Small benchmark for coarse_steady_clock

Summary: [Folly] Small benchmark for `coarse_steady_clock`.

Differential Revision: D22320499

fbshipit-source-id: dbd93e886b9e984d7469288258eefaa4a3fafb10

folly/test/ChronoBench.cpp

+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <atomic>
+#include <chrono>
+
+#include <folly/Benchmark.h>
+#include <folly/Chrono.h>
+#include <folly/chrono/Hardware.h>
+#include <folly/hash/Hash.h>
+#include <folly/init/Init.h>
+
+BENCHMARK(steady_clock_now, iters) {
+  uint64_t r = 0;
+  while (iters--) {
+    using clock = std::chrono::steady_clock;
+    auto const s = clock::now().time_since_epoch().count();
+    r = folly::hash::twang_mix64(r ^ s);
+  }
+  folly::doNotOptimizeAway(r);
+}
+
+BENCHMARK(coarse_steady_clock_now, iters) {
+  uint64_t r = 0;
+  while (iters--) {
+    using clock = folly::chrono::coarse_steady_clock;
+    auto const s = clock::now().time_since_epoch().count();
+    r = folly::hash::twang_mix64(r ^ s);
+  }
+  folly::doNotOptimizeAway(r);
+}
+
+BENCHMARK(hardware_timestamp_unserialized, iters) {
+  uint64_t r = 0;
+  while (iters--) {
+    auto const s = folly::hardware_timestamp();
+    r = folly::hash::twang_mix64(r ^ s);
+  }
+  folly::doNotOptimizeAway(r);
+}
+
+BENCHMARK(atomic_load_relaxed, iters) {
+  std::atomic<uint64_t> now{0};
+  uint64_t r = 0;
+  while (iters--) {
+    auto const s = now.load(std::memory_order_relaxed);
+    r = folly::hash::twang_mix64(r ^ s);
+  }
+  folly::doNotOptimizeAway(r);
+}
+
+int main(int argc, char** argv) {
+  folly::Init init(&argc, &argv);
+  folly::runBenchmarks();
+  return 0;
+}