[PATCH v2] perf metrics: Add literal for system TSC frequency

[Ian Rogers <irogers@google.com>]

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 accurate at least on Intel
processors.

v2. Adds warnings to make clear if things have changed/broken on future
    Intel platforms. It also adds caching and an Intel specific that a
    value is computed.

[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@google.com>
---
 tools/perf/tests/expr.c | 15 +++++++++++++
 tools/perf/util/expr.c  | 50 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
index 5c0032fe93ae..45afe4f24859 100644
--- a/tools/perf/tests/expr.c
+++ b/tools/perf/tests/expr.c
@@ -1,8 +1,10 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "util/debug.h"
 #include "util/expr.h"
+#include "util/header.h"
 #include "util/smt.h"
 #include "tests.h"
+#include <math.h>
 #include <stdlib.h>
 #include <string.h>
 #include <linux/zalloc.h>
@@ -69,6 +71,11 @@ static int test__expr(struct test_suite *t __maybe_unused, int subtest __maybe_u
 	double val, num_cpus, num_cores, num_dies, num_packages;
 	int ret;
 	struct expr_parse_ctx *ctx;
+	bool is_intel = false;
+	char buf[128];
+
+	if (!get_cpuid(buf, sizeof(buf)))
+		is_intel = strstr(buf, "Intel") != NULL;
 
 	TEST_ASSERT_EQUAL("ids_union", test_ids_union(), 0);
 
@@ -175,6 +182,14 @@ static int test__expr(struct test_suite *t __maybe_unused, int subtest __maybe_u
 	if (num_dies) // Some platforms do not have CPU die support, for example s390
 		TEST_ASSERT_VAL("#num_dies >= #num_packages", num_dies >= num_packages);
 
+	if (is_intel) {
+		double system_tsc_freq;
+
+		TEST_ASSERT_VAL("#system_tsc_freq", expr__parse(&system_tsc_freq, ctx,
+								"#system_tsc_freq") == 0);
+		TEST_ASSERT_VAL("!isnan(#system_tsc_freq)", !isnan(system_tsc_freq));
+	}
+
 	/*
 	 * Source count returns the number of events aggregating in a leader
 	 * event including the leader. Check parsing yields an id.
diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
index 675f318ce7c1..f33aeb1e6faa 100644
--- a/tools/perf/util/expr.c
+++ b/tools/perf/util/expr.c
@@ -402,6 +402,51 @@ 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)
+{
+	static double result;
+	static bool computed;
+	FILE *cpuinfo;
+	char *line = NULL;
+	size_t len = 0;
+
+	if (computed)
+		return result;
+
+	computed = true;
+	result = NAN;
+	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 (isnan(result))
+		pr_err("Failed to find TSC frequency in /proc/cpuinfo");
+
+	free(line);
+	fclose(cpuinfo);
+	return result;
+}
+
 double expr__get_literal(const char *literal)
 {
 	static struct cpu_topology *topology;
@@ -417,6 +462,11 @@ 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
-- 
2.36.1.124.g0e6072fb45-goog