1#include <stdio.h>
 2#include <stdlib.h>
 3#include <unistd.h>
 4#include <linux/bitops.h>
 5#include "api/fs/fs.h"
 6#include "smt.h"
 7
 8int smt_on(void)
 9{
10	static bool cached;
11	static int cached_result;
12	int cpu;
13	int ncpu;
14
15	if (cached)
16		return cached_result;
17
18	ncpu = sysconf(_SC_NPROCESSORS_CONF);
19	for (cpu = 0; cpu < ncpu; cpu++) {
20		unsigned long long siblings;
21		char *str;
22		size_t strlen;
23		char fn[256];
24
25		snprintf(fn, sizeof fn,
26			"devices/system/cpu/cpu%d/topology/thread_siblings",
27			cpu);
28		if (sysfs__read_str(fn, &str, &strlen) < 0)
29			continue;
30		/* Entry is hex, but does not have 0x, so need custom parser */
31		siblings = strtoull(str, NULL, 16);
32		free(str);
33		if (hweight64(siblings) > 1) {
34			cached_result = 1;
35			cached = true;
36			break;
37		}
38	}
39	if (!cached) {
40		cached_result = 0;
41		cached = true;
42	}
43	return cached_result;
44}