| // Copyright 2015 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/quiche/src/quic/core/congestion_control/general_loss_algorithm.h" |
| |
| #include "net/third_party/quiche/src/quic/core/congestion_control/rtt_stats.h" |
| #include "net/third_party/quiche/src/quic/core/quic_packets.h" |
| #include "net/third_party/quiche/src/quic/platform/api/quic_bug_tracker.h" |
| #include "net/third_party/quiche/src/quic/platform/api/quic_flag_utils.h" |
| #include "net/third_party/quiche/src/quic/platform/api/quic_flags.h" |
| |
| namespace quic { |
| |
| namespace { |
| |
| // The minimum delay before a packet will be considered lost, |
| // regardless of SRTT. Half of the minimum TLP, since the loss algorithm only |
| // triggers when a nack has been receieved for the packet. |
| static const size_t kMinLossDelayMs = 5; |
| |
| // Default fraction of an RTT the algorithm waits before determining a packet is |
| // lost due to early retransmission by time based loss detection. |
| static const int kDefaultLossDelayShift = 2; |
| // Default fraction of an RTT when doing adaptive loss detection. |
| static const int kDefaultAdaptiveLossDelayShift = 4; |
| |
| } // namespace |
| |
| GeneralLossAlgorithm::GeneralLossAlgorithm() : GeneralLossAlgorithm(kNack) {} |
| |
| GeneralLossAlgorithm::GeneralLossAlgorithm(LossDetectionType loss_type) |
| : loss_detection_timeout_(QuicTime::Zero()), |
| least_in_flight_(1), |
| faster_detect_loss_(GetQuicReloadableFlag(quic_faster_detect_loss)) { |
| SetLossDetectionType(loss_type); |
| } |
| |
| void GeneralLossAlgorithm::SetLossDetectionType(LossDetectionType loss_type) { |
| loss_detection_timeout_ = QuicTime::Zero(); |
| largest_sent_on_spurious_retransmit_.Clear(); |
| loss_type_ = loss_type; |
| reordering_shift_ = loss_type == kAdaptiveTime |
| ? kDefaultAdaptiveLossDelayShift |
| : kDefaultLossDelayShift; |
| if (GetQuicReloadableFlag(quic_eighth_rtt_loss_detection) && |
| loss_type == kTime) { |
| QUIC_RELOADABLE_FLAG_COUNT(quic_eighth_rtt_loss_detection); |
| reordering_shift_ = 3; |
| } |
| largest_previously_acked_.Clear(); |
| } |
| |
| LossDetectionType GeneralLossAlgorithm::GetLossDetectionType() const { |
| return loss_type_; |
| } |
| |
| // Uses nack counts to decide when packets are lost. |
| void GeneralLossAlgorithm::DetectLosses( |
| const QuicUnackedPacketMap& unacked_packets, |
| QuicTime time, |
| const RttStats& rtt_stats, |
| QuicPacketNumber largest_newly_acked, |
| const AckedPacketVector& packets_acked, |
| LostPacketVector* packets_lost) { |
| loss_detection_timeout_ = QuicTime::Zero(); |
| if (faster_detect_loss_ && !packets_acked.empty() && |
| packets_acked.front().packet_number == least_in_flight_) { |
| if (least_in_flight_ + packets_acked.size() - 1 == largest_newly_acked) { |
| // Optimization for the case when no packet is missing. |
| QUIC_RELOADABLE_FLAG_COUNT_N(quic_faster_detect_loss, 1, 3); |
| least_in_flight_ = largest_newly_acked + 1; |
| largest_previously_acked_ = largest_newly_acked; |
| return; |
| } |
| QUIC_RELOADABLE_FLAG_COUNT_N(quic_faster_detect_loss, 2, 3); |
| // There is hole in acked_packets, increment least_in_flight_ if possible. |
| for (const auto& acked : packets_acked) { |
| if (acked.packet_number != least_in_flight_) { |
| break; |
| } |
| ++least_in_flight_; |
| } |
| } |
| QuicTime::Delta max_rtt = |
| std::max(rtt_stats.previous_srtt(), rtt_stats.latest_rtt()); |
| QuicTime::Delta loss_delay = |
| std::max(QuicTime::Delta::FromMilliseconds(kMinLossDelayMs), |
| max_rtt + (max_rtt >> reordering_shift_)); |
| QuicPacketNumber packet_number = unacked_packets.GetLeastUnacked(); |
| auto it = unacked_packets.begin(); |
| if (faster_detect_loss_) { |
| if (least_in_flight_.IsInitialized() && least_in_flight_ >= packet_number) { |
| if (least_in_flight_ > unacked_packets.largest_sent_packet() + 1) { |
| QUIC_BUG << "least_in_flight: " << least_in_flight_ |
| << " is greater than largest_sent_packet + 1: " |
| << unacked_packets.largest_sent_packet() + 1; |
| } else { |
| QUIC_RELOADABLE_FLAG_COUNT_N(quic_faster_detect_loss, 3, 3); |
| it += (least_in_flight_ - packet_number); |
| packet_number = least_in_flight_; |
| } |
| } |
| // Clear least_in_flight_. |
| least_in_flight_.Clear(); |
| } else { |
| if (largest_lost_.IsInitialized() && largest_lost_ >= packet_number) { |
| if (largest_lost_ > unacked_packets.largest_sent_packet()) { |
| QUIC_BUG << "largest_lost: " << largest_lost_ |
| << " is greater than largest_sent_packet: " |
| << unacked_packets.largest_sent_packet(); |
| } else { |
| it += (largest_lost_ - packet_number + 1); |
| packet_number = largest_lost_ + 1; |
| } |
| } |
| } |
| for (; it != unacked_packets.end() && packet_number <= largest_newly_acked; |
| ++it, ++packet_number) { |
| if (!it->in_flight) { |
| continue; |
| } |
| |
| if (loss_type_ == kNack) { |
| // FACK based loss detection. |
| if (largest_newly_acked - packet_number >= |
| kNumberOfNacksBeforeRetransmission) { |
| packets_lost->push_back(LostPacket(packet_number, it->bytes_sent)); |
| continue; |
| } |
| } else if (loss_type_ == kLazyFack) { |
| // Require two in order acks to invoke FACK, which avoids spuriously |
| // retransmitting packets when one packet is reordered by a large amount. |
| if (largest_previously_acked_.IsInitialized() && |
| largest_newly_acked > largest_previously_acked_ && |
| largest_previously_acked_ > packet_number && |
| largest_previously_acked_ - packet_number >= |
| (kNumberOfNacksBeforeRetransmission - 1)) { |
| packets_lost->push_back(LostPacket(packet_number, it->bytes_sent)); |
| continue; |
| } |
| } |
| |
| // Only early retransmit(RFC5827) when the last packet gets acked and |
| // there are retransmittable packets in flight. |
| // This also implements a timer-protected variant of FACK. |
| if (unacked_packets.largest_sent_retransmittable_packet() <= |
| largest_newly_acked || |
| loss_type_ == kTime || loss_type_ == kAdaptiveTime) { |
| QuicTime when_lost = it->sent_time + loss_delay; |
| if (time < when_lost) { |
| loss_detection_timeout_ = when_lost; |
| if (!least_in_flight_.IsInitialized()) { |
| // At this point, packet_number is in flight and not detected as lost. |
| least_in_flight_ = packet_number; |
| } |
| break; |
| } |
| packets_lost->push_back(LostPacket(packet_number, it->bytes_sent)); |
| continue; |
| } |
| |
| // NACK-based loss detection allows for a max reordering window of 1 RTT. |
| if (it->sent_time + rtt_stats.smoothed_rtt() < |
| unacked_packets.GetTransmissionInfo(largest_newly_acked).sent_time) { |
| packets_lost->push_back(LostPacket(packet_number, it->bytes_sent)); |
| continue; |
| } |
| if (!least_in_flight_.IsInitialized()) { |
| // At this point, packet_number is in flight and not detected as lost. |
| least_in_flight_ = packet_number; |
| } |
| } |
| if (!least_in_flight_.IsInitialized()) { |
| // There is no in flight packet. |
| least_in_flight_ = largest_newly_acked + 1; |
| } |
| largest_previously_acked_ = largest_newly_acked; |
| if (!packets_lost->empty()) { |
| DCHECK(!largest_lost_.IsInitialized() || |
| largest_lost_ < packets_lost->back().packet_number); |
| largest_lost_ = packets_lost->back().packet_number; |
| } |
| } |
| |
| QuicTime GeneralLossAlgorithm::GetLossTimeout() const { |
| return loss_detection_timeout_; |
| } |
| |
| void GeneralLossAlgorithm::SpuriousRetransmitDetected( |
| const QuicUnackedPacketMap& unacked_packets, |
| QuicTime time, |
| const RttStats& rtt_stats, |
| QuicPacketNumber spurious_retransmission) { |
| if (loss_type_ != kAdaptiveTime || reordering_shift_ == 0) { |
| return; |
| } |
| // Calculate the extra time needed so this wouldn't have been declared lost. |
| // Extra time needed is based on how long it's been since the spurious |
| // retransmission was sent, because the SRTT and latest RTT may have changed. |
| QuicTime::Delta extra_time_needed = |
| time - |
| unacked_packets.GetTransmissionInfo(spurious_retransmission).sent_time; |
| // Increase the reordering fraction until enough time would be allowed. |
| QuicTime::Delta max_rtt = |
| std::max(rtt_stats.previous_srtt(), rtt_stats.latest_rtt()); |
| if (GetQuicReloadableFlag(quic_fix_adaptive_time_loss)) { |
| QUIC_RELOADABLE_FLAG_COUNT(quic_fix_adaptive_time_loss); |
| while ((max_rtt >> reordering_shift_) <= extra_time_needed && |
| reordering_shift_ > 0) { |
| --reordering_shift_; |
| } |
| return; |
| } |
| |
| if (largest_sent_on_spurious_retransmit_.IsInitialized() && |
| spurious_retransmission <= largest_sent_on_spurious_retransmit_) { |
| return; |
| } |
| largest_sent_on_spurious_retransmit_ = unacked_packets.largest_sent_packet(); |
| QuicTime::Delta proposed_extra_time(QuicTime::Delta::Zero()); |
| do { |
| proposed_extra_time = max_rtt >> reordering_shift_; |
| --reordering_shift_; |
| } while (proposed_extra_time < extra_time_needed && reordering_shift_ > 0); |
| } |
| |
| } // namespace quic |