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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![expect(
clippy::significant_drop_tightening,
reason = "Inherent in codspeed criterion_group! macro."
)]
use std::{
hint::black_box,
time::{Duration, Instant},
};
use criterion::{BatchSize, Criterion, criterion_group, criterion_main};
use neqo_transport::Pacer;
const RTT: Duration = Duration::from_millis(50);
const MTU: usize = 1_350;
const CWND: usize = MTU * 100;
/// PRIMARY: `spend()` when pacing is enabled and each call is credit-limited.
/// This is the dominant case during a paced bulk transfer: the pacer has just
/// enough credit for each packet and the call does the full division.
///
/// For pacing to actually limit, the inter-packet interval
/// `RTT * MTU / (CWND * 2)` must exceed GRANULARITY (1 ms).
/// With RTT=50ms, MTU=1350: CWND must be ≤ 33 750 bytes.
/// CWND_LIMITED=MTU*10=13 500 gives a 2.5ms inter-packet interval.
fn pacer_spend_pacing_limited(c: &mut Criterion) {
const CWND_LIMITED: usize = MTU * 10;
c.bench_function("Pacer::spend pacing-limited", |b| {
b.iter_batched(
|| {
let now = Instant::now();
// Pacer starts with one packet of credit; after the first
// spend() call it reaches zero credit and subsequent calls
// exercise the pacing-limited path (full division + wait
// interval computation).
Pacer::new(true, now, MTU, MTU)
},
|mut p| {
let now = Instant::now();
for _ in 0..1_000 {
black_box(p.spend(now, RTT, CWND_LIMITED, MTU));
}
black_box(p)
},
BatchSize::SmallInput,
);
});
}
/// `next()` fast path: credit is available, function returns `self.t`
/// without computing a division.
fn pacer_next_fast_path(c: &mut Criterion) {
c.bench_function("Pacer::next fast-path", |b| {
b.iter_batched(
|| {
let now = Instant::now();
// Full credit: next() will return immediately.
Pacer::new(true, now, CWND, MTU)
},
|p| {
for _ in 0..1_000 {
black_box(p.next(RTT, CWND));
}
black_box(p)
},
BatchSize::SmallInput,
);
});
}
/// `spend()` when pacing is disabled: the function must still update
/// `self.t` but should return `false` immediately without any arithmetic.
fn pacer_spend_disabled(c: &mut Criterion) {
c.bench_function("Pacer::spend disabled", |b| {
b.iter_batched(
|| {
let now = Instant::now();
Pacer::new(false, now, CWND, MTU)
},
|mut p| {
let now = Instant::now();
for _ in 0..1_000 {
black_box(p.spend(now, RTT, CWND, MTU));
}
black_box(p)
},
BatchSize::SmallInput,
);
});
}
criterion_group!(
benches,
pacer_spend_pacing_limited,
pacer_next_fast_path,
pacer_spend_disabled,
);
criterion_main!(benches);