quiche/recovery/gcongestion/bbr2/
startup.rs

1// Copyright (c) 2015 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// Copyright (C) 2023, Cloudflare, Inc.
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9// modification, are permitted provided that the following conditions are
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12//     * Redistributions of source code must retain the above copyright notice,
13//       this list of conditions and the following disclaimer.
14//
15//     * Redistributions in binary form must reproduce the above copyright
16//       notice, this list of conditions and the following disclaimer in the
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19// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
20// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
21// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
23// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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25// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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30
31use std::time::Instant;
32
33use super::mode::Mode;
34use super::mode::ModeImpl;
35use super::network_model::BBRv2NetworkModel;
36use super::Acked;
37use super::BBRv2CongestionEvent;
38use super::Limits;
39use super::Lost;
40use super::PARAMS;
41
42#[derive(Debug)]
43pub(super) struct Startup {
44    pub(super) model: BBRv2NetworkModel,
45}
46
47impl ModeImpl for Startup {
48    fn is_probing_for_bandwidth(&self) -> bool {
49        true
50    }
51
52    fn on_congestion_event(
53        mut self, _prior_in_flight: usize, event_time: std::time::Instant,
54        _acked_packets: &[Acked], _lost_packets: &[Lost],
55        congestion_event: &mut BBRv2CongestionEvent,
56        _target_bytes_inflight: usize,
57    ) -> Mode {
58        if self.model.full_bandwidth_reached() {
59            return self.into_drain(event_time, Some(congestion_event));
60        }
61
62        if !congestion_event.end_of_round_trip {
63            return Mode::Startup(self);
64        }
65
66        let has_bandwidth_growth =
67            self.model.has_bandwidth_growth(congestion_event);
68
69        #[allow(clippy::absurd_extreme_comparisons)]
70        if PARAMS.max_startup_queue_rounds > 0 && !has_bandwidth_growth {
71            // 1.75 is less than the 2x CWND gain, but substantially more than
72            // 1.25x, the minimum bandwidth increase expected during
73            // STARTUP.
74            self.model.check_persistent_queue(1.75);
75        }
76        // TCP BBR always exits upon excessive losses. QUIC BBRv1 does not exit
77        // upon excessive losses, if enough bandwidth growth is observed or if the
78        // sample was app limited.
79        if !congestion_event.last_packet_send_state.is_app_limited &&
80            !has_bandwidth_growth
81        {
82            self.check_excessive_losses(congestion_event);
83        }
84
85        if self.model.full_bandwidth_reached() {
86            self.into_drain(event_time, Some(congestion_event))
87        } else {
88            Mode::Startup(self)
89        }
90    }
91
92    fn get_cwnd_limits(&self) -> Limits<usize> {
93        Limits {
94            lo: 0,
95            hi: self.model.inflight_lo(),
96        }
97    }
98
99    fn on_exit_quiescence(
100        self, _now: Instant, _quiescence_start_time: Instant,
101    ) -> Mode {
102        Mode::Startup(self)
103    }
104
105    fn enter(
106        &mut self, _now: Instant,
107        _congestion_event: Option<&BBRv2CongestionEvent>,
108    ) {
109        unreachable!("Enter should never be called for startup")
110    }
111
112    fn leave(
113        &mut self, _now: Instant,
114        _congestion_event: Option<&BBRv2CongestionEvent>,
115    ) {
116        // Clear bandwidth_lo if it's set during STARTUP.
117        self.model.clear_bandwidth_lo();
118    }
119}
120
121impl Startup {
122    fn into_drain(
123        mut self, now: Instant, congestion_event: Option<&BBRv2CongestionEvent>,
124    ) -> Mode {
125        self.leave(now, congestion_event);
126        let mut next_mode = Mode::drain(self.model);
127        next_mode.enter(now, congestion_event);
128        next_mode
129    }
130
131    fn check_excessive_losses(
132        &mut self, congestion_event: &mut BBRv2CongestionEvent,
133    ) {
134        if self.model.full_bandwidth_reached() {
135            return;
136        }
137
138        // At the end of a round trip. Check if loss is too high in this round.
139        if self.model.is_inflight_too_high(
140            congestion_event,
141            PARAMS.startup_full_loss_count,
142        ) {
143            let mut new_inflight_hi = self.model.bdp0();
144
145            if PARAMS.startup_loss_exit_use_max_delivered_for_inflight_hi {
146                new_inflight_hi = new_inflight_hi
147                    .max(self.model.max_bytes_delivered_in_round());
148            }
149
150            self.model.set_inflight_hi(new_inflight_hi);
151            self.model.set_full_bandwidth_reached();
152        }
153    }
154}
quiche/recovery/gcongestion/bbr2/startup.rs

quiche/recovery/gcongestion/bbr2/
startup.rs
