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CPU_SET(3) Linux Programmer's Manual CPU_SET(3)
CPU_SET, CPU_CLR, CPU_ISSET, CPU_ZERO, CPU_COUNT, CPU_AND, CPU_OR, CPU_XOR,
CPU_EQUAL, CPU_ALLOC, CPU_ALLOC_SIZE, CPU_FREE, CPU_SET_S, CPU_CLR_S,
CPU_ISSET_S, CPU_ZERO_S, CPU_COUNT_S, CPU_AND_S, CPU_OR_S, CPU_XOR_S,
CPU_EQUAL_S - macros for manipulating CPU sets
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <sched.h>
void CPU_ZERO(cpu_set_t *set);
void CPU_SET(int cpu, cpu_set_t *set);
void CPU_CLR(int cpu, cpu_set_t *set);
int CPU_ISSET(int cpu, cpu_set_t *set);
int CPU_COUNT(cpu_set_t *set);
void CPU_AND(cpu_set_t *destset,
cpu_set_t *srcset1, cpu_set_t *srcset2);
void CPU_OR(cpu_set_t *destset,
cpu_set_t *srcset1, cpu_set_t *srcset2);
void CPU_XOR(cpu_set_t *destset,
cpu_set_t *srcset1, cpu_set_t *srcset2);
int CPU_EQUAL(cpu_set_t *set1, cpu_set_t *set2);
cpu_set_t *CPU_ALLOC(int num_cpus);
void CPU_FREE(cpu_set_t *set);
size_t CPU_ALLOC_SIZE(int num_cpus);
void CPU_ZERO_S(size_t setsize, cpu_set_t *set);
void CPU_SET_S(int cpu, size_t setsize, cpu_set_t *set);
void CPU_CLR_S(int cpu, size_t setsize, cpu_set_t *set);
int CPU_ISSET_S(int cpu, size_t setsize, cpu_set_t *set);
int CPU_COUNT_S(size_t setsize, cpu_set_t *set);
void CPU_AND_S(size_t setsize, cpu_set_t *destset,
cpu_set_t *srcset1, cpu_set_t *srcset2);
void CPU_OR_S(size_t setsize, cpu_set_t *destset,
cpu_set_t *srcset1, cpu_set_t *srcset2);
void CPU_XOR_S(size_t setsize, cpu_set_t *destset,
cpu_set_t *srcset1, cpu_set_t *srcset2);
int CPU_EQUAL_S(size_t setsize, cpu_set_t *set1, cpu_set_t *set2);
The cpu_set_t data structure represents a set of CPUs. CPU sets are used by
sched_setaffinity(2) and similar interfaces.
The cpu_set_t data type is implemented as a bitset. However, the data
structure treated as considered opaque: all manipulation of CPU sets should be
done via the macros described in this page.
The following macros are provided to operate on the CPU set set:
CPU_ZERO() Clears set, so that it contains no CPUs.
CPU_SET() Add CPU cpu to set.
CPU_CLR() Remove CPU cpu from set.
CPU_ISSET() Test to see if CPU cpu is a member of set.
CPU_COUNT() Return the number of CPUs in set.
Where a cpu argument is specified, it should not produce side effects, since
the above macros may evaluate the argument more than once.
The first available CPU on the system corresponds to a cpu value of 0, the
next CPU corresponds to a cpu value of 1, and so on. The constant CPU_SETSIZE
(currently 1024) specifies a value one greater than the maximum CPU number
that can be stored in cpu_set_t.
The following macros perform logical operations on CPU sets:
CPU_AND() Store the intersection of the sets srcset1 and srcset2 in
destset (which may be one of the source sets).
CPU_OR() Store the union of the sets srcset1 and srcset2 in destset
(which may be one of the source sets).
CPU_XOR() Store the XOR of the sets srcset1 and srcset2 in destset
(which may be one of the source sets). The XOR means the set
of CPUs that are in either srcset1 or srcset2, but not both.
CPU_EQUAL() Test whether two CPU set contain exactly the same CPUs.
Because some applications may require the ability to dynamically size CPU sets
(e.g., to allocate sets larger than that defined by the standard cpu_set_t
data type), glibc nowadays provides a set of macros to support this.
The following macros are used to allocate and deallocate CPU sets:
CPU_ALLOC() Allocate a CPU set large enough to hold CPUs in the range 0
to num_cpus-1.
CPU_ALLOC_SIZE() Return the size in bytes of the CPU set that would be needed
to hold CPUs in the range 0 to num_cpus-1. This macro
provides the value that can be used for the setsize argument
in the CPU_*_S() macros described below.
CPU_FREE() Free a CPU set previously allocated by CPU_ALLOC().
The macros whose names end with "_S" are the analogs of the similarly named
macros without the suffix. These macros perform the same tasks as their
analogs, but operate on the dynamically allocated CPU set(s) whose size is
setsize bytes.
CPU_ISSET() and CPU_ISSET_S() return nonzero if cpu is in set; otherwise, it
returns 0.
CPU_COUNT() and CPU_COUNT_S() return the number of CPUs in set.
CPU_EQUAL() and CPU_EQUAL_S() return nonzero if the two CPU sets are equal;
otherwise it returns 0.
CPU_ALLOC() returns a pointer on success, or NULL on failure. (Errors are as
for malloc(3).)
CPU_ALLOC_SIZE() returns the number of bytes required to store a CPU set of
the specified cardinality.
The other functions do not return a value.
The CPU_ZERO(), CPU_SET(), CPU_CLR(), and CPU_ISSET() macros were added in
glibc 2.3.3.
CPU_COUNT() first appeared in glibc 2.6.
CPU_AND(), CPU_OR(), CPU_XOR(), CPU_EQUAL(), CPU_ALLOC(), CPU_ALLOC_SIZE(),
CPU_FREE(), CPU_ZERO_S(), CPU_SET_S(), CPU_CLR_S(), CPU_ISSET_S(),
CPU_AND_S(), CPU_OR_S(), CPU_XOR_S(), and CPU_EQUAL_S() first appeared in
glibc 2.7.
These interfaces are Linux-specific.
To duplicate a CPU set, use memcpy(3).
Since CPU sets are bitsets allocated in units of long words, the actual number
of CPUs in a dynamically allocated CPU set will be rounded up to the next
multiple of sizeof(unsigned long). An application should consider the
contents of these extra bits to be undefined.
Notwithstanding the similarity in the names, note that the constant
CPU_SETSIZE indicates the number of CPUs in the cpu_set_t data type (thus, it
is effectively a count of bits in the bitset), while the setsize argument of
the CPU_*_S() macros is a size in bytes.
The data types for arguments and return values shown in the SYNOPSIS are hints
what about is expected in each case. However, since these interfaces are
implemented as macros, the compiler won't necessarily catch all type errors if
you violate the suggestions.
The following program demonstrates the use of some of the macros used for
dynamically allocated CPU sets.
#define _GNU_SOURCE
#include <sched.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <assert.h>
int
main(int argc, char *argv[])
{
cpu_set_t *cpusetp;
size_t size;
int num_cpus, cpu;
if (argc < 2) {
fprintf(stderr, "Usage: %s <num-cpus>\n", argv[0]);
exit(EXIT_FAILURE);
}
num_cpus = atoi(argv[1]);
cpusetp = CPU_ALLOC(num_cpus);
if (cpusetp == NULL) {
perror("CPU_ALLOC");
exit(EXIT_FAILURE);
}
size = CPU_ALLOC_SIZE(num_cpus);
CPU_ZERO_S(size, cpusetp);
for (cpu = 0; cpu < num_cpus; cpu += 2)
CPU_SET_S(cpu, size, cpusetp);
printf("CPU_COUNT() of set: %d\n", CPU_COUNT_S(size, cpusetp));
CPU_FREE(cpusetp);
exit(EXIT_SUCCESS);
}
On 32-bit platforms with glibc 2.8 and earlier, CPU_ALLOC() allocates twice as
much space as is required, and CPU_ALLOC_SIZE() returns a value twice as large
as it should. This bug should not affect the semantics of a program, but does
result in wasted memory and less efficient operation of the macros that
operate on dynamically allocated CPU sets. These bugs are fixed in glibc 2.9.
sched_setaffinity(2), pthread_attr_setaffinity_np(3),
pthread_setaffinity_np(3), cpuset(7)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2010-09-10 CPU_SET(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface