1CPU_SET(3) Linux Programmer's Manual CPU_SET(3)
2
6 CPU_SET, CPU_CLR, CPU_ISSET, CPU_ZERO, CPU_COUNT, CPU_AND, CPU_OR,
7 CPU_XOR, CPU_EQUAL, CPU_ALLOC, CPU_ALLOC_SIZE, CPU_FREE, CPU_SET_S,
8 CPU_CLR_S, CPU_ISSET_S, CPU_ZERO_S, CPU_COUNT_S, CPU_AND_S, CPU_OR_S,
9 CPU_XOR_S, CPU_EQUAL_S - macros for manipulating CPU sets
10
12 #define _GNU_SOURCE /* See feature_test_macros(7) */
13 #include <sched.h>
14 void CPU_ZERO(cpu_set_t *set);
16 void CPU_SET(int cpu, cpu_set_t *set);
18 void CPU_CLR(int cpu, cpu_set_t *set);
19 int CPU_ISSET(int cpu, cpu_set_t *set);
20 int CPU_COUNT(cpu_set_t *set);
22 void CPU_AND(cpu_set_t *destset,
24 cpu_set_t *srcset1, cpu_set_t *srcset2);
25 void CPU_OR(cpu_set_t *destset,
26 cpu_set_t *srcset1, cpu_set_t *srcset2);
27 void CPU_XOR(cpu_set_t *destset,
28 cpu_set_t *srcset1, cpu_set_t *srcset2);
29 int CPU_EQUAL(cpu_set_t *set1, cpu_set_t *set2);
31 cpu_set_t *CPU_ALLOC(int num_cpus);
33 void CPU_FREE(cpu_set_t *set);
34 size_t CPU_ALLOC_SIZE(int num_cpus);
35 void CPU_ZERO_S(size_t setsize, cpu_set_t *set);
37 void CPU_SET_S(int cpu, size_t setsize, cpu_set_t *set);
39 void CPU_CLR_S(int cpu, size_t setsize, cpu_set_t *set);
40 int CPU_ISSET_S(int cpu, size_t setsize, cpu_set_t *set);
41 int CPU_COUNT_S(size_t setsize, cpu_set_t *set);
43 void CPU_AND_S(size_t setsize, cpu_set_t *destset,
45 cpu_set_t *srcset1, cpu_set_t *srcset2);
46 void CPU_OR_S(size_t setsize, cpu_set_t *destset,
47 cpu_set_t *srcset1, cpu_set_t *srcset2);
48 void CPU_XOR_S(size_t setsize, cpu_set_t *destset,
49 cpu_set_t *srcset1, cpu_set_t *srcset2);
50 int CPU_EQUAL_S(size_t setsize, cpu_set_t *set1, cpu_set_t *set2);
52
54 The cpu_set_t data structure represents a set of CPUs. CPU sets are
55 used by sched_setaffinity(2) and similar interfaces.
56 The cpu_set_t data type is implemented as a bit mask. However, the
58 data structure should be treated as opaque: all manipulation of CPU
59 sets should be done via the macros described in this page.
60 The following macros are provided to operate on the CPU set set:
62 CPU_ZERO()
64 Clears set, so that it contains no CPUs.
65 CPU_SET()
67 Add CPU cpu to set.
68 CPU_CLR()
70 Remove CPU cpu from set.
71 CPU_ISSET()
73 Test to see if CPU cpu is a member of set.
74 CPU_COUNT()
76 Return the number of CPUs in set.
77 Where a cpu argument is specified, it should not produce side effects,
79 since the above macros may evaluate the argument more than once.
80 The first CPU on the system corresponds to a cpu value of 0, the next
82 CPU corresponds to a cpu value of 1, and so on. No assumptions should
83 be made about particular CPUs being available, or the set of CPUs being
84 contiguous, since CPUs can be taken offline dynamically or be otherwise
85 absent. The constant CPU_SETSIZE (currently 1024) specifies a value
86 one greater than the maximum CPU number that can be stored in
87 cpu_set_t.
88 The following macros perform logical operations on CPU sets:
90 CPU_AND()
92 Store the intersection of the sets srcset1 and srcset2 in dest‐
93 set (which may be one of the source sets).
94 CPU_OR()
96 Store the union of the sets srcset1 and srcset2 in destset
97 (which may be one of the source sets).
98 CPU_XOR()
100 Store the XOR of the sets srcset1 and srcset2 in destset (which
101 may be one of the source sets). The XOR means the set of CPUs
102 that are in either srcset1 or srcset2, but not both.
103 CPU_EQUAL()
105 Test whether two CPU set contain exactly the same CPUs.
106 Dynamically sized CPU sets
108 Because some applications may require the ability to dynamically size
109 CPU sets (e.g., to allocate sets larger than that defined by the stan‐
110 dard cpu_set_t data type), glibc nowadays provides a set of macros to
111 support this.
112 The following macros are used to allocate and deallocate CPU sets:
114 CPU_ALLOC()
116 Allocate a CPU set large enough to hold CPUs in the range 0 to
117 num_cpus-1.
118 CPU_ALLOC_SIZE()
120 Return the size in bytes of the CPU set that would be needed to
121 hold CPUs in the range 0 to num_cpus-1. This macro provides the
122 value that can be used for the setsize argument in the CPU_*_S()
123 macros described below.
124 CPU_FREE()
126 Free a CPU set previously allocated by CPU_ALLOC().
127 The macros whose names end with "_S" are the analogs of the similarly
129 named macros without the suffix. These macros perform the same tasks
130 as their analogs, but operate on the dynamically allocated CPU set(s)
131 whose size is setsize bytes.
132
134 CPU_ISSET() and CPU_ISSET_S() return nonzero if cpu is in set; other‐
135 wise, it returns 0.
136 CPU_COUNT() and CPU_COUNT_S() return the number of CPUs in set.
138 CPU_EQUAL() and CPU_EQUAL_S() return nonzero if the two CPU sets are
140 equal; otherwise they return 0.
141 CPU_ALLOC() returns a pointer on success, or NULL on failure. (Errors
143 are as for malloc(3).)
144 CPU_ALLOC_SIZE() returns the number of bytes required to store a CPU
146 set of the specified cardinality.
147 The other functions do not return a value.
149
151 The CPU_ZERO(), CPU_SET(), CPU_CLR(), and CPU_ISSET() macros were added
152 in glibc 2.3.3.
153 CPU_COUNT() first appeared in glibc 2.6.
155 CPU_AND(), CPU_OR(), CPU_XOR(), CPU_EQUAL(), CPU_ALLOC(), CPU_AL‐
157 LOC_SIZE(), CPU_FREE(), CPU_ZERO_S(), CPU_SET_S(), CPU_CLR_S(), CPU_IS‐
158 SET_S(), CPU_AND_S(), CPU_OR_S(), CPU_XOR_S(), and CPU_EQUAL_S() first
159 appeared in glibc 2.7.
160
162 These interfaces are Linux-specific.
163
165 To duplicate a CPU set, use memcpy(3).
166 Since CPU sets are bit masks allocated in units of long words, the ac‐
168 tual number of CPUs in a dynamically allocated CPU set will be rounded
169 up to the next multiple of sizeof(unsigned long). An application
170 should consider the contents of these extra bits to be undefined.
171 Notwithstanding the similarity in the names, note that the constant
173 CPU_SETSIZE indicates the number of CPUs in the cpu_set_t data type
174 (thus, it is effectively a count of the bits in the bit mask), while
175 the setsize argument of the CPU_*_S() macros is a size in bytes.
176 The data types for arguments and return values shown in the SYNOPSIS
178 are hints what about is expected in each case. However, since these
179 interfaces are implemented as macros, the compiler won't necessarily
180 catch all type errors if you violate the suggestions.
181
183 On 32-bit platforms with glibc 2.8 and earlier, CPU_ALLOC() allocates
184 twice as much space as is required, and CPU_ALLOC_SIZE() returns a
185 value twice as large as it should. This bug should not affect the se‐
186 mantics of a program, but does result in wasted memory and less effi‐
187 cient operation of the macros that operate on dynamically allocated CPU
188 sets. These bugs are fixed in glibc 2.9.
189
191 The following program demonstrates the use of some of the macros used
192 for dynamically allocated CPU sets.
193 #define _GNU_SOURCE
195 #include <sched.h>
196 #include <stdlib.h>
197 #include <unistd.h>
198 #include <stdio.h>
199 #include <assert.h>
200 int
202 main(int argc, char *argv[])
203 {
204 cpu_set_t *cpusetp;
205 size_t size;
206 int num_cpus;
207 if (argc < 2) {
209 fprintf(stderr, "Usage: %s <num-cpus>\n", argv[0]);
210 exit(EXIT_FAILURE);
211 }
212 num_cpus = atoi(argv[1]);
214 cpusetp = CPU_ALLOC(num_cpus);
216 if (cpusetp == NULL) {
217 perror("CPU_ALLOC");
218 exit(EXIT_FAILURE);
219 }
220 size = CPU_ALLOC_SIZE(num_cpus);
222 CPU_ZERO_S(size, cpusetp);
224 for (int cpu = 0; cpu < num_cpus; cpu += 2)
225 CPU_SET_S(cpu, size, cpusetp);
226 printf("CPU_COUNT() of set: %d\n", CPU_COUNT_S(size, cpusetp));
228 CPU_FREE(cpusetp);
230 exit(EXIT_SUCCESS);
231 }
232
234 sched_setaffinity(2), pthread_attr_setaffinity_np(3), pthread_setaffin‐
235 ity_np(3), cpuset(7)
236
238 This page is part of release 5.10 of the Linux man-pages project. A
239 description of the project, information about reporting bugs, and the
240 latest version of this page, can be found at
241 https://www.kernel.org/doc/man-pages/.
242Linux 2020-11-01 CPU_SET(3)