quiche/recovery/congestion/bbr2/
per_loss.rs

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26
27use super::*;
28
29// BBR2 Functions on every packet loss event.
30//
31// 4.2.4.  Per-Loss Steps
32pub fn bbr2_update_on_loss(
33    r: &mut Congestion, packet: &Sent, lost_bytes: usize, now: Instant,
34) {
35    bbr2_handle_lost_packet(r, packet, lost_bytes, now);
36}
37
38// 4.5.6.  Updating the Model Upon Packet Loss
39// 4.5.6.2.  Probing for Bandwidth In ProbeBW
40pub fn bbr2_check_inflight_too_high(r: &mut Congestion, now: Instant) -> bool {
41    if bbr2_is_inflight_too_high(r) {
42        if r.bbr2_state.bw_probe_samples {
43            bbr2_handle_inflight_too_high(r, now);
44        }
45
46        // inflight too high.
47        return true;
48    }
49
50    // inflight not too high.
51    false
52}
53
54pub fn bbr2_is_inflight_too_high(r: &mut Congestion) -> bool {
55    r.bbr2_state.lost > (r.bbr2_state.tx_in_flight as f64 * LOSS_THRESH) as usize
56}
57
58fn bbr2_handle_inflight_too_high(r: &mut Congestion, now: Instant) {
59    // Only react once per bw probe.
60    r.bbr2_state.bw_probe_samples = false;
61
62    if !r.delivery_rate.sample_is_app_limited() {
63        r.bbr2_state.inflight_hi = r
64            .bbr2_state
65            .tx_in_flight
66            .max((per_ack::bbr2_target_inflight(r) as f64 * BETA) as usize);
67    }
68
69    if r.bbr2_state.state == BBR2StateMachine::ProbeBWUP {
70        per_ack::bbr2_start_probe_bw_down(r, now);
71    }
72}
73
74fn bbr2_handle_lost_packet(
75    r: &mut Congestion, packet: &Sent, lost_bytes: usize, now: Instant,
76) {
77    if !r.bbr2_state.bw_probe_samples {
78        return;
79    }
80
81    r.bbr2_state.tx_in_flight = packet.tx_in_flight;
82    r.bbr2_state.lost = lost_bytes;
83
84    r.delivery_rate.update_app_limited(packet.is_app_limited);
85
86    if bbr2_is_inflight_too_high(r) {
87        r.bbr2_state.tx_in_flight = bbr2_inflight_hi_from_lost_packet(r, packet);
88
89        bbr2_handle_inflight_too_high(r, now);
90    }
91}
92
93fn bbr2_inflight_hi_from_lost_packet(r: &mut Congestion, packet: &Sent) -> usize {
94    let size = packet.size;
95    let inflight_prev = r.bbr2_state.tx_in_flight - size;
96    let lost_prev = r.bbr2_state.lost - size;
97    let lost_prefix = (LOSS_THRESH * inflight_prev as f64 - lost_prev as f64) /
98        (1.0 - LOSS_THRESH);
99
100    inflight_prev + lost_prefix as usize
101}
102
103// 4.5.6.3.  When not Probing for Bandwidth
104pub fn bbr2_update_latest_delivery_signals(r: &mut Congestion) {
105    let bbr = &mut r.bbr2_state;
106
107    // Near start of ACK processing.
108    bbr.loss_round_start = false;
109    bbr.bw_latest = bbr.bw_latest.max(r.delivery_rate.sample_delivery_rate());
110    bbr.inflight_latest =
111        bbr.inflight_latest.max(r.delivery_rate.sample_delivered());
112
113    if r.delivery_rate.sample_prior_delivered() >= bbr.loss_round_delivered {
114        bbr.loss_round_delivered = r.delivery_rate.delivered();
115        bbr.loss_round_start = true;
116    }
117}
118
119pub fn bbr2_advance_latest_delivery_signals(r: &mut Congestion) {
120    let bbr = &mut r.bbr2_state;
121
122    // Near end of ACK processing.
123    if bbr.loss_round_start {
124        bbr.bw_latest = r.delivery_rate.sample_delivery_rate();
125        bbr.inflight_latest = r.delivery_rate.sample_delivered();
126    }
127}
128
129pub fn bbr2_reset_congestion_signals(r: &mut Congestion) {
130    let bbr = &mut r.bbr2_state;
131
132    bbr.loss_in_round = false;
133    bbr.loss_events_in_round = 0;
134    bbr.bw_latest = 0;
135    bbr.inflight_latest = 0;
136}
137
138pub fn bbr2_update_congestion_signals(r: &mut Congestion, packet: &Acked) {
139    // Update congestion state on every ACK.
140    per_ack::bbr2_update_max_bw(r, packet);
141
142    if r.bbr2_state.lost > 0 {
143        r.bbr2_state.loss_in_round = true;
144        r.bbr2_state.loss_events_in_round += 1;
145    }
146
147    if !r.bbr2_state.loss_round_start {
148        // Wait until end of round trip.
149        return;
150    }
151
152    bbr2_adapt_lower_bounds_from_congestion(r);
153
154    r.bbr2_state.loss_in_round = false;
155    r.bbr2_state.loss_events_in_round = 0;
156}
157
158fn bbr2_adapt_lower_bounds_from_congestion(r: &mut Congestion) {
159    // Once per round-trip respond to congestion.
160    if bbr2_is_probing_bw(r) {
161        return;
162    }
163
164    if r.bbr2_state.loss_in_round {
165        bbr2_init_lower_bounds(r);
166        bbr2_loss_lower_bounds(r);
167    }
168}
169
170fn bbr2_init_lower_bounds(r: &mut Congestion) {
171    let bbr = &mut r.bbr2_state;
172
173    // Handle the first congestion episode in this cycle.
174    if bbr.bw_lo == u64::MAX {
175        bbr.bw_lo = bbr.max_bw;
176    }
177
178    if bbr.inflight_lo == usize::MAX {
179        bbr.inflight_lo = r.congestion_window;
180    }
181}
182
183fn bbr2_loss_lower_bounds(r: &mut Congestion) {
184    let bbr = &mut r.bbr2_state;
185
186    // Adjust model once per round based on loss.
187    bbr.bw_lo = bbr.bw_latest.max((bbr.bw_lo as f64 * BETA) as u64);
188    bbr.inflight_lo = bbr
189        .inflight_latest
190        .max((bbr.inflight_lo as f64 * BETA) as usize);
191}
192
193pub fn bbr2_reset_lower_bounds(r: &mut Congestion) {
194    let bbr = &mut r.bbr2_state;
195
196    bbr.bw_lo = u64::MAX;
197    bbr.inflight_lo = usize::MAX;
198}
199
200pub fn bbr2_bound_bw_for_model(r: &mut Congestion) {
201    let bbr = &mut r.bbr2_state;
202
203    bbr.bw = bbr.max_bw.min(bbr.bw_lo.min(bbr.bw_hi));
204}
205
206// This function is not defined in the draft but used.
207fn bbr2_is_probing_bw(r: &mut Congestion) -> bool {
208    let state = r.bbr2_state.state;
209
210    state == BBR2StateMachine::Startup ||
211        state == BBR2StateMachine::ProbeBWREFILL ||
212        state == BBR2StateMachine::ProbeBWUP
213}
quiche/recovery/congestion/bbr2/per_loss.rs

quiche/recovery/congestion/bbr2/
per_loss.rs
