ERROR: At least one measurement of benchmark {} took zero time per iteration. #862
Description
I was getting this error when benchmarking my code, so I boiled it down to a minimal project that reproduces the same error message. The key seems to be if the setup function (for iter_batched) takes a long time, but the routine itself takes little time, then I get this error message. The following code generates the error message on my machine (CPU: Apple M4 Max) but if I reduce the SETUP const from 1_000_000 to 100_000 then the error message stops appearing.
use criterion::{criterion_group, criterion_main, Criterion, BatchSize};
use std::hint::black_box;
const SETUP: i32 = 1_000_000;
fn test_criterion(c: &mut Criterion) {
let setup = || {
let mut i = 0;
let mut x = 1;
while i < SETUP {
x += black_box(i * x);
i += 1;
}
black_box(i)
};
let f = |i| {
let mut j = 0;
let mut x = 1;
while j < 2 {
x += black_box(i * x + j);
j += black_box(1);
}
};
c.bench_function("test_criterion", move |b| b.iter_batched(setup, f, BatchSize::SmallInput));
}
criterion_group!(
benches,
test_criterion,
);
criterion_main!(benches);