tools/perf/arch/x86/util/tsc.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/types.h>
   3 #include <math.h>
   4 #include <string.h>
   5 #include <stdlib.h>
   6
   7 #include "../../../util/debug.h"
   8 #include "../../../util/tsc.h"
   9 #include "cpuid.h"
  10
  11 u64 rdtsc(void)
  12 {
  13         unsigned int low, high;
  14
  15         asm volatile("rdtsc" : "=a" (low), "=d" (high));
  16
  17         return low | ((u64)high) << 32;
  18 }
  19
  20 /*
  21  * Derive the TSC frequency in Hz from the /proc/cpuinfo, for example:
  22  * ...
  23  * model name      : Intel(R) Xeon(R) Gold 6154 CPU @ 3.00GHz
  24  * ...
  25  * will return 3000000000.
  26  */
  27 static u64 cpuinfo_tsc_freq(void)
  28 {
  29         u64 result = 0;
  30         FILE *cpuinfo;
  31         char *line = NULL;
  32         size_t len = 0;
  33
  34         cpuinfo = fopen("/proc/cpuinfo", "r");
  35         if (!cpuinfo) {
  36                 pr_err("Failed to read /proc/cpuinfo for TSC frequency\n");
  37                 return 0;
  38         }
  39         while (getline(&line, &len, cpuinfo) > 0) {
  40                 if (!strncmp(line, "model name", 10)) {
  41                         char *pos = strstr(line + 11, " @ ");
  42                         double float_result;
  43
  44                         if (pos && sscanf(pos, " @ %lfGHz", &float_result) == 1) {
  45                                 float_result *= 1000000000;
  46                                 result = (u64)float_result;
  47                                 goto out;
  48                         }
  49                 }
  50         }
  51 out:
  52         if (result == 0)
  53                 pr_err("Failed to find TSC frequency in /proc/cpuinfo\n");
  54
  55         free(line);
  56         fclose(cpuinfo);
  57         return result;
  58 }
  59
  60 u64 arch_get_tsc_freq(void)
  61 {
  62         unsigned int a, b, c, d, lvl;
  63         static bool cached;
  64         static double tsc;
  65         char vendor[16];
  66
  67         if (cached)
  68                 return tsc;
  69
  70         cached = true;
  71         get_cpuid_0(vendor, &lvl);
  72         if (!strstr(vendor, "Intel"))
  73                 return 0;
  74
  75         /*
  76          * Don't support Time Stamp Counter and
  77          * Nominal Core Crystal Clock Information Leaf.
  78          */
  79         if (lvl < 0x15) {
  80                 tsc = cpuinfo_tsc_freq();
  81                 return tsc;
  82         }
  83
  84         cpuid(0x15, 0, &a, &b, &c, &d);
  85         /* TSC frequency is not enumerated */
  86         if (!a || !b || !c) {
  87                 tsc = cpuinfo_tsc_freq();
  88                 return tsc;
  89         }
  90
  91         tsc = (u64)c * (u64)b / (u64)a;
  92         return tsc;
  93 }