set CPU affinity

1. config

worker_cpu_affinity: http://nginx.org/en/docs/ngx_core_module.html#worker_cpu_affinity, set cpumask.

/* Parse config worker_cpu_affinity */

extern ngx_int_t    ngx_ncpu;
ngx_ncpu = sysconf(_SC_NPROCESSORS_ONLN); // Get the number of processors currently online (available).


static char *
ngx_set_cpu_affinity(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
#if (NGX_HAVE_CPU_AFFINITY)
    ngx_core_conf_t  *ccf = conf;

    u_char            ch, *p;
    ngx_str_t        *value;
    ngx_uint_t        i, n;
    ngx_cpuset_t     *mask;

    if (ccf->cpu_affinity) {
        return "is duplicate";
    }

    mask = ngx_palloc(cf->pool, (cf->args->nelts - 1) * sizeof(ngx_cpuset_t));
    if (mask == NULL) {
        return NGX_CONF_ERROR;
    }

    ccf->cpu_affinity_n = cf->args->nelts - 1;
    ccf->cpu_affinity = mask;

    value = cf->args->elts;

    if (ngx_strcmp(value[1].data, "auto") == 0) {

        if (cf->args->nelts > 3) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid number of arguments in "
                               "\"worker_cpu_affinity\" directive");
            return NGX_CONF_ERROR;
        }

        ccf->cpu_affinity_auto = 1;

        CPU_ZERO(&mask[0]);
        for (i = 0; i < (ngx_uint_t) ngx_min(ngx_ncpu, CPU_SETSIZE); i++) {
            CPU_SET(i, &mask[0]);
        }

        n = 2;

    } else {
        n = 1;
    }

    for ( /* void */ ; n < cf->args->nelts; n++) {

        if (value[n].len > CPU_SETSIZE) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                         "\"worker_cpu_affinity\" supports up to %d CPUs only",
                         CPU_SETSIZE);
            return NGX_CONF_ERROR;
        }

        i = 0;
        CPU_ZERO(&mask[n - 1]);

        for (p = value[n].data + value[n].len - 1;
             p >= value[n].data;
             p--)
        {
            ch = *p;

            if (ch == ' ') {
                continue;
            }

            i++;

            if (ch == '0') {
                continue;
            }

            if (ch == '1') {
                CPU_SET(i - 1, &mask[n - 1]);
                continue;
            }

            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                          "invalid character \"%c\" in \"worker_cpu_affinity\"",
                          ch);
            return NGX_CONF_ERROR;
        }
    }

#else

    ngx_conf_log_error(NGX_LOG_WARN, cf, 0,
                       "\"worker_cpu_affinity\" is not supported "
                       "on this platform, ignored");
#endif

    return NGX_CONF_OK;
}

2. implemnet

typedef cpu_set_t  ngx_cpuset_t;

/* n is the sub process id, set from 0.
 */
ngx_cpuset_t *
ngx_get_cpu_affinity(ngx_uint_t n)
{
#if (NGX_HAVE_CPU_AFFINITY)
    ngx_uint_t        i, j;
    ngx_cpuset_t     *mask;
    ngx_core_conf_t  *ccf;

    static ngx_cpuset_t  result;

    ccf = (ngx_core_conf_t *) ngx_get_conf(ngx_cycle->conf_ctx,
                                           ngx_core_module);

    if (ccf->cpu_affinity == NULL) {
        return NULL;
    }

    if (ccf->cpu_affinity_auto) {
        mask = &ccf->cpu_affinity[ccf->cpu_affinity_n - 1];

        for (i = 0, j = n; /* void */ ; i++) {

            if (CPU_ISSET(i % CPU_SETSIZE, mask) && j-- == 0) { // If config mask is to set, then to set.
                break;
            }

            if (i == CPU_SETSIZE && j == n) {
                /* empty mask */
                return NULL;
            }

            /* void */
        }

        CPU_ZERO(&result);
        CPU_SET(i % CPU_SETSIZE, &result);

        return &result;
    }

    if (ccf->cpu_affinity_n > n) {
        return &ccf->cpu_affinity[n];
    }

    return &ccf->cpu_affinity[ccf->cpu_affinity_n - 1];

#else

    return NULL;

#endif
}


void
ngx_setaffinity(ngx_cpuset_t *cpu_affinity, ngx_log_t *log)
{
    ngx_uint_t  i;

    for (i = 0; i < CPU_SETSIZE; i++) {
        if (CPU_ISSET(i, cpu_affinity)) {
            ngx_log_error(NGX_LOG_NOTICE, log, 0,
                          "sched_setaffinity(): using cpu #%ui", i);
        }
    }

    if (sched_setaffinity(0, sizeof(cpu_set_t), cpu_affinity) == -1) {
        ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,
                      "sched_setaffinity() failed");
    }
}

Reference:

1. sysconf, _SC_NPROCESSORS_ONLN.
2. sched_setaffinity, sched_getaffinity.
3. CPU_SETSIZE, CPU_ISSET, CPU_ZERO, CPU_SET.