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