[BUG] --benchmark_min_time flag not working as intended #1663
Description
Consider the following example:
test.cc:
#include <benchmark/benchmark.h>
static void BM_Test(benchmark::State& state) {
int i = 0;
for (auto _ : state) {
benchmark::DoNotOptimize(i++);
}
}
BENCHMARK(BM_Test);
BENCHMARK_MAIN();
$ g++ test.cc -std=c++11 -isystem include -Lbuild/src -lbenchmark -lpthread -o test_b
$ time ./test_b --benchmark_min_time=30s
2023-09-15T14:58:41+02:00
Running ./test_b
Run on (128 X 4027.19 MHz CPU s)
CPU Caches:
L1 Data 32 KiB (x64)
L1 Instruction 32 KiB (x64)
L2 Unified 512 KiB (x64)
L3 Unified 16384 KiB (x16)
Load Average: 0.90, 0.85, 0.75
--------------------------------------------------------
Benchmark Time CPU Iterations
--------------------------------------------------------
BM_Test 2.03 ns 2.03 ns 1000000000
real 0m2.274s
user 0m2.259s
sys 0m0.016s
Expected behavior
The benchmark runs for at least 30s.
Actual behavior
The benchmark runs for only a little more than 2s.
Additional context
The reason why the benchmark stops early is the hard-coded limit of 1,000,000,000 iterations in benchmark_runner.cc. However, 1,000,000,000 iterations can be reached relatively quickly on recent machines (if KeepRunningBatch() is used it can be reached even faster than in the example above).