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|
//! Sync throughput with peers, measured from sync exchanges we have anyway: from sending
//! a sync message until the peer's answer arrives, the sync bytes that went either way
//! with that peer. No transfers of our own.
//!
//! Only exchanges of at least `MIN_BYTES` count; smaller ones measure the round trip,
//! not the throughput. The round trip (`swarm::rtt`) is taken off the elapsed time, but
//! never more than half of it, so a stale round trip can't inflate a sample. What
//! remains also includes the time the peer took to apply and answer: this is the rate a
//! peer delivers at in practice, not the raw capacity of the path.
//!
//! Samples are smoothed (exponential moving average, weight 1/4). Large exchanges are
//! rare (catching up, big writes), so estimates are kept however old; they come with
//! their age.
use std::collections::HashMap;
use std::time::Duration;
use tokio::time::Instant;
use crate::transport::traffic::Traffic;
/// Smallest exchange that counts: some dozens of Mycelium chunks.
const MIN_BYTES: u64 = 32 * 1024;
const WEIGHT: f64 = 0.25;
/// Sync bytes exchanged with a peer so far (from the traffic counters).
#[derive(Debug, Default, Clone, Copy)]
pub(crate) struct SyncBytes {
sent: u64,
received: u64,
}
impl SyncBytes {
pub(crate) fn of(traffic: &Traffic, peer: &str) -> Self {
traffic
.peer(peer)
.map(|t| Self {
sent: t.sent.sync.bytes,
received: t.received.sync.bytes,
})
.unwrap_or_default()
}
/// Bytes either way since `earlier` (0 if the counters were dropped meanwhile).
fn since(&self, earlier: &SyncBytes) -> u64 {
self.sent.saturating_sub(earlier.sent) + self.received.saturating_sub(earlier.received)
}
}
#[derive(Debug, Clone, Copy)]
pub(crate) struct Estimate {
pub(crate) bytes_per_sec: f64,
pub(crate) samples: u32,
/// When the last sample was taken.
pub(crate) at: Instant,
}
#[derive(Debug, Default)]
pub(crate) struct ThroughputTable {
peers: HashMap<String, Estimate>,
}
impl ThroughputTable {
/// A sync exchange with `peer` finished: it started at `started` with the counters
/// at `before`, and its answer arrived at `arrived` with the counters at `after`.
pub(crate) fn exchange(
&mut self,
peer: &str,
(started, before): (Instant, SyncBytes),
(arrived, after): (Instant, SyncBytes),
rtt: Option<Duration>,
) {
let bytes = after.since(&before);
if bytes < MIN_BYTES {
return;
}
let elapsed = arrived.saturating_duration_since(started);
let transfer = elapsed
.saturating_sub(rtt.unwrap_or_default())
.max(elapsed / 2);
if transfer.is_zero() {
return;
}
let sample = bytes as f64 / transfer.as_secs_f64();
let estimate = self.peers.entry(peer.to_owned()).or_insert(Estimate {
bytes_per_sec: sample,
samples: 0,
at: arrived,
});
if estimate.samples > 0 {
estimate.bytes_per_sec += WEIGHT * (sample - estimate.bytes_per_sec);
}
estimate.samples += 1;
estimate.at = arrived;
}
pub(crate) fn get(&self, peer: &str) -> Option<Estimate> {
self.peers.get(peer).copied()
}
pub(crate) fn retain(&mut self, mut keep: impl FnMut(&str) -> bool) {
self.peers.retain(|peer, _| keep(peer));
}
}
#[cfg(test)]
mod tests {
use super::*;
fn bytes(sent: u64, received: u64) -> SyncBytes {
SyncBytes { sent, received }
}
#[test]
fn small_exchanges_dont_count() {
let mut table = ThroughputTable::default();
let t0 = Instant::now();
table.exchange(
"a",
(t0, bytes(0, 0)),
(t0 + Duration::from_millis(200), bytes(500, 10_000)),
None,
);
assert!(table.get("a").is_none());
}
#[test]
fn round_trip_is_taken_off_but_at_most_half() {
let mut table = ThroughputTable::default();
let t0 = Instant::now();
// 1 MB in 2 s, of which 1 s round trip: 1 MB/s.
table.exchange(
"a",
(t0, bytes(100, 0)),
(t0 + Duration::from_secs(2), bytes(200, 999_900)),
Some(Duration::from_secs(1)),
);
let a = table.get("a").unwrap();
assert!((a.bytes_per_sec - 1_000_000.0).abs() < 1.0);
// A round trip longer than the exchange takes off only half.
table.exchange(
"b",
(t0, bytes(0, 0)),
(t0 + Duration::from_secs(2), bytes(0, 1_000_000)),
Some(Duration::from_secs(5)),
);
assert!((table.get("b").unwrap().bytes_per_sec - 1_000_000.0).abs() < 1.0);
}
#[test]
fn smoothed() {
let mut table = ThroughputTable::default();
let t0 = Instant::now();
for received in [500_000u64, 1_000_000] {
table.exchange(
"a",
(t0, bytes(0, 0)),
(t0 + Duration::from_secs(1), bytes(0, received)),
None,
);
}
// Samples of 500 kB/s, then 1 MB/s: 500 kB/s + (1 MB/s - 500 kB/s) / 4.
let a = table.get("a").unwrap();
assert_eq!(a.samples, 2);
assert!((a.bytes_per_sec - 625_000.0).abs() < 1.0);
}
}
|
