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

* [PATCH v2] perf metrics: Add literal for system TSC frequency
@ 2022-05-27  4:04 Ian Rogers
  2022-05-27  9:49 ` Peter Zijlstra
  0 siblings, 1 reply; 7+ messages in thread
From: Ian Rogers @ 2022-05-27  4:04 UTC (permalink / raw)
  To: perry.taylor, caleb.biggers, kshipra.bopardikar, Kan Liang,
	Zhengjun Xing, Peter Zijlstra, Ingo Molnar,
	Arnaldo Carvalho de Melo, Mark Rutland, Alexander Shishkin,
	Jiri Olsa, Namhyung Kim, Maxime Coquelin, Alexandre Torgue,
	Andi Kleen, James Clark, John Garry, linux-kernel,
	linux-perf-users
  Cc: Stephane Eranian, 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 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


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