blob: 7389a46995795cace738c9dd8293d6c9267ec30d [file] [log] [blame]
// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "quic/core/congestion_control/pacing_sender.h"
#include "quic/core/quic_bandwidth.h"
#include "quic/platform/api/quic_flag_utils.h"
#include "quic/platform/api/quic_flags.h"
#include "quic/platform/api/quic_logging.h"
namespace quic {
namespace {
// Configured maximum size of the burst coming out of quiescence. The burst
// is never larger than the current CWND in packets.
static const uint32_t kInitialUnpacedBurst = 10;
} // namespace
PacingSender::PacingSender()
: sender_(nullptr),
max_pacing_rate_(QuicBandwidth::Zero()),
burst_tokens_(kInitialUnpacedBurst),
ideal_next_packet_send_time_(QuicTime::Zero()),
initial_burst_size_(kInitialUnpacedBurst),
lumpy_tokens_(0),
alarm_granularity_(kAlarmGranularity),
pacing_limited_(false) {
if (GetQuicReloadableFlag(quic_donot_reset_ideal_next_packet_send_time)) {
QUIC_RELOADABLE_FLAG_COUNT(quic_donot_reset_ideal_next_packet_send_time);
}
}
PacingSender::~PacingSender() {}
void PacingSender::set_sender(SendAlgorithmInterface* sender) {
DCHECK(sender != nullptr);
sender_ = sender;
}
void PacingSender::OnCongestionEvent(bool rtt_updated,
QuicByteCount bytes_in_flight,
QuicTime event_time,
const AckedPacketVector& acked_packets,
const LostPacketVector& lost_packets) {
DCHECK(sender_ != nullptr);
if (!lost_packets.empty()) {
// Clear any burst tokens when entering recovery.
burst_tokens_ = 0;
}
sender_->OnCongestionEvent(rtt_updated, bytes_in_flight, event_time,
acked_packets, lost_packets);
}
void PacingSender::OnPacketSent(
QuicTime sent_time,
QuicByteCount bytes_in_flight,
QuicPacketNumber packet_number,
QuicByteCount bytes,
HasRetransmittableData has_retransmittable_data) {
DCHECK(sender_ != nullptr);
sender_->OnPacketSent(sent_time, bytes_in_flight, packet_number, bytes,
has_retransmittable_data);
if (has_retransmittable_data != HAS_RETRANSMITTABLE_DATA) {
return;
}
// If in recovery, the connection is not coming out of quiescence.
if (bytes_in_flight == 0 && !sender_->InRecovery()) {
// Add more burst tokens anytime the connection is leaving quiescence, but
// limit it to the equivalent of a single bulk write, not exceeding the
// current CWND in packets.
burst_tokens_ = std::min(
initial_burst_size_,
static_cast<uint32_t>(sender_->GetCongestionWindow() / kDefaultTCPMSS));
}
if (burst_tokens_ > 0) {
--burst_tokens_;
if (!GetQuicReloadableFlag(quic_donot_reset_ideal_next_packet_send_time)) {
ideal_next_packet_send_time_ = QuicTime::Zero();
}
pacing_limited_ = false;
return;
}
// The next packet should be sent as soon as the current packet has been
// transferred. PacingRate is based on bytes in flight including this packet.
QuicTime::Delta delay =
PacingRate(bytes_in_flight + bytes).TransferTime(bytes);
if (!pacing_limited_ || lumpy_tokens_ == 0) {
// Reset lumpy_tokens_ if either application or cwnd throttles sending or
// token runs out.
lumpy_tokens_ = std::max(
1u, std::min(static_cast<uint32_t>(
GetQuicFlag(FLAGS_quic_lumpy_pacing_size)),
static_cast<uint32_t>(
(sender_->GetCongestionWindow() *
GetQuicFlag(FLAGS_quic_lumpy_pacing_cwnd_fraction)) /
kDefaultTCPMSS)));
if (sender_->BandwidthEstimate() <
QuicBandwidth::FromKBitsPerSecond(1200)) {
// Below 1.2Mbps, send 1 packet at once, because one full-sized packet
// is about 10ms of queueing.
lumpy_tokens_ = 1u;
}
}
--lumpy_tokens_;
if (pacing_limited_) {
// Make up for lost time since pacing throttles the sending.
ideal_next_packet_send_time_ = ideal_next_packet_send_time_ + delay;
} else {
ideal_next_packet_send_time_ =
std::max(ideal_next_packet_send_time_ + delay, sent_time + delay);
}
// Stop making up for lost time if underlying sender prevents sending.
pacing_limited_ = sender_->CanSend(bytes_in_flight + bytes);
}
void PacingSender::OnApplicationLimited() {
// The send is application limited, stop making up for lost time.
pacing_limited_ = false;
}
void PacingSender::SetBurstTokens(uint32_t burst_tokens) {
initial_burst_size_ = burst_tokens;
burst_tokens_ = std::min(
initial_burst_size_,
static_cast<uint32_t>(sender_->GetCongestionWindow() / kDefaultTCPMSS));
}
QuicTime::Delta PacingSender::TimeUntilSend(
QuicTime now,
QuicByteCount bytes_in_flight) const {
DCHECK(sender_ != nullptr);
if (!sender_->CanSend(bytes_in_flight)) {
// The underlying sender prevents sending.
return QuicTime::Delta::Infinite();
}
if (burst_tokens_ > 0 || bytes_in_flight == 0 || lumpy_tokens_ > 0) {
// Don't pace if we have burst tokens available or leaving quiescence.
QUIC_DVLOG(1) << "Sending packet now. burst_tokens:" << burst_tokens_
<< ", bytes_in_flight:" << bytes_in_flight
<< ", lumpy_tokens:" << lumpy_tokens_;
return QuicTime::Delta::Zero();
}
// If the next send time is within the alarm granularity, send immediately.
if (ideal_next_packet_send_time_ > now + alarm_granularity_) {
QUIC_DVLOG(1) << "Delaying packet: "
<< (ideal_next_packet_send_time_ - now).ToMicroseconds();
return ideal_next_packet_send_time_ - now;
}
QUIC_DVLOG(1) << "Sending packet now. ideal_next_packet_send_time: "
<< ideal_next_packet_send_time_ << ", now: " << now;
return QuicTime::Delta::Zero();
}
QuicBandwidth PacingSender::PacingRate(QuicByteCount bytes_in_flight) const {
DCHECK(sender_ != nullptr);
if (!max_pacing_rate_.IsZero()) {
return QuicBandwidth::FromBitsPerSecond(
std::min(max_pacing_rate_.ToBitsPerSecond(),
sender_->PacingRate(bytes_in_flight).ToBitsPerSecond()));
}
return sender_->PacingRate(bytes_in_flight);
}
} // namespace quic