mirror of
https://github.com/tailscale/tailscale.git
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a7fe1d7c46
The old decay-based one took a while to converge. This new one (based very loosely on TCP BBR) seems to converge quickly on what seems to be the best speed. Signed-off-by: Avery Pennarun <apenwarr@tailscale.com>
263 lines
6.6 KiB
Go
263 lines
6.6 KiB
Go
// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import (
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"encoding/binary"
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"fmt"
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"log"
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"sync"
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"time"
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"inet.af/netaddr"
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"tailscale.com/net/packet"
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"tailscale.com/types/ipproto"
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)
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type Snapshot struct {
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WhenNsec int64 // current time
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timeAcc int64 // accumulated time (+NSecPerTx per transmit)
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LastSeqTx int64 // last sequence number sent
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LastSeqRx int64 // last sequence number received
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TotalLost int64 // packets out-of-order or lost so far
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TotalOOO int64 // packets out-of-order so far
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TotalBytesRx int64 // total bytes received so far
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}
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type Delta struct {
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DurationNsec int64
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TxPackets int64
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RxPackets int64
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LostPackets int64
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OOOPackets int64
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Bytes int64
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}
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func (b Snapshot) Sub(a Snapshot) Delta {
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return Delta{
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DurationNsec: b.WhenNsec - a.WhenNsec,
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TxPackets: b.LastSeqTx - a.LastSeqTx,
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RxPackets: (b.LastSeqRx - a.LastSeqRx) -
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(b.TotalLost - a.TotalLost) +
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(b.TotalOOO - a.TotalOOO),
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LostPackets: b.TotalLost - a.TotalLost,
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OOOPackets: b.TotalOOO - a.TotalOOO,
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Bytes: b.TotalBytesRx - a.TotalBytesRx,
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}
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}
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func (d Delta) String() string {
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return fmt.Sprintf("tx=%-6d rx=%-4d (%6d = %.1f%% loss) (%d OOO) (%4.1f Mbit/s)",
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d.TxPackets, d.RxPackets, d.LostPackets,
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float64(d.LostPackets)*100/float64(d.TxPackets),
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d.OOOPackets,
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float64(d.Bytes)*8*1e9/float64(d.DurationNsec)/1e6)
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}
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type TrafficGen struct {
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mu sync.Mutex
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cur, prev Snapshot // snapshots used for rate control
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buf []byte // pre-generated packet buffer
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done bool // true if the test has completed
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onFirstPacket func() // function to call on first received packet
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// maxPackets is the max packets to receive (not send) before
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// ending the test. If it's zero, the test runs forever.
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maxPackets int64
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// nsPerPacket is the target average nanoseconds between packets.
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// It's initially zero, which means transmit as fast as the
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// caller wants to go.
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nsPerPacket int64
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// ppsHistory is the observed packets-per-second from recent
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// samples.
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ppsHistory [5]int64
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}
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// NewTrafficGen creates a new, initially locked, TrafficGen.
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// Until Start() is called, Generate() will block forever.
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func NewTrafficGen(onFirstPacket func()) *TrafficGen {
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t := TrafficGen{
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onFirstPacket: onFirstPacket,
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}
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// initially locked, until first Start()
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t.mu.Lock()
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return &t
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}
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// Start starts the traffic generator. It assumes mu is already locked,
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// and unlocks it.
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func (t *TrafficGen) Start(src, dst netaddr.IP, bytesPerPacket int, maxPackets int64) {
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h12 := packet.ICMP4Header{
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IP4Header: packet.IP4Header{
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IPProto: ipproto.ICMPv4,
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IPID: 0,
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Src: src,
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Dst: dst,
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},
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Type: packet.ICMP4EchoRequest,
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Code: packet.ICMP4NoCode,
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}
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// ensure there's room for ICMP header plus sequence number
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if bytesPerPacket < ICMPMinSize+8 {
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log.Fatalf("bytesPerPacket must be > 24+8")
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}
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t.maxPackets = maxPackets
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payload := make([]byte, bytesPerPacket-ICMPMinSize)
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t.buf = packet.Generate(h12, payload)
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t.mu.Unlock()
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}
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func (t *TrafficGen) Snap() Snapshot {
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t.mu.Lock()
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defer t.mu.Unlock()
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t.cur.WhenNsec = time.Now().UnixNano()
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return t.cur
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}
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func (t *TrafficGen) Running() bool {
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t.mu.Lock()
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defer t.mu.Unlock()
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return !t.done
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}
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// Generate produces the next packet in the sequence. It sleeps if
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// it's too soon for the next packet to be sent.
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//
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// The generated packet is placed into buf at offset ofs, for compatibility
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// with the wireguard-go conventions.
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//
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// The return value is the number of bytes generated in the packet, or 0
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// if the test has finished running.
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func (t *TrafficGen) Generate(b []byte, ofs int) int {
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t.mu.Lock()
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now := time.Now().UnixNano()
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if t.nsPerPacket == 0 || t.cur.timeAcc == 0 {
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t.cur.timeAcc = now - 1
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}
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if t.cur.timeAcc >= now {
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// too soon
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t.mu.Unlock()
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time.Sleep(time.Duration(t.cur.timeAcc-now) * time.Nanosecond)
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t.mu.Lock()
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now = t.cur.timeAcc
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}
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if t.done {
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t.mu.Unlock()
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return 0
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}
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t.cur.timeAcc += t.nsPerPacket
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t.cur.LastSeqTx += 1
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t.cur.WhenNsec = now
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seq := t.cur.LastSeqTx
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t.mu.Unlock()
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copy(b[ofs:], t.buf)
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binary.BigEndian.PutUint64(
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b[ofs+ICMPMinSize:ofs+ICMPMinSize+8],
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uint64(seq))
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return len(t.buf)
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}
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// GotPacket processes a packet that came back on the receive side.
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func (t *TrafficGen) GotPacket(b []byte, ofs int) {
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t.mu.Lock()
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s := &t.cur
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seq := int64(binary.BigEndian.Uint64(
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b[ofs+ICMPMinSize : ofs+ICMPMinSize+8]))
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if seq > s.LastSeqRx {
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if s.LastSeqRx > 0 {
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// only count lost packets after the very first
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// successful one.
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s.TotalLost += seq - s.LastSeqRx - 1
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}
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s.LastSeqRx = seq
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} else {
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s.TotalOOO += 1
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}
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// +1 packet since we only start counting after the first one
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if t.maxPackets > 0 && s.LastSeqRx >= t.maxPackets+1 {
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t.done = true
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}
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s.TotalBytesRx += int64(len(b) - ofs)
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f := t.onFirstPacket
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t.onFirstPacket = nil
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t.mu.Unlock()
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if f != nil {
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f()
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}
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}
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// Adjust tunes the transmit rate based on the received packets.
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// The goal is to converge on the fastest transmit rate that still has
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// minimal packet loss. Returns the new target rate in packets/sec.
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//
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// We need to play this guessing game in order to balance out tx and rx
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// rates when there's a lossy network between them. Otherwise we can end
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// up using 99% of the CPU to blast out transmitted packets and leaving only
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// 1% to receive them, leading to a misleading throughput calculation.
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//
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// Call this function multiple times per second.
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func (t *TrafficGen) Adjust() (pps int64) {
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t.mu.Lock()
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defer t.mu.Unlock()
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d := t.cur.Sub(t.prev)
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// don't adjust rate until the first full period *after* receiving
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// the first packet. This skips any handshake time in the underlying
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// transport.
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if t.prev.LastSeqRx == 0 || d.DurationNsec == 0 {
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t.prev = t.cur
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return 0 // no estimate yet, continue at max speed
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}
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pps = int64(d.RxPackets) * 1e9 / int64(d.DurationNsec)
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// We use a rate selection algorithm based loosely on TCP BBR.
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// Basically, we set the transmit rate to be a bit higher than
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// the best observed transmit rate in the last several time
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// periods. This guarantees some packet loss, but should converge
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// quickly on a rate near the sustainable maximum.
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bestPPS := pps
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for _, p := range t.ppsHistory {
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if p > bestPPS {
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bestPPS = p
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}
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}
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if pps > 0 && t.prev.WhenNsec > 0 {
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copy(t.ppsHistory[1:], t.ppsHistory[0:len(t.ppsHistory)-1])
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t.ppsHistory[0] = pps
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}
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if bestPPS > 0 {
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pps = bestPPS * 103 / 100
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t.nsPerPacket = int64(1e9 / pps)
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}
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t.prev = t.cur
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return pps
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}
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