quiche/recovery/
rtt.rs

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26
27use std::time::Duration;
28use std::time::Instant;
29
30use crate::minmax::Minmax;
31use crate::recovery::GRANULARITY;
32
33pub(crate) const INITIAL_RTT: Duration = Duration::from_millis(333);
34
35pub(crate) const RTT_WINDOW: Duration = Duration::from_secs(300);
36
37pub struct RttStats {
38    pub(super) latest_rtt: Duration,
39
40    pub(super) smoothed_rtt: Duration,
41
42    pub(super) rttvar: Duration,
43
44    pub(super) min_rtt: Minmax<Duration>,
45
46    pub(super) max_ack_delay: Duration,
47
48    pub(super) first_rtt_sample: Option<Instant>,
49}
50
51impl std::fmt::Debug for RttStats {
52    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
53        f.debug_struct("RttStats")
54            .field("lastest_rtt", &self.latest_rtt)
55            .field("srtt", &self.smoothed_rtt)
56            .field("minrtt", &*self.min_rtt)
57            .field("rttvar", &self.rttvar)
58            .finish()
59    }
60}
61
62impl RttStats {
63    pub(crate) fn new(max_ack_delay: Duration) -> Self {
64        RttStats {
65            latest_rtt: Duration::ZERO,
66            min_rtt: Minmax::new(INITIAL_RTT),
67            smoothed_rtt: INITIAL_RTT,
68            rttvar: INITIAL_RTT / 2,
69            first_rtt_sample: None,
70            max_ack_delay,
71        }
72    }
73
74    pub(crate) fn update_rtt(
75        &mut self, latest_rtt: Duration, mut ack_delay: Duration, now: Instant,
76        handshake_confirmed: bool,
77    ) {
78        self.latest_rtt = latest_rtt;
79
80        if self.first_rtt_sample.is_none() {
81            self.min_rtt.reset(now, latest_rtt);
82            self.smoothed_rtt = latest_rtt;
83            self.rttvar = latest_rtt / 2;
84            self.first_rtt_sample = Some(now);
85            return;
86        }
87
88        // min_rtt ignores acknowledgment delay.
89        self.min_rtt.running_min(RTT_WINDOW, now, latest_rtt);
90
91        // Limit ack_delay by max_ack_delay after handshake confirmation.
92        if handshake_confirmed {
93            ack_delay = ack_delay.min(self.max_ack_delay);
94        }
95
96        // Adjust for acknowledgment delay if plausible.
97        let mut adjusted_rtt = latest_rtt;
98        if latest_rtt >= *self.min_rtt + ack_delay {
99            adjusted_rtt = latest_rtt - ack_delay;
100        }
101
102        self.rttvar = self.rttvar * 3 / 4 +
103            Duration::from_nanos(
104                self.smoothed_rtt
105                    .as_nanos()
106                    .abs_diff(adjusted_rtt.as_nanos()) as u64 /
107                    4,
108            );
109
110        self.smoothed_rtt = self.smoothed_rtt * 7 / 8 + adjusted_rtt / 8;
111    }
112
113    pub(crate) fn rtt(&self) -> Duration {
114        self.smoothed_rtt
115    }
116
117    #[allow(dead_code)]
118    pub(crate) fn latest_rtt(&self) -> Duration {
119        self.latest_rtt
120    }
121
122    pub(crate) fn rttvar(&self) -> Duration {
123        self.rttvar
124    }
125
126    pub(crate) fn min_rtt(&self) -> Option<Duration> {
127        self.min_rtt.ne(&Duration::ZERO).then_some(*self.min_rtt)
128    }
129
130    pub(crate) fn loss_delay(&self, time_thresh: f64) -> Duration {
131        self.latest_rtt
132            .max(self.smoothed_rtt)
133            .mul_f64(time_thresh)
134            .max(GRANULARITY)
135    }
136}
quiche/recovery/rtt.rs

quiche/recovery/
rtt.rs
