[PATCH] perf metrics: Add literal for system TSC frequency

[Ian Rogers]

Such a literal is useful to calculate things like the average frequency
[1]. The TSC frequency isn't exposed by sysfs although some experimental
drivers look to add it [2]. This change computes the value using the
frequency in /proc/cpuinfo which is accruate at least on Intel
processors.

[1] https://github.com/intel/perfmon-metrics/blob/5ad9ef7056f31075e8178b9f1fb732af183b2c8d/SKX/metrics/perf/skx_metric_perf.json#L11
[2] https://github.com/trailofbits/tsc_freq_khz

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/expr.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
index 675f318ce7c1..7ad01ed57025 100644
--- a/tools/perf/util/expr.c
+++ b/tools/perf/util/expr.c
@@ -402,6 +402,43 @@ double expr_id_data__source_count(const struct expr_id_data *data)
 	return data->val.source_count;
 }
 
+/*
+ * 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 system_tsc_freq(void)
+{
+	double result = NAN;
+	FILE *cpuinfo;
+	char *line = NULL;
+	size_t len = 0;
+
+	cpuinfo = fopen("/proc/cpuinfo", "r");
+	if (!cpuinfo)
+		return NAN;
+
+	while (getline(&line, &len, cpuinfo) > 0) {
+		if (!strncmp(line, "model name", 10)) {
+			char *pos = line + 11;
+
+			while (*pos != '@')
+				pos++;
+			if (sscanf(pos, " %lfGHz", &result) == 1) {
+				result *= 1000000000;
+				goto out;
+			}
+		}
+	}
+
+out:
+	free(line);
+	fclose(cpuinfo);
+	return result;
+}
+
 double expr__get_literal(const char *literal)
 {
 	static struct cpu_topology *topology;
@@ -417,6 +454,11 @@ double expr__get_literal(const char *literal)
 		goto out;
 	}
 
+	if (!strcasecmp("#system_tsc_freq", literal)) {
+		result = system_tsc_freq();
+		goto out;
+	}
+
 	/*
 	 * Assume that topology strings are consistent, such as CPUs "0-1"
 	 * wouldn't be listed as "0,1", and so after deduplication the number of
-- 
2.35.0.rc2.247.g8bbb082509-goog