smt.c

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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/bitops.h>
#include "api/fs/fs.h"
#include "smt.h"

int smt_on(void)
{
    static bool cached;
    static int cached_result;
    int cpu;
    int ncpu;

    if (cached)
        return cached_result;

    ncpu = sysconf(_SC_NPROCESSORS_CONF);
    for (cpu = 0; cpu < ncpu; cpu++) {
        unsigned long long siblings;
        char *str;
        size_t strlen;
        char fn[256];

        snprintf(fn, sizeof fn,
            "devices/system/cpu/cpu%d/topology/thread_siblings",
            cpu);
        if (sysfs__read_str(fn, &str, &strlen) < 0)
            continue;
        /* Entry is hex, but does not have 0x, so need custom parser */
        siblings = strtoull(str, NULL, 16);
        free(str);
        if (hweight64(siblings) > 1) {
            cached_result = 1;
            cached = true;
            break;
        }
    }
    if (!cached) {
        cached_result = 0;
        cached = true;
    }
    return cached_result;
}