add a benchmark for standard std::chrono clocks

Summary:
Querying clocks has a cost. Add a microbenchmark for measuring that
cost on all platforms.

Reviewed By: genevievehelsel

Differential Revision: D42182073

fbshipit-source-id: facb907fc4abed74625e0e28fe3ab63d8335a9fd

eden/fs/benchmarks/language/clock.cpp

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This software may be used and distributed according to the terms of the
+ * GNU General Public License version 2.
+ */
+
+#include <chrono>
+#include "eden/common/utils/benchharness/Bench.h"
+
+namespace {
+
+using namespace benchmark;
+using namespace facebook::eden;
+
+void system_clock(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::chrono::system_clock::now());
+  }
+}
+BENCHMARK(system_clock);
+
+void steady_clock(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::chrono::steady_clock::now());
+  }
+}
+BENCHMARK(steady_clock);
+
+void high_resolution_clock(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::chrono::high_resolution_clock::now());
+  }
+}
+BENCHMARK(high_resolution_clock);
+
+} // namespace