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
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 bitset. However, the data
58 structure treated as considered opaque: all manipulation of CPU sets
59 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 available CPU on the system corresponds to a cpu value of 0,
77 the next CPU corresponds to a cpu value of 1, and so on. The constant
78 CPU_SETSIZE (currently 1024) specifies a value one greater than the
79 maximum CPU number that can be stored in cpu_set_t.
80 The following macros perform logical operations on CPU sets:
82 CPU_AND() Store the logical AND of the sets srcset1 and srcset2
84 in destset (which may be one of the source sets).
85 CPU_OR() Store the logical OR of the sets srcset1 and srcset2
87 in destset (which may be one of the source sets).
88 CPU_XOR() Store the logical XOR of the sets srcset1 and srcset2
90 in destset (which may be one of the source sets).
91 CPU_EQUAL() Test whether two CPU set contain exactly the same
93 CPUs.
94 Dynamically sized CPU sets
96 Because some applications may require the ability to dynamically size
97 CPU sets (e.g., to allocate sets larger than that defined by the stan‐
98 dard cpu_set_t data type), glibc nowadays provides a set of macros to
99 support this.
100 The following macros are used to allocate and deallocate CPU sets:
102 CPU_ALLOC() Allocate a CPU set large enough to hold CPUs in the
104 range 0 to num_cpus-1.
105 CPU_ALLOC_SIZE() Return the size in bytes of the CPU set that would be
107 needed to hold CPUs in the range 0 to num_cpus-1.
108 This macro provides the value that can be used for the
109 setsize argument in the CPU_*_S() macros described
110 below.
111 CPU_FREE() Free a CPU set previously allocated by CPU_ALLOC().
113 The macros whose names end with "_S" are the analogs of the similarly
115 named macros without the suffix. These macros perform the same tasks
116 as their analogs, but operate on the dynamically allocated CPU set(s)
117 whose size is setsize bytes.
118
120 CPU_ISSET() and CPU_ISSET_S() return nonzero if cpu is in set; other‐
121 wise, it returns 0.
122 CPU_COUNT() and CPU_COUNT_S() return the number of CPUs in set.
124 CPU_EQUAL() and CPU_EQUAL_S() return nonzero if the two CPU sets are
126 equal; otherwise it returns 0.
127 CPU_ALLOC() returns a pointer on success, or NULL on failure. (Errors
129 are as for malloc(3).)
130 CPU_ALLOC_SIZE() returns the number of bytes required to store a CPU
132 set of the specified cardinality.
133 The other functions do not return a value.
135
137 The CPU_ZERO(), CPU_SET(), CPU_CLR(), and CPU_ISSET() macros were added
138 in glibc 2.3.3.
139 CPU_COUNT() first appeared in glibc 2.6.
141 CPU_AND(), CPU_OR(), CPU_XOR(), CPU_EQUAL(), CPU_ALLOC(),
143 CPU_ALLOC_SIZE(), CPU_FREE(), CPU_ZERO_S(), CPU_SET_S(), CPU_CLR_S(),
144 CPU_ISSET_S(), CPU_AND_S(), CPU_OR_S(), CPU_XOR_S(), and CPU_EQUAL_S()
145 first appeared in glibc 2.7.
146
148 These interfaces are Linux-specific.
149
151 To duplicate a CPU set, use memcpy(3).
152 Since CPU sets are bitsets allocated in units of long words, the actual
154 number of CPUs in a dynamically allocated CPU set will be rounded up to
155 the next multiple of sizeof(unsigned long). An application should con‐
156 sider the contents of these extra bits to be undefined.
157 Notwithstanding the similarity in the names, note that the constant
159 CPU_SETSIZE indicates the number of CPUs in the cpu_set_t data type
160 (thus, it is effectively a count of bits in the bitset), while the set‐
161 size argument of the CPU_*_S() macros is a size in bytes.
162 The data types for arguments and return values shown in the SYNOPSIS
164 are hints what about is expected in each case. However, since these
165 interfaces are implemented as macros, the compiler won't necessarily
166 catch all type errors if you violate the suggestions.
167
169 The following program demonstrates the use of some of the macros used
170 for dynamically allocated CPU sets.
171 #define _GNU_SOURCE
173 #include <sched.h>
174 #include <stdlib.h>
175 #include <unistd.h>
176 #include <stdio.h>
177 #include <assert.h>
178 int
180 main(int argc, char *argv[])
181 {
182 cpu_set_t *cpusetp;
183 size_t size;
184 int num_cpus, cpu;
185 if (argc < 2) {
187 fprintf(stderr, "Usage: %s <num-cpus>\n", argv[0]);
188 exit(EXIT_FAILURE);
189 }
190 num_cpus = atoi(argv[1]);
192 cpusetp = CPU_ALLOC(num_cpus);
194 if (cpusetp == NULL) {
195 perror("CPU_ALLOC");
196 exit(EXIT_FAILURE);
197 }
198 size = CPU_ALLOC_SIZE(num_cpus);
200 CPU_ZERO_S(size, cpusetp);
202 for (cpu = 0; cpu < num_cpus; cpu += 2)
203 CPU_SET_S(cpu, size, cpusetp);
204 printf("CPU_COUNT() of set: %d\n", CPU_COUNT_S(size, cpusetp));
206 CPU_FREE(cpusetp);
208 exit(EXIT_SUCCESS);
209 }
210
212 On 32-bit platforms with glibc 2.8 and earlier, CPU_ALLOC() allocates
213 twice as much space as is required, and CPU_ALLOC_SIZE() returns a
214 value twice as large as it should. This bug should not affect the
215 semantics of a program, but does result in wasted memory and less effi‐
216 cient operation of the macros that operate on dynamically allocated CPU
217 sets. These bugs are fixed in glibc 2.9.
218
220 sched_setaffinity(2), pthread_attr_setaffinity_np(3), pthread_setaffin‐
221 ity_np(3), cpuset(7)
222
224 This page is part of release 3.25 of the Linux man-pages project. A
225 description of the project, and information about reporting bugs, can
226 be found at http://www.kernel.org/doc/man-pages/.
227Linux 2010-02-21 CPU_SET(3)