Limit maximum number of iterations in folly::Benchmark with bm_max_iters

Summary:
We are using `bm_max_iters` in folly and other part of the code in fbcode but it didn't really exist in Benchmark.cpp. For example: https://github.com/facebook/folly/blob/master/folly/test/function_benchmark/main.cpp#L29

This patch adds back this functionality.

This diff depends on D3990600.

Reviewed By: yfeldblum

Differential Revision: D3989499

fbshipit-source-id: d2303b2bebb196e84a592d54a72af68171971491

diff --git a/folly/Benchmark.cpp b/folly/Benchmark.cpp
index 370a737a873b9f07ec9be9e7ce9e1cf082d8f0c4..2b64c12bbafca2fa31cd0837b4e5c994fcbef333 100644 (file)
--- a/folly/Benchmark.cpp
+++ b/folly/Benchmark.cpp
@@ -50,6 +50,11 @@ DEFINE_int64(
     1,
     "Minimum # of iterations we'll try for each benchmark.");
 
+DEFINE_int64(
+    bm_max_iters,
+    1L << 30L,
+    "Maximum # of iterations we'll try for each benchmark.");
+
 DEFINE_int32(
     bm_max_secs,
     1,
@@ -262,7 +267,8 @@ static double runBenchmarkGetNSPerIteration(const BenchmarkFun& fun,
   size_t actualEpochs = 0;
 
   for (; actualEpochs < epochs; ++actualEpochs) {
-    for (unsigned int n = FLAGS_bm_min_iters; n < (1UL << 30); n *= 2) {
+    const auto maxIters = FLAGS_bm_max_iters;
+    for (unsigned int n = FLAGS_bm_min_iters; n < maxIters; n *= 2) {
       auto const nsecsAndIter = fun(n);
       if (nsecsAndIter.first < minNanoseconds) {
         continue;