[BUG] Minimum benchmark time with multiple threads

Author: hahnjoCreated Jan 30, 2026Updated Jan 30, 2026

Describe the bug https://github.com/google/benchmark/pull/1836 fixed https://github.com/google/benchmark/issues/1834 and now the reported output makes more sense. However, the minimum benchmark time doesn't seem to be respected.

System Arch Linux, GCC 15.2.1, benchmark 1.9.5-1

To reproduce Consider

cpp

#include <benchmark/benchmark.h>

static void BM_MultiThreaded(benchmark::State& state) {
  int a = 0;

  for (auto _ : state) {
    for (int i = 0; i < 1000; i++) {
      benchmark::DoNotOptimize(a++);
    }
  }
}
BENCHMARK(BM_MultiThreaded)->ThreadRange(1, 8);

BENCHMARK_MAIN();

The output is somewhat expected:

---------------------------------------------------------------------
Benchmark                           Time             CPU   Iterations
---------------------------------------------------------------------
BM_MultiThreaded/threads:1        275 ns          274 ns      2585850
BM_MultiThreaded/threads:2        273 ns          272 ns      2259184
BM_MultiThreaded/threads:4        279 ns          278 ns      2449204
BM_MultiThreaded/threads:8        308 ns          307 ns      2148808

However, notice that the number of iterations stays constant - it should increase as more threads are used to run the iterations. For example:

 $ /usr/bin/time -v ./benchmark-multithreaded --benchmark_min_time=1s --benchmark_filter=threads:8
[...]
	User time (seconds): 1.72
	Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.25

With previous versions of benchmark, this could be fixed with UseRealTime() but that doesn't seem to work anymore since (probably) https://github.com/google/benchmark/pull/1836.

Expected behavior Each benchmark should spend the minimum time (per thread).

Source: google/benchmark

View original on GitHub View discussion on GitHub