tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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}