perf/util/smt.c

0001 #include <stdio.h>
0002 #include <stdlib.h>
0003 #include <unistd.h>
0004 #include <linux/bitops.h>
0005 #include "api/fs/fs.h"
0006 #include "smt.h"
0007
0008 /**
0009  * hweight_str - Returns the number of bits set in str. Stops at first non-hex
0010  *         or ',' character.
0011  */
0012 static int hweight_str(char *str)
0013 {
0014     int result = 0;
0015
0016     while (*str) {
0017         switch (*str++) {
0018         case '0':
0019         case ',':
0020             break;
0021         case '1':
0022         case '2':
0023         case '4':
0024         case '8':
0025             result++;
0026             break;
0027         case '3':
0028         case '5':
0029         case '6':
0030         case '9':
0031         case 'a':
0032         case 'A':
0033         case 'c':
0034         case 'C':
0035             result += 2;
0036             break;
0037         case '7':
0038         case 'b':
0039         case 'B':
0040         case 'd':
0041         case 'D':
0042         case 'e':
0043         case 'E':
0044             result += 3;
0045             break;
0046         case 'f':
0047         case 'F':
0048             result += 4;
0049             break;
0050         default:
0051             goto done;
0052         }
0053     }
0054 done:
0055     return result;
0056 }
0057
0058 int smt_on(void)
0059 {
0060     static bool cached;
0061     static int cached_result;
0062     int cpu;
0063     int ncpu;
0064
0065     if (cached)
0066         return cached_result;
0067
0068     if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0) {
0069         cached = true;
0070         return cached_result;
0071     }
0072
0073     cached_result = 0;
0074     ncpu = sysconf(_SC_NPROCESSORS_CONF);
0075     for (cpu = 0; cpu < ncpu; cpu++) {
0076         unsigned long long siblings;
0077         char *str;
0078         size_t strlen;
0079         char fn[256];
0080
0081         snprintf(fn, sizeof fn,
0082             "devices/system/cpu/cpu%d/topology/thread_siblings", cpu);
0083         if (sysfs__read_str(fn, &str, &strlen) < 0) {
0084             snprintf(fn, sizeof fn,
0085                 "devices/system/cpu/cpu%d/topology/core_cpus", cpu);
0086             if (sysfs__read_str(fn, &str, &strlen) < 0)
0087                 continue;
0088         }
0089         /* Entry is hex, but does not have 0x, so need custom parser */
0090         siblings = hweight_str(str);
0091         free(str);
0092         if (siblings > 1) {
0093             cached_result = 1;
0094             break;
0095         }
0096     }
0097     cached = true;
0098     return cached_result;
0099 }