pthread_setaffinity_np, pthread_getaffinity_np - set/get CPU affinity of a thread

#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <pthread.h>
int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize,
 const cpu_set_t *cpuset);
int pthread_getaffinity_np(pthread_t thread, size_t cpusetsize,
 cpu_set_t *cpuset);

The pthread_setaffinity_np() function sets the CPU affinity mask of the thread thread to the CPU set pointed to by cpuset. If the call is successful, and the thread is not currently running on one of the CPUs in cpuset, then it is migrated to one of those CPUs.

The pthread_getaffinity_np() function returns the CPU affinity mask of the thread thread in the buffer pointed to by cpuset.

For more details on CPU affinity masks, see sched_setaffinity(2). For a description of a set of macros that can be used to manipulate and inspect CPU sets, see CPU_SET(3).

The argument cpusetsize is the length (in bytes) of the buffer pointed to by cpuset. Typically, this argument would be specified as sizeof(cpu_set_t). (It may be some other value, if using the macros described in CPU_SET(3) for dynamically allocating a CPU set.)

On success, these functions return 0; on error, they return a nonzero error number.

In the following program, the main thread uses pthread_setaffinity_np() to set its CPU affinity mask to include CPUs 0 to 7 (which may not all be available on the system), and then calls pthread_getaffinity_np() to check the resulting CPU affinity mask of the thread.

#define _GNU_SOURCE
#include <err.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
    int s;
    cpu_set_t cpuset;
    pthread_t thread;
    thread = pthread_self();
    /* Set affinity mask to include CPUs 0 to 7. */
    CPU_ZERO(&cpuset);
    for (size_t j = 0; j < 8; j++)
        CPU_SET(j, &cpuset);
    s = pthread_setaffinity_np(thread, sizeof(cpuset), &cpuset);
    if (s != 0)
        errc(EXIT_FAILURE, s, "pthread_setaffinity_np");
    /* Check the actual affinity mask assigned to the thread. */
    s = pthread_getaffinity_np(thread, sizeof(cpuset), &cpuset);
    if (s != 0)
        errc(EXIT_FAILURE, s, "pthread_getaffinity_np");
    printf("Set returned by pthread_getaffinity_np() contained:\n");
    for (size_t j = 0; j < CPU_SETSIZE; j++)
        if (CPU_ISSET(j, &cpuset))
            printf("    CPU %zu\n", j);
    exit(EXIT_SUCCESS);
}

sched_setaffinity(2), CPU_SET(3), pthread_attr_setaffinity_np(3), pthread_self(3), sched_getcpu(3), cpuset(7), pthreads(7), sched(7)