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Diffstat (limited to 'third_party/rust/neqo-transport/src/cc/tests/cubic.rs')
-rw-r--r-- | third_party/rust/neqo-transport/src/cc/tests/cubic.rs | 333 |
1 files changed, 333 insertions, 0 deletions
diff --git a/third_party/rust/neqo-transport/src/cc/tests/cubic.rs b/third_party/rust/neqo-transport/src/cc/tests/cubic.rs new file mode 100644 index 0000000000..0c82e47817 --- /dev/null +++ b/third_party/rust/neqo-transport/src/cc/tests/cubic.rs @@ -0,0 +1,333 @@ +// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +#![allow(clippy::cast_possible_truncation)] +#![allow(clippy::cast_sign_loss)] + +use std::{ + convert::TryFrom, + ops::Sub, + time::{Duration, Instant}, +}; + +use test_fixture::now; + +use crate::{ + cc::{ + classic_cc::{ClassicCongestionControl, CWND_INITIAL}, + cubic::{ + Cubic, CUBIC_ALPHA, CUBIC_BETA_USIZE_DIVIDEND, CUBIC_BETA_USIZE_DIVISOR, CUBIC_C, + CUBIC_FAST_CONVERGENCE, + }, + CongestionControl, MAX_DATAGRAM_SIZE, MAX_DATAGRAM_SIZE_F64, + }, + packet::PacketType, + rtt::RttEstimate, + tracking::SentPacket, +}; + +const RTT: Duration = Duration::from_millis(100); +const RTT_ESTIMATE: RttEstimate = RttEstimate::from_duration(Duration::from_millis(100)); +const CWND_INITIAL_F64: f64 = 10.0 * MAX_DATAGRAM_SIZE_F64; +const CWND_INITIAL_10_F64: f64 = 10.0 * CWND_INITIAL_F64; +const CWND_INITIAL_10: usize = 10 * CWND_INITIAL; +const CWND_AFTER_LOSS: usize = CWND_INITIAL * CUBIC_BETA_USIZE_DIVIDEND / CUBIC_BETA_USIZE_DIVISOR; +const CWND_AFTER_LOSS_SLOW_START: usize = + (CWND_INITIAL + MAX_DATAGRAM_SIZE) * CUBIC_BETA_USIZE_DIVIDEND / CUBIC_BETA_USIZE_DIVISOR; + +fn fill_cwnd(cc: &mut ClassicCongestionControl<Cubic>, mut next_pn: u64, now: Instant) -> u64 { + while cc.bytes_in_flight() < cc.cwnd() { + let sent = SentPacket::new( + PacketType::Short, + next_pn, // pn + now, // time sent + true, // ack eliciting + Vec::new(), // tokens + MAX_DATAGRAM_SIZE, // size + ); + cc.on_packet_sent(&sent); + next_pn += 1; + } + next_pn +} + +fn ack_packet(cc: &mut ClassicCongestionControl<Cubic>, pn: u64, now: Instant) { + let acked = SentPacket::new( + PacketType::Short, + pn, // pn + now, // time sent + true, // ack eliciting + Vec::new(), // tokens + MAX_DATAGRAM_SIZE, // size + ); + cc.on_packets_acked(&[acked], &RTT_ESTIMATE, now); +} + +fn packet_lost(cc: &mut ClassicCongestionControl<Cubic>, pn: u64) { + const PTO: Duration = Duration::from_millis(120); + let p_lost = SentPacket::new( + PacketType::Short, + pn, // pn + now(), // time sent + true, // ack eliciting + Vec::new(), // tokens + MAX_DATAGRAM_SIZE, // size + ); + cc.on_packets_lost(None, None, PTO, &[p_lost]); +} + +fn expected_tcp_acks(cwnd_rtt_start: usize) -> u64 { + (f64::from(i32::try_from(cwnd_rtt_start).unwrap()) / MAX_DATAGRAM_SIZE_F64 / CUBIC_ALPHA) + .round() as u64 +} + +#[test] +fn tcp_phase() { + let mut cubic = ClassicCongestionControl::new(Cubic::default()); + + // change to congestion avoidance state. + cubic.set_ssthresh(1); + + let mut now = now(); + let start_time = now; + // helper variables to remember the next packet number to be sent/acked. + let mut next_pn_send = 0; + let mut next_pn_ack = 0; + + next_pn_send = fill_cwnd(&mut cubic, next_pn_send, now); + + // This will start with TCP phase. + // in this phase cwnd is increase by CUBIC_ALPHA every RTT. We can look at it as + // increase of MAX_DATAGRAM_SIZE every 1 / CUBIC_ALPHA RTTs. + // The phase will end when cwnd calculated with cubic equation is equal to TCP estimate: + // CUBIC_C * (n * RTT / CUBIC_ALPHA)^3 * MAX_DATAGRAM_SIZE = n * MAX_DATAGRAM_SIZE + // from this n = sqrt(CUBIC_ALPHA^3/ (CUBIC_C * RTT^3)). + let num_tcp_increases = (CUBIC_ALPHA.powi(3) / (CUBIC_C * RTT.as_secs_f64().powi(3))) + .sqrt() + .floor() as u64; + + for _ in 0..num_tcp_increases { + let cwnd_rtt_start = cubic.cwnd(); + // Expected acks during a period of RTT / CUBIC_ALPHA. + let acks = expected_tcp_acks(cwnd_rtt_start); + // The time between acks if they are ideally paced over a RTT. + let time_increase = RTT / u32::try_from(cwnd_rtt_start / MAX_DATAGRAM_SIZE).unwrap(); + + for _ in 0..acks { + now += time_increase; + ack_packet(&mut cubic, next_pn_ack, now); + next_pn_ack += 1; + next_pn_send = fill_cwnd(&mut cubic, next_pn_send, now); + } + + assert_eq!(cubic.cwnd() - cwnd_rtt_start, MAX_DATAGRAM_SIZE); + } + + // The next increase will be according to the cubic equation. + + let cwnd_rtt_start = cubic.cwnd(); + // cwnd_rtt_start has change, therefore calculate new time_increase (the time + // between acks if they are ideally paced over a RTT). + let time_increase = RTT / u32::try_from(cwnd_rtt_start / MAX_DATAGRAM_SIZE).unwrap(); + let mut num_acks = 0; // count the number of acks. until cwnd is increased by MAX_DATAGRAM_SIZE. + + while cwnd_rtt_start == cubic.cwnd() { + num_acks += 1; + now += time_increase; + ack_packet(&mut cubic, next_pn_ack, now); + next_pn_ack += 1; + next_pn_send = fill_cwnd(&mut cubic, next_pn_send, now); + } + + // Make sure that the increase is not according to TCP equation, i.e., that it took + // less than RTT / CUBIC_ALPHA. + let expected_ack_tcp_increase = expected_tcp_acks(cwnd_rtt_start); + assert!(num_acks < expected_ack_tcp_increase); + + // This first increase after a TCP phase may be shorter than what it would take by a regular + // cubic phase, because of the proper byte counting and the credit it already had before + // entering this phase. Therefore We will perform another round and compare it to expected + // increase using the cubic equation. + + let cwnd_rtt_start_after_tcp = cubic.cwnd(); + let elapsed_time = now - start_time; + + // calculate new time_increase. + let time_increase = RTT / u32::try_from(cwnd_rtt_start_after_tcp / MAX_DATAGRAM_SIZE).unwrap(); + let mut num_acks2 = 0; // count the number of acks. until cwnd is increased by MAX_DATAGRAM_SIZE. + + while cwnd_rtt_start_after_tcp == cubic.cwnd() { + num_acks2 += 1; + now += time_increase; + ack_packet(&mut cubic, next_pn_ack, now); + next_pn_ack += 1; + next_pn_send = fill_cwnd(&mut cubic, next_pn_send, now); + } + + let expected_ack_tcp_increase2 = expected_tcp_acks(cwnd_rtt_start_after_tcp); + assert!(num_acks2 < expected_ack_tcp_increase2); + + // The time needed to increase cwnd by MAX_DATAGRAM_SIZE using the cubic equation will be + // calculates from: W_cubic(elapsed_time + t_to_increase) - W_cubis(elapsed_time) = + // MAX_DATAGRAM_SIZE => CUBIC_C * (elapsed_time + t_to_increase)^3 * MAX_DATAGRAM_SIZE + + // CWND_INITIAL - CUBIC_C * elapsed_time^3 * MAX_DATAGRAM_SIZE + CWND_INITIAL = + // MAX_DATAGRAM_SIZE => t_to_increase = cbrt((1 + CUBIC_C * elapsed_time^3) / CUBIC_C) - + // elapsed_time (t_to_increase is in seconds) + // number of ack needed is t_to_increase / time_increase. + let expected_ack_cubic_increase = + ((((1.0 + CUBIC_C * (elapsed_time).as_secs_f64().powi(3)) / CUBIC_C).cbrt() + - elapsed_time.as_secs_f64()) + / time_increase.as_secs_f64()) + .ceil() as u64; + // num_acks is very close to the calculated value. The exact value is hard to calculate + // because the proportional increase(i.e. curr_cwnd_f64 / (target - curr_cwnd_f64) * + // MAX_DATAGRAM_SIZE_F64) and the byte counting. + assert_eq!(num_acks2, expected_ack_cubic_increase + 2); +} + +#[test] +fn cubic_phase() { + let mut cubic = ClassicCongestionControl::new(Cubic::default()); + // Set last_max_cwnd to a higher number make sure that cc is the cubic phase (cwnd is calculated + // by the cubic equation). + cubic.set_last_max_cwnd(CWND_INITIAL_10_F64); + // Set ssthresh to something small to make sure that cc is in the congection avoidance phase. + cubic.set_ssthresh(1); + let mut now = now(); + let mut next_pn_send = 0; + let mut next_pn_ack = 0; + + next_pn_send = fill_cwnd(&mut cubic, next_pn_send, now); + + let k = ((CWND_INITIAL_10_F64 - CWND_INITIAL_F64) / CUBIC_C / MAX_DATAGRAM_SIZE_F64).cbrt(); + let epoch_start = now; + + // The number of RTT until W_max is reached. + let num_rtts_w_max = (k / RTT.as_secs_f64()).round() as u64; + for _ in 0..num_rtts_w_max { + let cwnd_rtt_start = cubic.cwnd(); + // Expected acks + let acks = cwnd_rtt_start / MAX_DATAGRAM_SIZE; + let time_increase = RTT / u32::try_from(acks).unwrap(); + for _ in 0..acks { + now += time_increase; + ack_packet(&mut cubic, next_pn_ack, now); + next_pn_ack += 1; + next_pn_send = fill_cwnd(&mut cubic, next_pn_send, now); + } + + let expected = + (CUBIC_C * ((now - epoch_start).as_secs_f64() - k).powi(3) * MAX_DATAGRAM_SIZE_F64 + + CWND_INITIAL_10_F64) + .round() as usize; + + assert_within(cubic.cwnd(), expected, MAX_DATAGRAM_SIZE); + } + assert_eq!(cubic.cwnd(), CWND_INITIAL_10); +} + +fn assert_within<T: Sub<Output = T> + PartialOrd + Copy>(value: T, expected: T, margin: T) { + if value >= expected { + assert!(value - expected < margin); + } else { + assert!(expected - value < margin); + } +} + +#[test] +fn congestion_event_slow_start() { + let mut cubic = ClassicCongestionControl::new(Cubic::default()); + + _ = fill_cwnd(&mut cubic, 0, now()); + ack_packet(&mut cubic, 0, now()); + + assert_within(cubic.last_max_cwnd(), 0.0, f64::EPSILON); + + // cwnd is increased by 1 in slow start phase, after an ack. + assert_eq!(cubic.cwnd(), CWND_INITIAL + MAX_DATAGRAM_SIZE); + + // Trigger a congestion_event in slow start phase + packet_lost(&mut cubic, 1); + + // last_max_cwnd is equal to cwnd before decrease. + assert_within( + cubic.last_max_cwnd(), + CWND_INITIAL_F64 + MAX_DATAGRAM_SIZE_F64, + f64::EPSILON, + ); + assert_eq!(cubic.cwnd(), CWND_AFTER_LOSS_SLOW_START); +} + +#[test] +fn congestion_event_congestion_avoidance() { + let mut cubic = ClassicCongestionControl::new(Cubic::default()); + + // Set ssthresh to something small to make sure that cc is in the congection avoidance phase. + cubic.set_ssthresh(1); + + // Set last_max_cwnd to something smaller than cwnd so that the fast convergence is not + // triggered. + cubic.set_last_max_cwnd(3.0 * MAX_DATAGRAM_SIZE_F64); + + _ = fill_cwnd(&mut cubic, 0, now()); + ack_packet(&mut cubic, 0, now()); + + assert_eq!(cubic.cwnd(), CWND_INITIAL); + + // Trigger a congestion_event in slow start phase + packet_lost(&mut cubic, 1); + + assert_within(cubic.last_max_cwnd(), CWND_INITIAL_F64, f64::EPSILON); + assert_eq!(cubic.cwnd(), CWND_AFTER_LOSS); +} + +#[test] +fn congestion_event_congestion_avoidance_2() { + let mut cubic = ClassicCongestionControl::new(Cubic::default()); + + // Set ssthresh to something small to make sure that cc is in the congection avoidance phase. + cubic.set_ssthresh(1); + + // Set last_max_cwnd to something higher than cwnd so that the fast convergence is triggered. + cubic.set_last_max_cwnd(CWND_INITIAL_10_F64); + + _ = fill_cwnd(&mut cubic, 0, now()); + ack_packet(&mut cubic, 0, now()); + + assert_within(cubic.last_max_cwnd(), CWND_INITIAL_10_F64, f64::EPSILON); + assert_eq!(cubic.cwnd(), CWND_INITIAL); + + // Trigger a congestion_event. + packet_lost(&mut cubic, 1); + + assert_within( + cubic.last_max_cwnd(), + CWND_INITIAL_F64 * CUBIC_FAST_CONVERGENCE, + f64::EPSILON, + ); + assert_eq!(cubic.cwnd(), CWND_AFTER_LOSS); +} + +#[test] +fn congestion_event_congestion_avoidance_test_no_overflow() { + const PTO: Duration = Duration::from_millis(120); + let mut cubic = ClassicCongestionControl::new(Cubic::default()); + + // Set ssthresh to something small to make sure that cc is in the congection avoidance phase. + cubic.set_ssthresh(1); + + // Set last_max_cwnd to something higher than cwnd so that the fast convergence is triggered. + cubic.set_last_max_cwnd(CWND_INITIAL_10_F64); + + _ = fill_cwnd(&mut cubic, 0, now()); + ack_packet(&mut cubic, 1, now()); + + assert_within(cubic.last_max_cwnd(), CWND_INITIAL_10_F64, f64::EPSILON); + assert_eq!(cubic.cwnd(), CWND_INITIAL); + + // Now ack packet that was send earlier. + ack_packet(&mut cubic, 0, now().checked_sub(PTO).unwrap()); +} |