CPU_SET



CPU_SET

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
VERSIONS
CONFORMING TO
NOTES
BUGS
EXAMPLE
SEE ALSO
COLOPHON

NAME

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

SYNOPSIS

#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);

DESCRIPTION

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 bit set. 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.

Dynamically sized CPU sets
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.

RETURN VALUE

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.

VERSIONS

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.

CONFORMING TO

These interfaces are Linux-specific.

NOTES

To duplicate a CPU set, use memcpy(3).

Since CPU sets are bit sets 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 bit set), 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.

BUGS

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.

EXAMPLE

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);
}

SEE ALSO

sched_setaffinity(2), pthread_attr_setaffinity_np(3), pthread_setaffinity_np(3), cpuset(7)

COLOPHON

This page is part of release 3.69 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man−pages/.







Opportunity


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.





Free Software


Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.


Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.





Free Books


The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.


Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.





Education


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.


Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.