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() Clears set, so that it contains no CPUs.
64 CPU_SET() Add CPU cpu to set.
66 CPU_CLR() Remove CPU cpu from set.
68 CPU_ISSET() Test to see if CPU cpu is a member of set.
70 CPU_COUNT() Return the number of CPUs in set.
72 Where a cpu argument is specified, it should not produce side effects,
74 since the above macros may evaluate the argument more than once.
75 The first CPU on the system corresponds to a cpu value of 0, the next
77 CPU corresponds to a cpu value of 1, and so on. No assumptions should
78 be made about particular CPUs being available, or the set of CPUs being
79 contiguous, since CPUs can be taken offline dynamically or be otherwise
80 absent. The constant CPU_SETSIZE (currently 1024) specifies a value
81 one greater than the maximum CPU number that can be stored in
82 cpu_set_t.
83 The following macros perform logical operations on CPU sets:
85 CPU_AND() Store the intersection of the sets srcset1 and srcset2
87 in destset (which may be one of the source sets).
88 CPU_OR() Store the union of the sets srcset1 and srcset2 in
90 destset (which may be one of the source sets).
91 CPU_XOR() Store the XOR of the sets srcset1 and srcset2 in dest‐
93 set (which may be one of the source sets). The XOR
94 means the set of CPUs that are in either srcset1 or
95 srcset2, but not both.
96 CPU_EQUAL() Test whether two CPU set contain exactly the same
98 CPUs.
99 Dynamically sized CPU sets
101 Because some applications may require the ability to dynamically size
102 CPU sets (e.g., to allocate sets larger than that defined by the stan‐
103 dard cpu_set_t data type), glibc nowadays provides a set of macros to
104 support this.
105 The following macros are used to allocate and deallocate CPU sets:
107 CPU_ALLOC() Allocate a CPU set large enough to hold CPUs in the
109 range 0 to num_cpus-1.
110 CPU_ALLOC_SIZE() Return the size in bytes of the CPU set that would be
112 needed to hold CPUs in the range 0 to num_cpus-1.
113 This macro provides the value that can be used for the
114 setsize argument in the CPU_*_S() macros described
115 below.
116 CPU_FREE() Free a CPU set previously allocated by CPU_ALLOC().
118 The macros whose names end with "_S" are the analogs of the similarly
120 named macros without the suffix. These macros perform the same tasks
121 as their analogs, but operate on the dynamically allocated CPU set(s)
122 whose size is setsize bytes.
123
125 CPU_ISSET() and CPU_ISSET_S() return nonzero if cpu is in set; other‐
126 wise, it returns 0.
127 CPU_COUNT() and CPU_COUNT_S() return the number of CPUs in set.
129 CPU_EQUAL() and CPU_EQUAL_S() return nonzero if the two CPU sets are
131 equal; otherwise they return 0.
132 CPU_ALLOC() returns a pointer on success, or NULL on failure. (Errors
134 are as for malloc(3).)
135 CPU_ALLOC_SIZE() returns the number of bytes required to store a CPU
137 set of the specified cardinality.
138 The other functions do not return a value.
140
142 The CPU_ZERO(), CPU_SET(), CPU_CLR(), and CPU_ISSET() macros were added
143 in glibc 2.3.3.
144 CPU_COUNT() first appeared in glibc 2.6.
146 CPU_AND(), CPU_OR(), CPU_XOR(), CPU_EQUAL(), CPU_ALLOC(),
148 CPU_ALLOC_SIZE(), CPU_FREE(), CPU_ZERO_S(), CPU_SET_S(), CPU_CLR_S(),
149 CPU_ISSET_S(), CPU_AND_S(), CPU_OR_S(), CPU_XOR_S(), and CPU_EQUAL_S()
150 first appeared in glibc 2.7.
151
153 These interfaces are Linux-specific.
154
156 To duplicate a CPU set, use memcpy(3).
157 Since CPU sets are bit masks allocated in units of long words, the
159 actual number of CPUs in a dynamically allocated CPU set will be
160 rounded up to the next multiple of sizeof(unsigned long). An applica‐
161 tion should consider the contents of these extra bits to be undefined.
162 Notwithstanding the similarity in the names, note that the constant
164 CPU_SETSIZE indicates the number of CPUs in the cpu_set_t data type
165 (thus, it is effectively a count of the bits in the bit mask), while
166 the setsize argument of the CPU_*_S() macros is a size in bytes.
167 The data types for arguments and return values shown in the SYNOPSIS
169 are hints what about is expected in each case. However, since these
170 interfaces are implemented as macros, the compiler won't necessarily
171 catch all type errors if you violate the suggestions.
172
174 On 32-bit platforms with glibc 2.8 and earlier, CPU_ALLOC() allocates
175 twice as much space as is required, and CPU_ALLOC_SIZE() returns a
176 value twice as large as it should. This bug should not affect the
177 semantics of a program, but does result in wasted memory and less effi‐
178 cient operation of the macros that operate on dynamically allocated CPU
179 sets. These bugs are fixed in glibc 2.9.
180
182 The following program demonstrates the use of some of the macros used
183 for dynamically allocated CPU sets.
184 #define _GNU_SOURCE
186 #include <sched.h>
187 #include <stdlib.h>
188 #include <unistd.h>
189 #include <stdio.h>
190 #include <assert.h>
191 int
193 main(int argc, char *argv[])
194 {
195 cpu_set_t *cpusetp;
196 size_t size;
197 int num_cpus, cpu;
198 if (argc < 2) {
200 fprintf(stderr, "Usage: %s <num-cpus>\n", argv[0]);
201 exit(EXIT_FAILURE);
202 }
203 num_cpus = atoi(argv[1]);
205 cpusetp = CPU_ALLOC(num_cpus);
207 if (cpusetp == NULL) {
208 perror("CPU_ALLOC");
209 exit(EXIT_FAILURE);
210 }
211 size = CPU_ALLOC_SIZE(num_cpus);
213 CPU_ZERO_S(size, cpusetp);
215 for (cpu = 0; cpu < num_cpus; cpu += 2)
216 CPU_SET_S(cpu, size, cpusetp);
217 printf("CPU_COUNT() of set: %d\n", CPU_COUNT_S(size, cpusetp));
219 CPU_FREE(cpusetp);
221 exit(EXIT_SUCCESS);
222 }
223
225 sched_setaffinity(2), pthread_attr_setaffinity_np(3), pthread_setaffin‐
226 ity_np(3), cpuset(7)
227
229 This page is part of release 5.02 of the Linux man-pages project. A
230 description of the project, information about reporting bugs, and the
231 latest version of this page, can be found at
232 https://www.kernel.org/doc/man-pages/.
233Linux 2019-03-06 CPU_SET(3)