[PATCH v4 2/3] perf tsc: Add cpuinfo fall back for arch_get_tsc_freq

From: Ian Rogers
Date: Mon Jul 18 2022 - 12:43:32 EST


The CPUID method of arch_get_tsc_freq fails for older Intel processors,
such as Skylake. Compute using /proc/cpuinfo.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
tools/perf/arch/x86/util/tsc.c | 52 +++++++++++++++++++++++++++++++---
1 file changed, 48 insertions(+), 4 deletions(-)

diff --git a/tools/perf/arch/x86/util/tsc.c b/tools/perf/arch/x86/util/tsc.c
index b69144f22489..eb2b5195bd02 100644
--- a/tools/perf/arch/x86/util/tsc.c
+++ b/tools/perf/arch/x86/util/tsc.c
@@ -1,7 +1,9 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/types.h>
+#include <math.h>
#include <string.h>

+#include "../../../util/debug.h"
#include "../../../util/tsc.h"
#include "cpuid.h"

@@ -14,6 +16,44 @@ u64 rdtsc(void)
return low | ((u64)high) << 32;
}

+/*
+ * Derive the TSC frequency in Hz from the /proc/cpuinfo, for example:
+ * ...
+ * model name : Intel(R) Xeon(R) Gold 6154 CPU @ 3.00GHz
+ * ...
+ * will return 3000000000.
+ */
+static double cpuinfo_tsc_freq(void)
+{
+ double result = 0;
+ FILE *cpuinfo;
+ char *line = NULL;
+ size_t len = 0;
+
+ cpuinfo = fopen("/proc/cpuinfo", "r");
+ if (!cpuinfo) {
+ pr_err("Failed to read /proc/cpuinfo for TSC frequency");
+ return NAN;
+ }
+ while (getline(&line, &len, cpuinfo) > 0) {
+ if (!strncmp(line, "model name", 10)) {
+ char *pos = strstr(line + 11, " @ ");
+
+ if (pos && sscanf(pos, " @ %lfGHz", &result) == 1) {
+ result *= 1000000000;
+ goto out;
+ }
+ }
+ }
+out:
+ if (fpclassify(result) == FP_ZERO)
+ pr_err("Failed to find TSC frequency in /proc/cpuinfo");
+
+ free(line);
+ fclose(cpuinfo);
+ return result;
+}
+
double arch_get_tsc_freq(void)
{
unsigned int a, b, c, d, lvl;
@@ -33,13 +73,17 @@ double arch_get_tsc_freq(void)
* Don't support Time Stamp Counter and
* Nominal Core Crystal Clock Information Leaf.
*/
- if (lvl < 0x15)
- return 0;
+ if (lvl < 0x15) {
+ tsc = cpuinfo_tsc_freq();
+ return tsc;
+ }

cpuid(0x15, 0, &a, &b, &c, &d);
/* TSC frequency is not enumerated */
- if (!a || !b || !c)
- return 0;
+ if (!a || !b || !c) {
+ tsc = cpuinfo_tsc_freq();
+ return tsc;
+ }

tsc = (double)c * (double)b / (double)a;
return tsc;
--
2.37.0.170.g444d1eabd0-goog