 EINVAL (pthread_setaffinity_np()) cpuset specified a CPU that was out‐
51 side the set supported by the kernel. (The kernel configuration
52 option CONFIG_NR_CPUS defines the range of the set supported by
53 the kernel data type used to represent CPU sets.)
54 EINVAL (pthread_getaffinity_np()) cpusetsize is smaller than the size
56 of the affinity mask used by the kernel.
57 ESRCH No thread with the ID thread could be found.
59
61 These functions are provided by glibc since version 2.3.4.
62
64 For an explanation of the terms used in this section, see at‐
65 tributes(7).
66 ┌────────────────────────────────────────────┬───────────────┬─────────┐
68 │Interface │ Attribute │ Value │
69 ├────────────────────────────────────────────┼───────────────┼─────────┤
70 │pthread_setaffinity_np(), │ Thread safety │ MT-Safe │
71 │pthread_getaffinity_np() │ │ │
72 └────────────────────────────────────────────┴───────────────┴─────────┘
73
75 These functions are nonstandard GNU extensions; hence the suffix "_np"
76 (nonportable) in the names.
77
79 After a call to pthread_setaffinity_np(), the set of CPUs on which the
80 thread will actually run is the intersection of the set specified in
81 the cpuset argument and the set of CPUs actually present on the system.
82 The system may further restrict the set of CPUs on which the thread
83 runs if the "cpuset" mechanism described in cpuset(7) is being used.
84 These restrictions on the actual set of CPUs on which the thread will
85 run are silently imposed by the kernel.
86 These functions are implemented on top of the sched_setaffinity(2) and
88 sched_getaffinity(2) system calls.
89 In glibc 2.3.3 only, versions of these functions were provided that did
91 not have a cpusetsize argument. Instead the CPU set size given to the
92 underlying system calls was always sizeof(cpu_set_t).
93 A new thread created by pthread_create(3) inherits a copy of its cre‐
95 ator's CPU affinity mask.
96
98 In the following program, the main thread uses pthread_setaffinity_np()
99 to set its CPU affinity mask to include CPUs 0 to 7 (which may not all
100 be available on the system), and then calls pthread_getaffinity_np() to
101 check the resulting CPU affinity mask of the thread.
102 #define _GNU_SOURCE
104 #include <pthread.h>
105 #include <stdio.h>
106 #include <stdlib.h>
107 #include <errno.h>
108 #define handle_error_en(en, msg) \
110 do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
111 int
113 main(int argc, char *argv[])
114 {
115 int s;
116 cpu_set_t cpuset;
117 pthread_t thread;
118 thread = pthread_self();
120 /* Set affinity mask to include CPUs 0 to 7. */
122 CPU_ZERO(&cpuset);
124 for (int j = 0; j < 8; j++)
125 CPU_SET(j, &cpuset);
126 s = pthread_setaffinity_np(thread, sizeof(cpuset), &cpuset);
128 if (s != 0)
129 handle_error_en(s, "pthread_setaffinity_np");
130 /* Check the actual affinity mask assigned to the thread. */
132 s = pthread_getaffinity_np(thread, sizeof(cpuset), &cpuset);
134 if (s != 0)
135 handle_error_en(s, "pthread_getaffinity_np");
136 printf("Set returned by pthread_getaffinity_np() contained:\n");
138 for (int j = 0; j < CPU_SETSIZE; j++)
139 if (CPU_ISSET(j, &cpuset))
140 printf(" CPU %d\n", j);
141 exit(EXIT_SUCCESS);
143 }
144
146 sched_setaffinity(2), CPU_SET(3), pthread_attr_setaffinity_np(3),
147 pthread_self(3), sched_getcpu(3), cpuset(7), pthreads(7), sched(7)
148
150 This page is part of release 5.13 of the Linux man-pages project. A
151 description of the project, information about reporting bugs, and the
152 latest version of this page, can be found at
153 https://www.kernel.org/doc/man-pages/.
154Linux 2021-03-22 PTHREAD_SETAFFINITY_NP(3)