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 └──────────────────────────┴───────────────┴─────────┘
74 These functions are nonstandard GNU extensions; hence the suffix "_np"
75 (nonportable) in the names.
76
78 After a call to pthread_setaffinity_np(), the set of CPUs on which the
79 thread will actually run is the intersection of the set specified in
80 the cpuset argument and the set of CPUs actually present on the system.
81 The system may further restrict the set of CPUs on which the thread
82 runs if the "cpuset" mechanism described in cpuset(7) is being used.
83 These restrictions on the actual set of CPUs on which the thread will
84 run are silently imposed by the kernel.
85 These functions are implemented on top of the sched_setaffinity(2) and
87 sched_getaffinity(2) system calls.
88 In glibc 2.3.3 only, versions of these functions were provided that did
90 not have a cpusetsize argument. Instead the CPU set size given to the
91 underlying system calls was always sizeof(cpu_set_t).
92 A new thread created by pthread_create(3) inherits a copy of its cre‐
94 ator's CPU affinity mask.
95
97 In the following program, the main thread uses pthread_setaffinity_np()
98 to set its CPU affinity mask to include CPUs 0 to 7 (which may not all
99 be available on the system), and then calls pthread_getaffinity_np() to
100 check the resulting CPU affinity mask of the thread.
101 #define _GNU_SOURCE
103 #include <pthread.h>
104 #include <stdio.h>
105 #include <stdlib.h>
106 #include <errno.h>
107 #define handle_error_en(en, msg) \
109 do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
110 int
112 main(int argc, char *argv[])
113 {
114 int s;
115 cpu_set_t cpuset;
116 pthread_t thread;
117 thread = pthread_self();
119 /* Set affinity mask to include CPUs 0 to 7 */
121 CPU_ZERO(&cpuset);
123 for (int j = 0; j < 8; j++)
124 CPU_SET(j, &cpuset);
125 s = pthread_setaffinity_np(thread, sizeof(cpuset), &cpuset);
127 if (s != 0)
128 handle_error_en(s, "pthread_setaffinity_np");
129 /* Check the actual affinity mask assigned to the thread */
131 s = pthread_getaffinity_np(thread, sizeof(cpuset), &cpuset);
133 if (s != 0)
134 handle_error_en(s, "pthread_getaffinity_np");
135 printf("Set returned by pthread_getaffinity_np() contained:\n");
137 for (int j = 0; j < CPU_SETSIZE; j++)
138 if (CPU_ISSET(j, &cpuset))
139 printf(" CPU %d\n", j);
140 exit(EXIT_SUCCESS);
142 }
143
145 sched_setaffinity(2), CPU_SET(3), pthread_attr_setaffinity_np(3),
146 pthread_self(3), sched_getcpu(3), cpuset(7), pthreads(7), sched(7)
147
149 This page is part of release 5.10 of the Linux man-pages project. A
150 description of the project, information about reporting bugs, and the
151 latest version of this page, can be found at
152 https://www.kernel.org/doc/man-pages/.
153Linux 2020-11-01 PTHREAD_SETAFFINITY_NP(3)