Allow specifying number of iterations via --benchmark_min_time.

include/benchmark/benchmark.h

@@ -280,6 +280,9 @@ BENCHMARK(BM_test)->Unit(benchmark::kMillisecond);
 namespace benchmark {
 class BenchmarkReporter;
 
+// Default number of minimum benchmark running time in seconds.
+const char kDefaultMinTimeStr[] = "0.5s";
+
 BENCHMARK_EXPORT void PrintDefaultHelp();
 
 BENCHMARK_EXPORT void Initialize(int* argc, char** argv,
@@ -1099,11 +1102,12 @@ class BENCHMARK_EXPORT Benchmark {
   Benchmark* MinWarmUpTime(double t);
 
   // Specify the amount of iterations that should be run by this benchmark.
+  // This option overrides the `benchmark_min_time` flag.
   // REQUIRES: 'n > 0' and `MinTime` has not been called on this benchmark.
   //
   // NOTE: This function should only be used when *exact* iteration control is
   //   needed and never to control or limit how long a benchmark runs, where
-  // `--benchmark_min_time=N` or `MinTime(...)` should be used instead.
+  // `--benchmark_min_time=<N>s` or `MinTime(...)` should be used instead.
   Benchmark* Iterations(IterationCount n);
 
   // Specify the amount of times to repeat this benchmark. This option overrides
@@ -1739,6 +1743,12 @@ class BENCHMARK_EXPORT BenchmarkReporter {
   // to skip runs based on the context information.
   virtual bool ReportContext(const Context& context) = 0;
 
+  // Called once for each group of benchmark runs, gives information about
+  // the configurations of the runs.
+  virtual void ReportRunsConfig(double /*min_time*/,
+                                bool /*has_explicit_iters*/,
+                                IterationCount /*iters*/) {}
+
   // Called once for each group of benchmark runs, gives information about
   // cpu-time and heap memory usage during the benchmark run. If the group
   // of runs contained more than two entries then 'report' contains additional

src/benchmark.cc

@@ -65,12 +65,21 @@ BM_DEFINE_bool(benchmark_list_tests, false);
 // linked into the binary are run.
 BM_DEFINE_string(benchmark_filter, "");
 
-// Minimum number of seconds we should run benchmark before results are
-// considered significant.  For cpu-time based tests, this is the lower bound
+// Specification of how long to run the benchmark.
+//
+// It can be either an exact number of iterations (specified as `<integer>x`),
+// or a minimum number of seconds (specified as `<float>s`). If the latter
+// format (ie., min seconds) is used, the system may run the benchmark longer
+// until the results are considered significant.
+//
+// For backward compatibility, the `s` suffix may be omitted, in which case,
+// the specified number is interpreted as the number of seconds.
+//
+// For cpu-time based tests, this is the lower bound
 // on the total cpu time used by all threads that make up the test.  For
 // real-time based tests, this is the lower bound on the elapsed time of the
 // benchmark execution, regardless of number of threads.
-BM_DEFINE_double(benchmark_min_time, 0.5);
+BM_DEFINE_string(benchmark_min_time, kDefaultMinTimeStr);
 
 // Minimum number of seconds a benchmark should be run before results should be
 // taken into account. This e.g can be necessary for benchmarks of code which
@@ -377,6 +386,12 @@ void RunBenchmarks(const std::vector<BenchmarkInstance>& benchmarks,
       if (runner.HasRepeatsRemaining()) continue;
       // FIXME: report each repetition separately, not all of them in bulk.
 
+      display_reporter->ReportRunsConfig(
+          runner.GetMinTime(), runner.HasExplicitIters(), runner.GetIters());
+      if (file_reporter)
+        file_reporter->ReportRunsConfig(
+            runner.GetMinTime(), runner.HasExplicitIters(), runner.GetIters());
+
       RunResults run_results = runner.GetResults();
 
       // Maybe calculate complexity report
@@ -610,7 +625,7 @@ void ParseCommandLineFlags(int* argc, char** argv) {
     if (ParseBoolFlag(argv[i], "benchmark_list_tests",
                       &FLAGS_benchmark_list_tests) ||
         ParseStringFlag(argv[i], "benchmark_filter", &FLAGS_benchmark_filter) ||
-        ParseDoubleFlag(argv[i], "benchmark_min_time",
+        ParseStringFlag(argv[i], "benchmark_min_time",
                         &FLAGS_benchmark_min_time) ||
         ParseDoubleFlag(argv[i], "benchmark_min_warmup_time",
                         &FLAGS_benchmark_min_warmup_time) ||
@@ -671,7 +686,7 @@ void PrintDefaultHelp() {
           "benchmark"
           " [--benchmark_list_tests={true|false}]\n"
           "          [--benchmark_filter=<regex>]\n"
-          "          [--benchmark_min_time=<min_time>]\n"
+          "          [--benchmark_min_time=`<integer>x` OR `<float>s` ]\n"
           "          [--benchmark_min_warmup_time=<min_warmup_time>]\n"
           "          [--benchmark_repetitions=<num_repetitions>]\n"
           "          [--benchmark_enable_random_interleaving={true|false}]\n"

src/benchmark_runner.cc

@@ -28,11 +28,14 @@
 
 #include <algorithm>
 #include <atomic>
+#include <climits>
+#include <cmath>
 #include <condition_variable>
 #include <cstdio>
 #include <cstdlib>
 #include <fstream>
 #include <iostream>
+#include <limits>
 #include <memory>
 #include <string>
 #include <thread>
@@ -62,6 +65,8 @@ MemoryManager* memory_manager = nullptr;
 namespace {
 
 static constexpr IterationCount kMaxIterations = 1000000000;
+const double kDefaultMinTime =
+    std::strtod(::benchmark::kDefaultMinTimeStr, /*p_end*/ nullptr);
 
 BenchmarkReporter::Run CreateRunReport(
     const benchmark::internal::BenchmarkInstance& b,
@@ -140,23 +145,100 @@ void RunInThread(const BenchmarkInstance* b, IterationCount iters,
   manager->NotifyThreadComplete();
 }
 
+double ComputeMinTime(const benchmark::internal::BenchmarkInstance& b,
+                      const BenchTimeType& iters_or_time) {
+  if (!IsZero(b.min_time())) return b.min_time();
+  // If the flag was used to specify number of iters, then return the default
+  // min_time.
+  if (iters_or_time.tag == BenchTimeType::ITERS) return kDefaultMinTime;
+
+  return iters_or_time.time;
+}
+
+IterationCount ComputeIters(const benchmark::internal::BenchmarkInstance& b,
+                            const BenchTimeType& iters_or_time) {
+  if (b.iterations() != 0) return b.iterations();
+
+  // We've already concluded that this flag is currently used to pass
+  // iters but do a check here again anyway.
+  BM_CHECK(iters_or_time.tag == BenchTimeType::ITERS);
+  return iters_or_time.iters;
+}
+
 }  // end namespace
 
+BenchTimeType ParseBenchMinTime(const std::string& value) {
+  BenchTimeType ret;
+
+  if (value.empty()) {
+    ret.tag = BenchTimeType::TIME;
+    ret.time = 0.0;
+    return ret;
+  }
+
+  if (value.back() == 'x') {
+    const char* iters_str = value.c_str();
+    char* p_end;
+    // Reset errno before it's changed by strtol.
+    errno = 0;
+    IterationCount num_iters = std::strtol(iters_str, &p_end, 10);
+
+    // After a valid parse, p_end should have been set to
+    // point to the 'x' suffix.
+    BM_CHECK(errno == 0 && p_end != nullptr && *p_end == 'x')
+        << "Malformed iters value passed to --benchmark_min_time: `" << value
+        << "`. Expected --benchmark_min_time=<integer>x.";
+
+    ret.tag = BenchTimeType::ITERS;
+    ret.iters = num_iters;
+    return ret;
+  }
+
+  const char* time_str = value.c_str();
+  bool has_suffix = value.back() == 's';
+  if (!has_suffix) {
+    BM_VLOG(0) << "Value passed to --benchmark_min_time should have a suffix. "
+                  "Eg., `30s` for 30-seconds.";
+  }
+
+  char* p_end;
+  // Reset errno before it's changed by strtod.
+  errno = 0;
+  double min_time = std::strtod(time_str, &p_end);
+
+  // After a successfull parse, p_end should point to the suffix 's'
+  // or the end of the string, if the suffix was omitted.
+  BM_CHECK(errno == 0 && p_end != nullptr &&
+           (has_suffix && *p_end == 's' || *p_end == '\0'))
+      << "Malformed seconds value passed to --benchmark_min_time: `" << value
+      << "`. Expected --benchmark_min_time=<float>x.";
+
+  ret.tag = BenchTimeType::TIME;
+  ret.time = min_time;
+
+  return ret;
+}
+
 BenchmarkRunner::BenchmarkRunner(
     const benchmark::internal::BenchmarkInstance& b_,
     BenchmarkReporter::PerFamilyRunReports* reports_for_family_)
     : b(b_),
       reports_for_family(reports_for_family_),
-      min_time(!IsZero(b.min_time()) ? b.min_time() : FLAGS_benchmark_min_time),
+      parsed_benchtime_flag(ParseBenchMinTime(FLAGS_benchmark_min_time)),
+      min_time(ComputeMinTime(b_, parsed_benchtime_flag)),
       min_warmup_time((!IsZero(b.min_time()) && b.min_warmup_time() > 0.0)
                           ? b.min_warmup_time()
                           : FLAGS_benchmark_min_warmup_time),
       warmup_done(!(min_warmup_time > 0.0)),
       repeats(b.repetitions() != 0 ? b.repetitions()
                                    : FLAGS_benchmark_repetitions),
-      has_explicit_iteration_count(b.iterations() != 0),
+      has_explicit_iteration_count(b.iterations() != 0 ||
+                                   parsed_benchtime_flag.tag ==
+                                       BenchTimeType::ITERS),
       pool(b.threads() - 1),
-      iters(has_explicit_iteration_count ? b.iterations() : 1),
+      iters(has_explicit_iteration_count
+                ? ComputeIters(b_, parsed_benchtime_flag)
+                : 1),
       perf_counters_measurement(StrSplit(FLAGS_benchmark_perf_counters, ',')),
       perf_counters_measurement_ptr(perf_counters_measurement.IsValid()
                                         ? &perf_counters_measurement

src/benchmark_runner.h

@@ -25,7 +25,7 @@
 
 namespace benchmark {
 
-BM_DECLARE_double(benchmark_min_time);
+BM_DECLARE_string(benchmark_min_time);
 BM_DECLARE_double(benchmark_min_warmup_time);
 BM_DECLARE_int32(benchmark_repetitions);
 BM_DECLARE_bool(benchmark_report_aggregates_only);
@@ -44,6 +44,17 @@ struct RunResults {
   bool file_report_aggregates_only = false;
 };
 
+struct BENCHMARK_EXPORT BenchTimeType {
+  enum { ITERS, TIME } tag;
+  union {
+    IterationCount iters;
+    double time;
+  };
+};
+
+BENCHMARK_EXPORT
+BenchTimeType ParseBenchMinTime(const std::string& value);
+
 class BenchmarkRunner {
  public:
   BenchmarkRunner(const benchmark::internal::BenchmarkInstance& b_,
@@ -63,12 +74,19 @@ class BenchmarkRunner {
     return reports_for_family;
   }
 
+  double GetMinTime() const { return min_time; }
+
+  bool HasExplicitIters() const { return has_explicit_iteration_count; }
+
+  IterationCount GetIters() const { return iters; }
+
  private:
   RunResults run_results;
 
   const benchmark::internal::BenchmarkInstance& b;
   BenchmarkReporter::PerFamilyRunReports* reports_for_family;
 
+  BenchTimeType parsed_benchtime_flag;
   const double min_time;
   const double min_warmup_time;
   bool warmup_done;

test/BUILD

@@ -25,14 +25,14 @@ PER_SRC_COPTS = {
     "donotoptimize_test.cc": ["-O3"],
 }
 
-TEST_ARGS = ["--benchmark_min_time=0.01"]
+TEST_ARGS = ["--benchmark_min_time=0.01s"]
 
-PER_SRC_TEST_ARGS = ({
+PER_SRC_TEST_ARGS = {
     "user_counters_tabular_test.cc": ["--benchmark_counters_tabular=true"],
     "repetitions_test.cc": [" --benchmark_repetitions=3"],
-    "spec_arg_test.cc" : ["--benchmark_filter=BM_NotChosen"],
-    "spec_arg_verbosity_test.cc" : ["--v=42"],
-})
+    "spec_arg_test.cc": ["--benchmark_filter=BM_NotChosen"],
+    "spec_arg_verbosity_test.cc": ["--v=42"],
+}
 
 cc_library(
     name = "output_test_helper",
@@ -58,14 +58,14 @@ cc_library(
         copts = select({
             "//:windows": [],
             "//conditions:default": TEST_COPTS,
-        }) + PER_SRC_COPTS.get(test_src, []) ,
+        }) + PER_SRC_COPTS.get(test_src, []),
         deps = [
             ":output_test_helper",
             "//:benchmark",
             "//:benchmark_internal_headers",
             "@com_google_googletest//:gtest",
             "@com_google_googletest//:gtest_main",
-        ]
+        ],
         # FIXME: Add support for assembly tests to bazel.
         # See Issue #556
         # https://github.com/google/benchmark/issues/556
@@ -85,17 +85,17 @@ cc_test(
     size = "small",
     srcs = ["cxx03_test.cc"],
     copts = TEST_COPTS + ["-std=c++03"],
+    target_compatible_with = select({
+        "//:windows": ["@platforms//:incompatible"],
+        "//conditions:default": [],
+    }),
     deps = [
         ":output_test_helper",
         "//:benchmark",
         "//:benchmark_internal_headers",
         "@com_google_googletest//:gtest",
         "@com_google_googletest//:gtest_main",
     ],
-    target_compatible_with = select({
-        "//:windows": ["@platforms//:incompatible"],
-        "//conditions:default": [],
-    })
 )
 
 cc_test(