[libc] Add Minimum Time and Iterations, Reduce Epsilon (#100838)

This PR adds minimums (50 iterations, 500 us, and epsilon of 0.0001) to
ensure that all benchmarks run at least a set number of times before
outputting a final measurement.

Author: jameshu15869

libc/benchmarks/gpu/LibcGpuBenchmark.cpp

@@ -205,6 +205,7 @@ BenchmarkResult benchmark(const BenchmarkOptions &options,
     if (samples >= options.max_samples || iterations >= options.max_iterations)
       break;
     if (total_time >= options.min_duration && samples >= options.min_samples &&
+        total_iterations >= options.min_iterations &&
         change_ratio < options.epsilon)
       break;
 

libc/benchmarks/gpu/LibcGpuBenchmark.h

@@ -17,12 +17,13 @@ namespace benchmarks {
 
 struct BenchmarkOptions {
   uint32_t initial_iterations = 1;
+  uint32_t min_iterations = 50;
   uint32_t max_iterations = 10000000;
   uint32_t min_samples = 4;
   uint32_t max_samples = 1000;
-  int64_t min_duration = 0;                  // in nanoseconds (ns)
+  int64_t min_duration = 500 * 1000;         // 500 * 1000 nanoseconds = 500 us
   int64_t max_duration = 1000 * 1000 * 1000; // 1e9 nanoseconds = 1 second
-  double epsilon = 0.01;
+  double epsilon = 0.0001;
   double scaling_factor = 1.4;
 };