tools/perf/util/smt.c

   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
   8 int 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         if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) > 0)
  19                 goto done;
  20
  21         ncpu = sysconf(_SC_NPROCESSORS_CONF);
  22         for (cpu = 0; cpu < ncpu; cpu++) {
  23                 unsigned long long siblings;
  24                 char *str;
  25                 size_t strlen;
  26                 char fn[256];
  27
  28                 snprintf(fn, sizeof fn,
  29                         "devices/system/cpu/cpu%d/topology/core_cpus", cpu);
  30                 if (sysfs__read_str(fn, &str, &strlen) < 0) {
  31                         snprintf(fn, sizeof fn,
  32                                 "devices/system/cpu/cpu%d/topology/thread_siblings",
  33                                 cpu);
  34                         if (sysfs__read_str(fn, &str, &strlen) < 0)
  35                                 continue;
  36                 }
  37                 /* Entry is hex, but does not have 0x, so need custom parser */
  38                 siblings = strtoull(str, NULL, 16);
  39                 free(str);
  40                 if (hweight64(siblings) > 1) {
  41                         cached_result = 1;
  42                         cached = true;
  43                         break;
  44                 }
  45         }
  46         if (!cached) {
  47                 cached_result = 0;
  48 done:
  49                 cached = true;
  50         }
  51         return cached_result;
  52 }