Fix minimum benchmark time with multiple threads

Closes #2117

Author: hahnjo

src/benchmark_runner.cc

@@ -123,12 +123,7 @@ BenchmarkReporter::Run CreateRunReport(
               : 0;
     }
 
-    // The CPU time is the total time taken by all thread. If we used that as
-    // the denominator, we'd be calculating the rate per thread here. This is
-    // why we have to divide the total cpu_time by the number of threads for
-    // global counters to get a global rate.
-    const double thread_seconds = seconds / b.threads();
-    internal::Finish(&report.counters, results.iterations, thread_seconds,
+    internal::Finish(&report.counters, results.iterations, seconds,
                      b.threads());
   }
   return report;
@@ -361,6 +356,9 @@ BenchmarkRunner::IterationResults BenchmarkRunner::DoNIterations() {
   } else if (b.use_real_time()) {
     i.seconds = i.results.real_time_used;
   }
+  // The time is the sum over all threads, we want each of them to run the
+  // specificed minimum time.
+  i.seconds /= b.threads();
 
   return i;
 }