Implementation of random interleaving. (#1105)

README.md

@@ -180,7 +180,7 @@ BENCHMARK_MAIN();
 ```
 
 To run the benchmark, compile and link against the `benchmark` library
-(libbenchmark.a/.so). If you followed the build steps above, this library will 
+(libbenchmark.a/.so). If you followed the build steps above, this library will
 be under the build directory you created.
 
 ```bash
@@ -300,6 +300,8 @@ too (`-lkstat`).
 
 [Setting the Time Unit](#setting-the-time-unit)
 
+[Random Interleaving](docs/random_interleaving.md)
+
 [User-Requested Performance Counters](docs/perf_counters.md)
 
 [Preventing Optimization](#preventing-optimization)
@@ -400,8 +402,8 @@ Write benchmark results to a file with the `--benchmark_out=<filename>` option
 (or set `BENCHMARK_OUT`). Specify the output format with
 `--benchmark_out_format={json|console|csv}` (or set
 `BENCHMARK_OUT_FORMAT={json|console|csv}`). Note that the 'csv' reporter is
-deprecated and the saved `.csv` file 
-[is not parsable](https://github.com/google/benchmark/issues/794) by csv 
+deprecated and the saved `.csv` file
+[is not parsable](https://github.com/google/benchmark/issues/794) by csv
 parsers.
 
 Specifying `--benchmark_out` does not suppress the console output.

docs/random_interleaving.md

+<a name="interleaving" />
+
+# Random Interleaving
+
+[Random Interleaving](https://github.com/google/benchmark/issues/1051) is a
+technique to lower run-to-run variance. It breaks the execution of a
+microbenchmark into multiple chunks and randomly interleaves them with chunks
+from other microbenchmarks in the same benchmark test. Data shows it is able to
+lower run-to-run variance by
+[40%](https://github.com/google/benchmark/issues/1051) on average.
+
+To use, set `--benchmark_enable_random_interleaving=true`.
+
+It's a known issue that random interleaving may increase the benchmark execution
+time, if:
+
+1.  A benchmark has costly setup and / or teardown. Random interleaving will run
+    setup and teardown many times and may increase test execution time
+    significantly.
+2.  The time to run a single benchmark iteration is larger than the desired time
+    per repetition (i.e., `benchmark_min_time / benchmark_repetitions`).
+
+The overhead of random interleaving can be controlled by
+`--benchmark_random_interleaving_max_overhead`. The default value is 0.4 meaning
+the total execution time under random interlaving is limited by 1.4 x original
+total execution time. Set it to `inf` for unlimited overhead.

src/benchmark_adjust_repetitions.cc

+// Copyright 2015 Google Inc. All rights reserved.
+//
+// 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 "benchmark_adjust_repetitions.h"
+
+#include "benchmark_api_internal.h"
+#include "log.h"
+
+namespace benchmark {
+namespace internal {
+
+namespace {
+
+constexpr double kNanosecondInSecond = 1e-9;
+
+}  // namespace
+
+int ComputeRandomInterleavingRepetitions(
+    InternalRandomInterleavingRepetitionsInput input) {
+  // Find the repetitions such that total overhead is bounded. Let
+  //   n = desired number of repetitions, i.e., the output of this method.
+  //   t = total real execution time per repetition including overhead,
+  //       (input.total_execution_time_per_repetition).
+  //   o = maximum allowed increase in total real execution time due to random
+  //       interleaving, measured as a fraction (input.max_overhead).
+  //   e = estimated total execution time without Random Interleaving
+  // We want
+  //   t * n / e <= 1 + o
+  // I.e.,
+  //   n <= (1 + o) * e / t
+  //
+  // Let
+  //   h = overhead per repetition, which include all setup / teardown time and
+  //       also the execution time of preliminary trials used to search for the
+  //       correct number of iterations.
+  //   r = real execution time per repetition not including overhead
+  //       (input.real_accumulated_time_per_repetition).
+  //   s = measured execution time per repetition not including overhead,
+  //       which can be either real or CPU time
+  //       (input.accumulated_time_per_repetition).
+  // We have
+  //   h = t - r
+  //
+  // Let
+  //   m = total minimum measured execution time for all repetitions
+  //       (input.min_time_per_repetition * input.max_repetitions).
+  // Let
+  //   f = m / s
+  // f is the scale factor between m and s, and will be used to estimate
+  // l, the total real execution time for all repetitions excluding the
+  // overhead. It's reasonable to assume that the real execution time excluding
+  // the overhead is proportional to the measured time. Hence we expect to see
+  // l / r to be equal to m / s. That is, l / r = f, thus, l = r * f. Then the
+  // total execution time e can be estimated by h + l, which is h + r * f.
+  //   e = h + r * f
+  // Note that this might be an underestimation. If number of repetitions is
+  // reduced, we may need to run more iterations per repetition, and that may
+  // increase the number of preliminary trials needed to find the correct
+  // number of iterations.
+
+  double h = std::max(0.0, input.total_execution_time_per_repetition -
+                               input.real_time_used_per_repetition);
+  double r =
+      std::max(input.real_time_used_per_repetition, kNanosecondInSecond);
+  double s =
+      std::max(input.time_used_per_repetition, kNanosecondInSecond);
+  double m = input.min_time_per_repetition * input.max_repetitions;
+
+  // f = m / s
+  // RunBenchmark() always overshoot the iteration count by kSafetyMultiplier.
+  // Apply the same factor here.
+  //   f = kSafetyMultiplier * m / s
+  // Also we want to make sure 1 <= f <= input.max_repetitions. Note that we
+  // may not be able to reach m because the total iters per repetition is
+  // upper bounded by --benchmark_max_iters. This behavior is preserved in
+  // Random Interleaving, as we won't run repetitions more than
+  // input.max_repetitions to reach m.
+
+  double f = kSafetyMultiplier * m / s;
+  f = std::min(std::max(f, 1.0), static_cast<double>(input.max_repetitions));
+
+  double e = h + r * f;
+  // n <= (1 + o) * e / t = (1 + o) * e / (h + r)
+  // Also we want to make sure 1 <= n <= input.max_repetition, and (h + r) > 0.
+  double n = (1 + input.max_overhead) * e / (h + r);
+  n = std::min(std::max(n, 1.0), static_cast<double>(input.max_repetitions));
+
+  int n_int = static_cast<int>(n);
+
+  VLOG(2) << "Computed random interleaving repetitions"
+          << "\n  input.total_execution_time_per_repetition: "
+          << input.total_execution_time_per_repetition
+          << "\n  input.time_used_per_repetition: "
+          << input.time_used_per_repetition
+          << "\n  input.real_time_used_per_repetition: "
+          << input.real_time_used_per_repetition
+          << "\n  input.min_time_per_repetitions: "
+          << input.min_time_per_repetition
+          << "\n  input.max_repetitions: " << input.max_repetitions
+          << "\n  input.max_overhead: " << input.max_overhead
+          << "\n  h: " << h
+          << "\n  r: " << r
+          << "\n  s: " << s
+          << "\n  f: " << f
+          << "\n  m: " << m
+          << "\n  e: " << e
+          << "\n  n: " << n
+          << "\n  n_int: " << n_int;
+
+  return n_int;
+}
+
+}  // internal
+}  // benchmark

src/benchmark_adjust_repetitions.h

+// Copyright 2015 Google Inc. All rights reserved.
+//
+// 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.
+
+#ifndef BENCHMARK_ADJUST_REPETITIONS_H
+#define BENCHMARK_ADJUST_REPETITIONS_H
+
+#include "benchmark/benchmark.h"
+#include "commandlineflags.h"
+
+namespace benchmark {
+namespace internal {
+
+// Defines the input tuple to ComputeRandomInterleavingRepetitions().
+struct InternalRandomInterleavingRepetitionsInput {
+  double total_execution_time_per_repetition;
+  double time_used_per_repetition;
+  double real_time_used_per_repetition;
+  double min_time_per_repetition;
+  double max_overhead;
+  int max_repetitions;
+};
+
+// Should be called right after the first repetition is completed to estimate
+// the number of iterations.
+int ComputeRandomInterleavingRepetitions(
+    InternalRandomInterleavingRepetitionsInput input);
+
+}  // end namespace internal
+}  // end namespace benchmark
+
+#endif  // BENCHMARK_ADJUST_REPETITIONS_H

src/benchmark_api_internal.cc

@@ -2,8 +2,11 @@
 
 #include <cinttypes>
 
+#include "check.h"
 #include "string_util.h"
 
+DECLARE_bool(benchmark_enable_random_interleaving);
+
 namespace benchmark {
 namespace internal {
 
@@ -21,9 +24,12 @@ BenchmarkInstance::BenchmarkInstance(Benchmark* benchmark,
       complexity_lambda_(benchmark_.complexity_lambda_),
       statistics_(benchmark_.statistics_),
       repetitions_(benchmark_.repetitions_),
-      min_time_(benchmark_.min_time_),
+      min_time_(!IsZero(benchmark_.min_time_) ? benchmark_.min_time_
+                                              : GetMinTime()),
       iterations_(benchmark_.iterations_),
       threads_(thread_count) {
+  CHECK(!IsZero(min_time_)) << "min_time must be non-zero.";
+
   name_.function_name = benchmark_.name_;
 
   size_t arg_i = 0;
@@ -77,6 +83,32 @@ BenchmarkInstance::BenchmarkInstance(Benchmark* benchmark,
   }
 }
 
+double BenchmarkInstance::MinTime() const {
+  if (FLAGS_benchmark_enable_random_interleaving) {
+    // Random Interleaving will automatically adjust
+    // random_interleaving_repetitions(). Dividing
+    // total execution time by random_interleaving_repetitions() gives
+    // the adjusted min_time per repetition.
+    return min_time_ * GetRepetitions() / RandomInterleavingRepetitions();
+  }
+  return min_time_;
+}
+
+int BenchmarkInstance::RandomInterleavingRepetitions() const {
+  return random_interleaving_repetitions_ < 0
+             ? GetRepetitions()
+             : random_interleaving_repetitions_;
+}
+
+bool BenchmarkInstance::RandomInterleavingRepetitionsInitialized() const {
+  return random_interleaving_repetitions_ >= 0;
+}
+
+void BenchmarkInstance::InitRandomInterleavingRepetitions(
+    int reps) const {
+  random_interleaving_repetitions_ = reps;
+}
+
 State BenchmarkInstance::Run(
     IterationCount iters, int thread_id, internal::ThreadTimer* timer,
     internal::ThreadManager* manager,

src/benchmark_api_internal.h

 #ifndef BENCHMARK_API_INTERNAL_H
 #define BENCHMARK_API_INTERNAL_H
 
+#include "benchmark/benchmark.h"
+#include "commandlineflags.h"
+
+#include <chrono>
 #include <cmath>
 #include <iosfwd>
 #include <limits>
@@ -14,12 +18,25 @@
 namespace benchmark {
 namespace internal {
 
+extern const double kSafetyMultiplier;
+
 // Information kept per benchmark we may want to run
 class BenchmarkInstance {
  public:
   BenchmarkInstance(Benchmark* benchmark, const std::vector<int64_t>& args,
                     int threads);
 
+  // Returns number of repetitions for Random Interleaving. This will be
+  // initialized later once we finish the first repetition, if Random
+  // Interleaving is enabled. See also ComputeRandominterleavingrepetitions().
+  int RandomInterleavingRepetitions() const;
+
+  // Returns true if repetitions for Random Interleaving is initialized.
+  bool RandomInterleavingRepetitionsInitialized() const;
+
+  // Initializes number of repetitions for random interleaving.
+  void InitRandomInterleavingRepetitions(int reps) const;
+
   const BenchmarkName& name() const { return name_; }
   AggregationReportMode aggregation_report_mode() const {
     return aggregation_report_mode_;
@@ -32,7 +49,7 @@ class BenchmarkInstance {
   BigOFunc& complexity_lambda() const { return *complexity_lambda_; }
   const std::vector<Statistics>& statistics() const { return statistics_; }
   int repetitions() const { return repetitions_; }
-  double min_time() const { return min_time_; }
+  double MinTime() const;
   IterationCount iterations() const { return iterations_; }
   int threads() const { return threads_; }
 
@@ -53,12 +70,13 @@ class BenchmarkInstance {
   bool use_manual_time_;
   BigO complexity_;
   BigOFunc* complexity_lambda_;
-  UserCounters counters_;
-  const std::vector<Statistics>& statistics_;
+  std::vector<Statistics> statistics_;
   int repetitions_;
   double min_time_;
   IterationCount iterations_;
-  int threads_;  // Number of concurrent threads to us
+  int threads_;
+  UserCounters counters_;
+  mutable int random_interleaving_repetitions_ = -1;
 };
 
 bool FindBenchmarksInternal(const std::string& re,
@@ -69,6 +87,10 @@ bool IsZero(double n);
 
 ConsoleReporter::OutputOptions GetOutputOptions(bool force_no_color = false);
 
+double GetMinTime();
+
+int GetRepetitions();
+
 }  // end namespace internal
 }  // end namespace benchmark
 

src/benchmark_runner.cc

@@ -15,6 +15,7 @@
 #include "benchmark_runner.h"
 #include "benchmark/benchmark.h"
 #include "benchmark_api_internal.h"
+#include "benchmark_adjust_repetitions.h"
 #include "internal_macros.h"
 
 #ifndef BENCHMARK_OS_WINDOWS
@@ -52,6 +53,9 @@
 #include "thread_manager.h"
 #include "thread_timer.h"
 
+DECLARE_bool(benchmark_enable_random_interleaving);
+DECLARE_double(benchmark_random_interleaving_max_overhead);
+
 namespace benchmark {
 
 namespace internal {
@@ -67,7 +71,7 @@ BenchmarkReporter::Run CreateRunReport(
     const internal::ThreadManager::Result& results,
     IterationCount memory_iterations,
     const MemoryManager::Result& memory_result, double seconds,
-    int64_t repetition_index) {
+    int repetition_index) {
   // Create report about this benchmark run.
   BenchmarkReporter::Run report;
 
@@ -138,12 +142,16 @@ void RunInThread(const BenchmarkInstance* b, IterationCount iters,
 class BenchmarkRunner {
  public:
   BenchmarkRunner(const benchmark::internal::BenchmarkInstance& b_,
-                  std::vector<BenchmarkReporter::Run>* complexity_reports_)
+                  int outer_repetitions_,
+                  int inner_repetitions_,
+                  std::vector<BenchmarkReporter::Run>* complexity_reports_,
+                  RunResults* run_results_)
       : b(b_),
         complexity_reports(*complexity_reports_),
-        min_time(!IsZero(b.min_time()) ? b.min_time() : FLAGS_benchmark_min_time),
-        repeats(b.repetitions() != 0 ? b.repetitions()
-                                   : FLAGS_benchmark_repetitions),
+        run_results(*run_results_),
+        outer_repetitions(outer_repetitions_),
+        inner_repetitions(inner_repetitions_),
+        repeats(b.repetitions() != 0 ? b.repetitions() : inner_repetitions),
         has_explicit_iteration_count(b.iterations() != 0),
         pool(b.threads() - 1),
         iters(has_explicit_iteration_count ? b.iterations() : 1),
@@ -163,6 +171,7 @@ class BenchmarkRunner {
            internal::ARM_DisplayReportAggregatesOnly);
       run_results.file_report_aggregates_only =
           (b.aggregation_report_mode() & internal::ARM_FileReportAggregatesOnly);
+
       CHECK(FLAGS_benchmark_perf_counters.empty() ||
             perf_counters_measurement.IsValid())
           << "Perf counters were requested but could not be set up.";
@@ -179,21 +188,20 @@ class BenchmarkRunner {
     if ((b.complexity() != oNone) && b.last_benchmark_instance) {
       auto additional_run_stats = ComputeBigO(complexity_reports);
       run_results.aggregates_only.insert(run_results.aggregates_only.end(),
-                                         additional_run_stats.begin(),
-                                         additional_run_stats.end());
+                                          additional_run_stats.begin(),
+                                          additional_run_stats.end());
       complexity_reports.clear();
     }
   }
 
-  RunResults&& get_results() { return std::move(run_results); }
-
  private:
-  RunResults run_results;
-
   const benchmark::internal::BenchmarkInstance& b;
   std::vector<BenchmarkReporter::Run>& complexity_reports;
 
-  const double min_time;
+  RunResults& run_results;
+
+  const int outer_repetitions;
+  const int inner_repetitions;
   const int repeats;
   const bool has_explicit_iteration_count;
 
@@ -268,13 +276,14 @@ class BenchmarkRunner {
   IterationCount PredictNumItersNeeded(const IterationResults& i) const {
     // See how much iterations should be increased by.
     // Note: Avoid division by zero with max(seconds, 1ns).
-    double multiplier = min_time * 1.4 / std::max(i.seconds, 1e-9);
+    double multiplier =
+        b.MinTime() * kSafetyMultiplier / std::max(i.seconds, 1e-9);
     // If our last run was at least 10% of FLAGS_benchmark_min_time then we
     // use the multiplier directly.
     // Otherwise we use at most 10 times expansion.
     // NOTE: When the last run was at least 10% of the min time the max
     // expansion should be 14x.
-    bool is_significant = (i.seconds / min_time) > 0.1;
+    bool is_significant = (i.seconds / b.MinTime()) > 0.1;
     multiplier = is_significant ? multiplier : std::min(10.0, multiplier);
     if (multiplier <= 1.0) multiplier = 2.0;
 
@@ -295,14 +304,17 @@ class BenchmarkRunner {
     // or because an error was reported.
     return i.results.has_error_ ||
            i.iters >= kMaxIterations ||  // Too many iterations already.
-           i.seconds >= min_time ||      // The elapsed time is large enough.
-           // CPU time is specified but the elapsed real time greatly exceeds
-           // the minimum time.
-           // Note that user provided timers are except from this sanity check.
-           ((i.results.real_time_used >= 5 * min_time) && !b.use_manual_time());
+           i.seconds >= b.MinTime() ||   // The elapsed time is large enough.
+                                         // CPU time is specified but the
+                                         // elapsed real time greatly exceeds
+                                         // the minimum time. Note that user
+                                         // provided timers are except from this
+                                         // sanity check.
+           ((i.results.real_time_used >= 5 * b.MinTime()) &&
+            !b.use_manual_time());
   }
 
-  void DoOneRepetition(int64_t repetition_index) {
+  void DoOneRepetition(int repetition_index) {
     const bool is_the_first_repetition = repetition_index == 0;
     IterationResults i;
 
@@ -312,8 +324,10 @@ class BenchmarkRunner {
     // Please do note that the if there are repetitions, the iteration count
     // is *only* calculated for the *first* repetition, and other repetitions
     // simply use that precomputed iteration count.
+    const auto exec_start = benchmark::ChronoClockNow();
     for (;;) {
       i = DoNIterations();
+      const auto exec_end = benchmark::ChronoClockNow();
 
       // Do we consider the results to be significant?
       // If we are doing repetitions, and the first repetition was already done,
@@ -324,7 +338,38 @@ class BenchmarkRunner {
                                            has_explicit_iteration_count ||
                                            ShouldReportIterationResults(i);
 
-      if (results_are_significant) break;  // Good, let's report them!
+      if (results_are_significant) {
+        // The number of repetitions for random interleaving may be reduced
+        // to limit the increase in benchmark execution time. When this happens
+        // the target execution time for each repetition is increased. We may
+        // need to rerun trials to calculate iters according to the increased
+        // target execution time.
+        bool rerun_trial = false;
+        // If random interleaving is enabled and the repetitions is not
+        // initialized, do it now.
+        if (FLAGS_benchmark_enable_random_interleaving &&
+            !b.RandomInterleavingRepetitionsInitialized()) {
+          InternalRandomInterleavingRepetitionsInput input;
+          input.total_execution_time_per_repetition = exec_end - exec_start;
+          input.time_used_per_repetition = i.seconds;
+          input.real_time_used_per_repetition = i.results.real_time_used;
+          input.min_time_per_repetition = GetMinTime();
+          input.max_overhead = FLAGS_benchmark_random_interleaving_max_overhead;
+          input.max_repetitions = GetRepetitions();
+          b.InitRandomInterleavingRepetitions(
+              ComputeRandomInterleavingRepetitions(input));
+          // If the number of repetitions changed, need to rerun the last trial
+          // because iters may also change. Note that we only need to do this
+          // if accumulated_time < b.MinTime(), i.e., the iterations we have
+          // run is not enough for the already adjusted b.MinTime().
+          // Otherwise, we will still skip the rerun.
+          rerun_trial =
+              b.RandomInterleavingRepetitions() < GetRepetitions() &&
+              i.seconds < b.MinTime() && !has_explicit_iteration_count;
+        }
+
+        if (!rerun_trial) break;  // Good, let's report them!
+      }
 
       // Nope, bad iteration. Let's re-estimate the hopefully-sufficient
       // iteration count, and run the benchmark again...
@@ -341,7 +386,8 @@ class BenchmarkRunner {
     if (memory_manager != nullptr) {
       // Only run a few iterations to reduce the impact of one-time
       // allocations in benchmarks that are not properly managed.
-      memory_iterations = std::min<IterationCount>(16, iters);
+      memory_iterations = std::min<IterationCount>(
+          16 / outer_repetitions + (16 % outer_repetitions != 0), iters);
       memory_manager->Start();
       std::unique_ptr<internal::ThreadManager> manager;
       manager.reset(new internal::ThreadManager(1));
@@ -367,11 +413,12 @@ class BenchmarkRunner {
 
 }  // end namespace
 
-RunResults RunBenchmark(
-    const benchmark::internal::BenchmarkInstance& b,
-    std::vector<BenchmarkReporter::Run>* complexity_reports) {
-  internal::BenchmarkRunner r(b, complexity_reports);
-  return r.get_results();
+void RunBenchmark(const benchmark::internal::BenchmarkInstance& b,
+                  const int outer_repetitions, const int inner_repetitions,
+                  std::vector<BenchmarkReporter::Run>* complexity_reports,
+                  RunResults* run_results) {
+  internal::BenchmarkRunner r(b, outer_repetitions, inner_repetitions,
+                              complexity_reports, run_results);
 }
 
 }  // end namespace internal

src/benchmark_runner.h

@@ -42,9 +42,10 @@ struct RunResults {
   bool file_report_aggregates_only = false;
 };
 
-RunResults RunBenchmark(
-    const benchmark::internal::BenchmarkInstance& b,
-    std::vector<BenchmarkReporter::Run>* complexity_reports);
+void RunBenchmark(const benchmark::internal::BenchmarkInstance& b,
+                  int outer_repetitions, int inner_repetitions,
+                  std::vector<BenchmarkReporter::Run>* complexity_reports,
+                  RunResults* run_results);
 
 }  // namespace internal
 

test/CMakeLists.txt

@@ -196,6 +196,7 @@ if (BENCHMARK_ENABLE_GTEST_TESTS)
 
   add_gtest(benchmark_gtest)
   add_gtest(benchmark_name_gtest)
+  add_gtest(benchmark_random_interleaving_gtest)
   add_gtest(commandlineflags_gtest)
   add_gtest(statistics_gtest)
   add_gtest(string_util_gtest)

test/benchmark_random_interleaving_gtest.cc

+#include <queue>
+#include <string>
+#include <vector>
+
+#include "../src/benchmark_adjust_repetitions.h"
+#include "../src/string_util.h"
+#include "benchmark/benchmark.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+DECLARE_bool(benchmark_enable_random_interleaving);
+DECLARE_string(benchmark_filter);
+DECLARE_double(benchmark_random_interleaving_max_overhead);
+
+namespace do_not_read_flag_directly {
+DECLARE_int32(benchmark_repetitions);
+}  // namespace do_not_read_flag_directly
+
+namespace benchmark {
+namespace internal {
+namespace {
+
+class EventQueue : public std::queue<std::string> {
+ public:
+  void Put(const std::string& event) {
+    push(event);
+  }
+
+  void Clear() {
+    while (!empty()) {
+      pop();
+    }
+  }
+
+  std::string Get() {
+    std::string event = front();
+    pop();
+    return event;
+  }
+};
+
+static EventQueue* queue = new EventQueue;
+
+class NullReporter : public BenchmarkReporter {
+ public:
+  bool ReportContext(const Context& /*context*/) override {
+    return true;
+  }
+  void ReportRuns(const std::vector<Run>& /* report */) override {}
+};
+
+class BenchmarkTest : public testing::Test {
+ public:
+  static void SetupHook(int /* num_threads */) { queue->push("Setup"); }
+
+  static void TeardownHook(int /* num_threads */) { queue->push("Teardown"); }
+
+  void Execute(const std::string& pattern) {
+    queue->Clear();
+
+    BenchmarkReporter* reporter = new NullReporter;
+    FLAGS_benchmark_filter = pattern;
+    RunSpecifiedBenchmarks(reporter);
+    delete reporter;
+
+    queue->Put("DONE");  // End marker
+  }
+};
+
+static void BM_Match1(benchmark::State& state) {
+  const int64_t arg = state.range(0);
+
+  for (auto _ : state) {}
+  queue->Put(StrFormat("BM_Match1/%d", static_cast<int>(arg)));
+}
+BENCHMARK(BM_Match1)
+    ->Iterations(100)
+    ->Arg(1)
+    ->Arg(2)
+    ->Arg(3)
+    ->Range(10, 80)
+    ->Args({90})
+    ->Args({100});
+
+static void BM_MatchOverhead(benchmark::State& state) {
+  const int64_t arg = state.range(0);
+
+  for (auto _ : state) {}
+  queue->Put(StrFormat("BM_MatchOverhead/%d", static_cast<int>(arg)));
+}
+BENCHMARK(BM_MatchOverhead)
+    ->Iterations(100)
+    ->Arg(64)
+    ->Arg(80);
+
+TEST_F(BenchmarkTest, Match1) {
+  Execute("BM_Match1");
+  ASSERT_EQ("BM_Match1/1", queue->Get());
+  ASSERT_EQ("BM_Match1/2", queue->Get());
+  ASSERT_EQ("BM_Match1/3", queue->Get());
+  ASSERT_EQ("BM_Match1/10", queue->Get());
+  ASSERT_EQ("BM_Match1/64", queue->Get());
+  ASSERT_EQ("BM_Match1/80", queue->Get());
+  ASSERT_EQ("BM_Match1/90", queue->Get());
+  ASSERT_EQ("BM_Match1/100", queue->Get());
+  ASSERT_EQ("DONE", queue->Get());
+}
+
+TEST_F(BenchmarkTest, Match1WithRepetition) {
+  do_not_read_flag_directly::FLAGS_benchmark_repetitions = 2;
+
+  Execute("BM_Match1/(64|80)");
+  ASSERT_EQ("BM_Match1/64", queue->Get());
+  ASSERT_EQ("BM_Match1/64", queue->Get());
+  ASSERT_EQ("BM_Match1/80", queue->Get());
+  ASSERT_EQ("BM_Match1/80", queue->Get());
+  ASSERT_EQ("DONE", queue->Get());
+}
+
+TEST_F(BenchmarkTest, Match1WithRandomInterleaving) {
+  FLAGS_benchmark_enable_random_interleaving = true;
+  do_not_read_flag_directly::FLAGS_benchmark_repetitions = 100;
+  FLAGS_benchmark_random_interleaving_max_overhead =
+      std::numeric_limits<double>::infinity();
+
+  std::vector<std::string> expected({"BM_Match1/64", "BM_Match1/80"});
+  std::map<std::string, int> interleaving_count;
+  Execute("BM_Match1/(64|80)");
+  for (int i = 0; i < 100; ++i) {
+    std::vector<std::string> interleaving;
+    interleaving.push_back(queue->Get());
+    interleaving.push_back(queue->Get());
+    EXPECT_THAT(interleaving, testing::UnorderedElementsAreArray(expected));
+    interleaving_count[StrFormat("%s,%s", interleaving[0].c_str(),
+                                 interleaving[1].c_str())]++;
+  }
+  EXPECT_GE(interleaving_count.size(), 2) << "Interleaving was not randomized.";
+  ASSERT_EQ("DONE", queue->Get());
+}
+
+TEST_F(BenchmarkTest, Match1WithRandomInterleavingAndZeroOverhead) {
+  FLAGS_benchmark_enable_random_interleaving = true;
+  do_not_read_flag_directly::FLAGS_benchmark_repetitions = 100;
+  FLAGS_benchmark_random_interleaving_max_overhead = 0;
+
+  // ComputeRandomInterleavingRepetitions() will kick in and rerun each
+  // benchmark once with increased iterations. Then number of repetitions will
+  // be reduced to < 100. The first 4 executions should be
+  // 2 x BM_MatchOverhead/64 and 2 x BM_MatchOverhead/80.
+  std::vector<std::string> expected(
+      {"BM_MatchOverhead/64", "BM_MatchOverhead/80", "BM_MatchOverhead/64",
+       "BM_MatchOverhead/80"});
+  std::map<std::string, int> interleaving_count;
+  Execute("BM_MatchOverhead/(64|80)");
+  std::vector<std::string> interleaving;
+  interleaving.push_back(queue->Get());
+  interleaving.push_back(queue->Get());
+  interleaving.push_back(queue->Get());
+  interleaving.push_back(queue->Get());
+  EXPECT_THAT(interleaving, testing::UnorderedElementsAreArray(expected));
+  ASSERT_LT(queue->size(), 100) << "# Repetitions was not reduced to < 100.";
+}
+
+InternalRandomInterleavingRepetitionsInput CreateInput(
+    double total, double time, double real_time, double min_time,
+    double overhead, int repetitions) {
+  InternalRandomInterleavingRepetitionsInput input;
+  input.total_execution_time_per_repetition = total;
+  input.time_used_per_repetition = time;
+  input.real_time_used_per_repetition = real_time;
+  input.min_time_per_repetition = min_time;
+  input.max_overhead = overhead;
+  input.max_repetitions = repetitions;
+  return input;
+}
+
+TEST(Benchmark, ComputeRandomInterleavingRepetitions) {
+  // On wall clock time.
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.05, 0.05, 0.05, 0.05, 0.0, 10)),
+            10);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.05, 0.05, 0.05, 0.05, 0.4, 10)),
+            10);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.06, 0.05, 0.05, 0.05, 0.0, 10)),
+            8);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.06, 0.05, 0.05, 0.05, 0.4, 10)),
+            10);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.08, 0.05, 0.05, 0.05, 0.0, 10)),
+            6);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.08, 0.05, 0.05, 0.05, 0.4, 10)),
+            9);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.26, 0.25, 0.25, 0.05, 0.0, 10)),
+            2);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.25, 0.25, 0.25, 0.05, 0.4, 10)),
+            3);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.26, 0.25, 0.25, 0.05, 0.0, 10)),
+            2);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.26, 0.25, 0.25, 0.05, 0.4, 10)),
+            3);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.38, 0.25, 0.25, 0.05, 0.0, 10)),
+            2);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.38, 0.25, 0.25, 0.05, 0.4, 10)),
+            3);
+
+  // On CPU time.
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.1, 0.05, 0.1, 0.05, 0.0, 10)),
+            10);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.1, 0.05, 0.1, 0.05, 0.4, 10)),
+            10);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.11, 0.05, 0.1, 0.05, 0.0, 10)),
+            9);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.11, 0.05, 0.1, 0.05, 0.4, 10)),
+            10);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.15, 0.05, 0.1, 0.05, 0.0, 10)),
+            7);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.15, 0.05, 0.1, 0.05, 0.4, 10)),
+            9);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.5, 0.25, 0.5, 0.05, 0.0, 10)),
+            2);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.5, 0.25, 0.5, 0.05, 0.4, 10)),
+            3);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.51, 0.25, 0.5, 0.05, 0.0, 10)),
+            2);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.51, 0.25, 0.5, 0.05, 0.4, 10)),
+            3);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.8, 0.25, 0.5, 0.05, 0.0, 10)),
+            2);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.8, 0.25, 0.5, 0.05, 0.4, 10)),
+            2);
+
+  // Corner cases.
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.0, 0.25, 0.5, 0.05, 0.4, 10)),
+            3);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.8, 0.0, 0.5, 0.05, 0.4, 10)),
+            9);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.8, 0.25, 0.0, 0.05, 0.4, 10)),
+            1);
+  EXPECT_EQ(ComputeRandomInterleavingRepetitions(
+                CreateInput(0.8, 0.25, 0.5, 0.0, 0.4, 10)),
+            1);
+}
+
+}  // namespace
+}  // namespace internal
+}  // namespace benchmark