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// Copyright 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 "net/third_party/quic/core/quic_received_packet_manager.h"
#include <algorithm>
#include <limits>
#include <utility>
#include "net/third_party/quic/core/congestion_control/rtt_stats.h"
#include "net/third_party/quic/core/crypto/crypto_protocol.h"
#include "net/third_party/quic/core/quic_connection_stats.h"
#include "net/third_party/quic/platform/api/quic_bug_tracker.h"
#include "net/third_party/quic/platform/api/quic_logging.h"
namespace quic {
namespace {
// The maximum number of packets to ack immediately after a missing packet for
// fast retransmission to kick in at the sender. This limit is created to
// reduce the number of acks sent that have no benefit for fast retransmission.
// Set to the number of nacks needed for fast retransmit plus one for protection
// against an ack loss
const size_t kMaxPacketsAfterNewMissing = 4;
// Maximum number of retransmittable packets received before sending an ack.
const QuicPacketCount kDefaultRetransmittablePacketsBeforeAck = 2;
// Minimum number of packets received before ack decimation is enabled.
// This intends to avoid the beginning of slow start, when CWNDs may be
// rapidly increasing.
const QuicPacketCount kMinReceivedBeforeAckDecimation = 100;
// Wait for up to 10 retransmittable packets before sending an ack.
const QuicPacketCount kMaxRetransmittablePacketsBeforeAck = 10;
// One quarter RTT delay when doing ack decimation.
const float kAckDecimationDelay = 0.25;
// One eighth RTT delay when doing ack decimation.
const float kShortAckDecimationDelay = 0.125;
} // namespace
QuicReceivedPacketManager::QuicReceivedPacketManager(QuicConnectionStats* stats)
: ack_frame_updated_(false),
max_ack_ranges_(0),
time_largest_observed_(QuicTime::Zero()),
save_timestamps_(false),
stats_(stats),
ack_mode_(GetQuicReloadableFlag(quic_enable_ack_decimation)
? ACK_DECIMATION
: TCP_ACKING),
num_retransmittable_packets_received_since_last_ack_sent_(0),
min_received_before_ack_decimation_(kMinReceivedBeforeAckDecimation),
ack_frequency_before_ack_decimation_(
kDefaultRetransmittablePacketsBeforeAck),
ack_decimation_delay_(kAckDecimationDelay),
unlimited_ack_decimation_(false),
fast_ack_after_quiescence_(false),
ack_timeout_(QuicTime::Zero()),
time_of_previous_received_packet_(QuicTime::Zero()),
was_last_packet_missing_(false),
decide_when_to_send_acks_(
GetQuicReloadableFlag(quic_deprecate_ack_bundling_mode) &&
GetQuicReloadableFlag(quic_rpm_decides_when_to_send_acks)) {}
QuicReceivedPacketManager::~QuicReceivedPacketManager() {}
void QuicReceivedPacketManager::SetFromConfig(const QuicConfig& config,
Perspective perspective) {
DCHECK(decide_when_to_send_acks_);
if (GetQuicReloadableFlag(quic_enable_ack_decimation) &&
config.HasClientSentConnectionOption(kACD0, perspective)) {
ack_mode_ = TCP_ACKING;
}
if (config.HasClientSentConnectionOption(kACKD, perspective)) {
ack_mode_ = ACK_DECIMATION;
}
if (config.HasClientSentConnectionOption(kAKD2, perspective)) {
ack_mode_ = ACK_DECIMATION_WITH_REORDERING;
}
if (config.HasClientSentConnectionOption(kAKD3, perspective)) {
ack_mode_ = ACK_DECIMATION;
ack_decimation_delay_ = kShortAckDecimationDelay;
}
if (config.HasClientSentConnectionOption(kAKD4, perspective)) {
ack_mode_ = ACK_DECIMATION_WITH_REORDERING;
ack_decimation_delay_ = kShortAckDecimationDelay;
}
if (config.HasClientSentConnectionOption(kAKDU, perspective)) {
unlimited_ack_decimation_ = true;
}
if (config.HasClientSentConnectionOption(kACKQ, perspective)) {
fast_ack_after_quiescence_ = true;
}
}
void QuicReceivedPacketManager::RecordPacketReceived(
const QuicPacketHeader& header,
QuicTime receipt_time) {
const QuicPacketNumber packet_number = header.packet_number;
DCHECK(IsAwaitingPacket(packet_number)) << " packet_number:" << packet_number;
if (decide_when_to_send_acks_) {
was_last_packet_missing_ = IsMissing(packet_number);
}
if (!ack_frame_updated_) {
ack_frame_.received_packet_times.clear();
}
ack_frame_updated_ = true;
if (LargestAcked(ack_frame_).IsInitialized() &&
LargestAcked(ack_frame_) > packet_number) {
// Record how out of order stats.
++stats_->packets_reordered;
stats_->max_sequence_reordering =
std::max(stats_->max_sequence_reordering,
LargestAcked(ack_frame_) - packet_number);
int64_t reordering_time_us =
(receipt_time - time_largest_observed_).ToMicroseconds();
stats_->max_time_reordering_us =
std::max(stats_->max_time_reordering_us, reordering_time_us);
}
if (!LargestAcked(ack_frame_).IsInitialized() ||
packet_number > LargestAcked(ack_frame_)) {
ack_frame_.largest_acked = packet_number;
time_largest_observed_ = receipt_time;
}
ack_frame_.packets.Add(packet_number);
if (save_timestamps_) {
// The timestamp format only handles packets in time order.
if (!ack_frame_.received_packet_times.empty() &&
ack_frame_.received_packet_times.back().second > receipt_time) {
LOG(WARNING)
<< "Receive time went backwards from: "
<< ack_frame_.received_packet_times.back().second.ToDebuggingValue()
<< " to " << receipt_time.ToDebuggingValue();
} else {
ack_frame_.received_packet_times.push_back(
std::make_pair(packet_number, receipt_time));
}
}
if (least_received_packet_number_.IsInitialized()) {
least_received_packet_number_ =
std::min(least_received_packet_number_, packet_number);
} else {
least_received_packet_number_ = packet_number;
}
}
bool QuicReceivedPacketManager::IsMissing(QuicPacketNumber packet_number) {
return LargestAcked(ack_frame_).IsInitialized() &&
packet_number < LargestAcked(ack_frame_) &&
!ack_frame_.packets.Contains(packet_number);
}
bool QuicReceivedPacketManager::IsAwaitingPacket(
QuicPacketNumber packet_number) {
return quic::IsAwaitingPacket(ack_frame_, packet_number,
peer_least_packet_awaiting_ack_);
}
const QuicFrame QuicReceivedPacketManager::GetUpdatedAckFrame(
QuicTime approximate_now) {
if (!decide_when_to_send_acks_) {
ack_frame_updated_ = false;
}
if (time_largest_observed_ == QuicTime::Zero()) {
// We have received no packets.
ack_frame_.ack_delay_time = QuicTime::Delta::Infinite();
} else {
// Ensure the delta is zero if approximate now is "in the past".
ack_frame_.ack_delay_time = approximate_now < time_largest_observed_
? QuicTime::Delta::Zero()
: approximate_now - time_largest_observed_;
}
while (max_ack_ranges_ > 0 &&
ack_frame_.packets.NumIntervals() > max_ack_ranges_) {
ack_frame_.packets.RemoveSmallestInterval();
}
// Clear all packet times if any are too far from largest observed.
// It's expected this is extremely rare.
for (auto it = ack_frame_.received_packet_times.begin();
it != ack_frame_.received_packet_times.end();) {
if (LargestAcked(ack_frame_) - it->first >=
std::numeric_limits<uint8_t>::max()) {
it = ack_frame_.received_packet_times.erase(it);
} else {
++it;
}
}
return QuicFrame(&ack_frame_);
}
void QuicReceivedPacketManager::DontWaitForPacketsBefore(
QuicPacketNumber least_unacked) {
if (!least_unacked.IsInitialized()) {
return;
}
// ValidateAck() should fail if peer_least_packet_awaiting_ack shrinks.
DCHECK(!peer_least_packet_awaiting_ack_.IsInitialized() ||
peer_least_packet_awaiting_ack_ <= least_unacked);
if (!peer_least_packet_awaiting_ack_.IsInitialized() ||
least_unacked > peer_least_packet_awaiting_ack_) {
peer_least_packet_awaiting_ack_ = least_unacked;
bool packets_updated = ack_frame_.packets.RemoveUpTo(least_unacked);
if (packets_updated) {
// Ack frame gets updated because packets set is updated because of stop
// waiting frame.
ack_frame_updated_ = true;
}
}
DCHECK(ack_frame_.packets.Empty() ||
!peer_least_packet_awaiting_ack_.IsInitialized() ||
ack_frame_.packets.Min() >= peer_least_packet_awaiting_ack_);
}
void QuicReceivedPacketManager::MaybeUpdateAckTimeout(
bool should_last_packet_instigate_acks,
QuicPacketNumber last_received_packet_number,
QuicTime time_of_last_received_packet,
QuicTime now,
const RttStats* rtt_stats,
QuicTime::Delta delayed_ack_time) {
DCHECK(decide_when_to_send_acks_);
if (!ack_frame_updated_) {
// ACK frame has not been updated, nothing to do.
return;
}
if (was_last_packet_missing_ && last_sent_largest_acked_.IsInitialized() &&
last_received_packet_number < last_sent_largest_acked_) {
// Only ack immediately if an ACK frame was sent with a larger largest acked
// than the newly received packet number.
ack_timeout_ = now;
return;
}
if (!should_last_packet_instigate_acks) {
return;
}
++num_retransmittable_packets_received_since_last_ack_sent_;
if (ack_mode_ != TCP_ACKING &&
last_received_packet_number >= PeerFirstSendingPacketNumber() +
min_received_before_ack_decimation_) {
// Ack up to 10 packets at once unless ack decimation is unlimited.
if (!unlimited_ack_decimation_ &&
num_retransmittable_packets_received_since_last_ack_sent_ >=
kMaxRetransmittablePacketsBeforeAck) {
ack_timeout_ = now;
return;
}
// Wait for the minimum of the ack decimation delay or the delayed ack time
// before sending an ack.
QuicTime::Delta ack_delay = std::min(
delayed_ack_time, rtt_stats->min_rtt() * ack_decimation_delay_);
if (fast_ack_after_quiescence_ && now - time_of_previous_received_packet_ >
rtt_stats->SmoothedOrInitialRtt()) {
// Ack the first packet out of queiscence faster, because QUIC does
// not pace the first few packets and commonly these may be handshake
// or TLP packets, which we'd like to acknowledge quickly.
ack_delay = QuicTime::Delta::FromMilliseconds(1);
}
MaybeUpdateAckTimeoutTo(now + ack_delay);
} else {
// Ack with a timer or every 2 packets by default.
if (num_retransmittable_packets_received_since_last_ack_sent_ >=
ack_frequency_before_ack_decimation_) {
ack_timeout_ = now;
} else if (fast_ack_after_quiescence_ &&
(now - time_of_previous_received_packet_) >
rtt_stats->SmoothedOrInitialRtt()) {
// Ack the first packet out of queiscence faster, because QUIC does
// not pace the first few packets and commonly these may be handshake
// or TLP packets, which we'd like to acknowledge quickly.
MaybeUpdateAckTimeoutTo(now + QuicTime::Delta::FromMilliseconds(1));
} else {
MaybeUpdateAckTimeoutTo(now + delayed_ack_time);
}
}
// If there are new missing packets to report, send an ack immediately.
if (HasNewMissingPackets()) {
if (ack_mode_ == ACK_DECIMATION_WITH_REORDERING) {
// Wait the minimum of an eighth min_rtt and the existing ack time.
QuicTime ack_time = now + kShortAckDecimationDelay * rtt_stats->min_rtt();
MaybeUpdateAckTimeoutTo(ack_time);
} else {
ack_timeout_ = now;
}
}
if (fast_ack_after_quiescence_) {
time_of_previous_received_packet_ = time_of_last_received_packet;
}
}
void QuicReceivedPacketManager::ResetAckStates() {
DCHECK(decide_when_to_send_acks_);
ack_frame_updated_ = false;
ack_timeout_ = QuicTime::Zero();
num_retransmittable_packets_received_since_last_ack_sent_ = 0;
last_sent_largest_acked_ = LargestAcked(ack_frame_);
}
void QuicReceivedPacketManager::MaybeUpdateAckTimeoutTo(QuicTime time) {
DCHECK(decide_when_to_send_acks_);
if (!ack_timeout_.IsInitialized() || ack_timeout_ > time) {
ack_timeout_ = time;
}
}
bool QuicReceivedPacketManager::HasMissingPackets() const {
if (ack_frame_.packets.Empty()) {
return false;
}
if (ack_frame_.packets.NumIntervals() > 1) {
return true;
}
if (!GetQuicRestartFlag(quic_enable_accept_random_ipn)) {
return ack_frame_.packets.Min() >
(peer_least_packet_awaiting_ack_.IsInitialized()
? peer_least_packet_awaiting_ack_
: QuicPacketNumber(1));
}
return peer_least_packet_awaiting_ack_.IsInitialized() &&
ack_frame_.packets.Min() > peer_least_packet_awaiting_ack_;
}
bool QuicReceivedPacketManager::HasNewMissingPackets() const {
return HasMissingPackets() &&
ack_frame_.packets.LastIntervalLength() <= kMaxPacketsAfterNewMissing;
}
bool QuicReceivedPacketManager::ack_frame_updated() const {
return ack_frame_updated_;
}
QuicPacketNumber QuicReceivedPacketManager::GetLargestObserved() const {
return LargestAcked(ack_frame_);
}
QuicPacketNumber QuicReceivedPacketManager::PeerFirstSendingPacketNumber()
const {
if (!GetQuicRestartFlag(quic_enable_accept_random_ipn)) {
return QuicPacketNumber(1);
}
if (!least_received_packet_number_.IsInitialized()) {
QUIC_BUG << "No packets have been received yet";
return QuicPacketNumber(1);
}
return least_received_packet_number_;
}
} // namespace quic