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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 #include "net/quic/congestion_control/cubic.h" | 5 #include "net/quic/congestion_control/cubic.h" |
6 | 6 |
7 #include <algorithm> | 7 #include <algorithm> |
8 #include <cmath> | 8 #include <cmath> |
9 | 9 |
10 #include "base/basictypes.h" | 10 #include "base/basictypes.h" |
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31 | 31 |
32 const uint32 kDefaultNumConnections = 2; | 32 const uint32 kDefaultNumConnections = 2; |
33 const float kBeta = 0.7f; // Default Cubic backoff factor. | 33 const float kBeta = 0.7f; // Default Cubic backoff factor. |
34 // Additional backoff factor when loss occurs in the concave part of the Cubic | 34 // Additional backoff factor when loss occurs in the concave part of the Cubic |
35 // curve. This additional backoff factor is expected to give up bandwidth to | 35 // curve. This additional backoff factor is expected to give up bandwidth to |
36 // new concurrent flows and speed up convergence. | 36 // new concurrent flows and speed up convergence. |
37 const float kBetaLastMax = 0.85f; | 37 const float kBetaLastMax = 0.85f; |
38 | 38 |
39 } // namespace | 39 } // namespace |
40 | 40 |
41 Cubic::Cubic(const QuicClock* clock, QuicConnectionStats* stats) | 41 Cubic::Cubic(const QuicClock* clock) |
42 : clock_(clock), | 42 : clock_(clock), |
43 num_connections_(kDefaultNumConnections), | 43 num_connections_(kDefaultNumConnections), |
44 epoch_(QuicTime::Zero()), | 44 epoch_(QuicTime::Zero()), |
45 last_update_time_(QuicTime::Zero()), | 45 last_update_time_(QuicTime::Zero()) { |
46 stats_(stats) { | |
47 Reset(); | 46 Reset(); |
48 } | 47 } |
49 | 48 |
50 void Cubic::SetNumConnections(int num_connections) { | 49 void Cubic::SetNumConnections(int num_connections) { |
51 num_connections_ = num_connections; | 50 num_connections_ = num_connections; |
52 } | 51 } |
53 | 52 |
54 float Cubic::Alpha() const { | 53 float Cubic::Alpha() const { |
55 // TCPFriendly alpha is described in Section 3.3 of the CUBIC paper. Note that | 54 // TCPFriendly alpha is described in Section 3.3 of the CUBIC paper. Note that |
56 // beta here is a cwnd multiplier, and is equal to 1-beta from the paper. | 55 // beta here is a cwnd multiplier, and is equal to 1-beta from the paper. |
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72 last_update_time_ = QuicTime::Zero(); // Reset time. | 71 last_update_time_ = QuicTime::Zero(); // Reset time. |
73 last_congestion_window_ = 0; | 72 last_congestion_window_ = 0; |
74 last_max_congestion_window_ = 0; | 73 last_max_congestion_window_ = 0; |
75 acked_packets_count_ = 0; | 74 acked_packets_count_ = 0; |
76 estimated_tcp_congestion_window_ = 0; | 75 estimated_tcp_congestion_window_ = 0; |
77 origin_point_congestion_window_ = 0; | 76 origin_point_congestion_window_ = 0; |
78 time_to_origin_point_ = 0; | 77 time_to_origin_point_ = 0; |
79 last_target_congestion_window_ = 0; | 78 last_target_congestion_window_ = 0; |
80 } | 79 } |
81 | 80 |
82 void Cubic::UpdateCongestionControlStats(QuicPacketCount new_cubic_mode_cwnd, | |
83 QuicPacketCount new_reno_mode_cwnd) { | |
84 QuicPacketCount highest_new_cwnd = max(new_cubic_mode_cwnd, | |
85 new_reno_mode_cwnd); | |
86 if (last_congestion_window_ < highest_new_cwnd) { | |
87 // cwnd will increase to highest_new_cwnd. | |
88 stats_->cwnd_increase_congestion_avoidance += | |
89 highest_new_cwnd - last_congestion_window_; | |
90 if (new_cubic_mode_cwnd > new_reno_mode_cwnd) { | |
91 // This cwnd increase is due to cubic mode. | |
92 stats_->cwnd_increase_cubic_mode += | |
93 new_cubic_mode_cwnd - last_congestion_window_; | |
94 } | |
95 } | |
96 } | |
97 | |
98 QuicPacketCount Cubic::CongestionWindowAfterPacketLoss( | 81 QuicPacketCount Cubic::CongestionWindowAfterPacketLoss( |
99 QuicPacketCount current_congestion_window) { | 82 QuicPacketCount current_congestion_window) { |
100 if (current_congestion_window < last_max_congestion_window_) { | 83 if (current_congestion_window < last_max_congestion_window_) { |
101 // We never reached the old max, so assume we are competing with another | 84 // We never reached the old max, so assume we are competing with another |
102 // flow. Use our extra back off factor to allow the other flow to go up. | 85 // flow. Use our extra back off factor to allow the other flow to go up. |
103 last_max_congestion_window_ = | 86 last_max_congestion_window_ = |
104 static_cast<int>(kBetaLastMax * current_congestion_window); | 87 static_cast<int>(kBetaLastMax * current_congestion_window); |
105 } else { | 88 } else { |
106 last_max_congestion_window_ = current_congestion_window; | 89 last_max_congestion_window_ = current_congestion_window; |
107 } | 90 } |
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164 // Update estimated TCP congestion_window. | 147 // Update estimated TCP congestion_window. |
165 QuicPacketCount required_ack_count = static_cast<QuicPacketCount>( | 148 QuicPacketCount required_ack_count = static_cast<QuicPacketCount>( |
166 estimated_tcp_congestion_window_ / Alpha()); | 149 estimated_tcp_congestion_window_ / Alpha()); |
167 if (acked_packets_count_ < required_ack_count) { | 150 if (acked_packets_count_ < required_ack_count) { |
168 break; | 151 break; |
169 } | 152 } |
170 acked_packets_count_ -= required_ack_count; | 153 acked_packets_count_ -= required_ack_count; |
171 estimated_tcp_congestion_window_++; | 154 estimated_tcp_congestion_window_++; |
172 } | 155 } |
173 | 156 |
174 // Update cubic mode and reno mode stats in QuicConnectionStats. | |
175 UpdateCongestionControlStats(target_congestion_window, | |
176 estimated_tcp_congestion_window_); | |
177 | |
178 // We have a new cubic congestion window. | 157 // We have a new cubic congestion window. |
179 last_target_congestion_window_ = target_congestion_window; | 158 last_target_congestion_window_ = target_congestion_window; |
180 | 159 |
181 // Compute target congestion_window based on cubic target and estimated TCP | 160 // Compute target congestion_window based on cubic target and estimated TCP |
182 // congestion_window, use highest (fastest). | 161 // congestion_window, use highest (fastest). |
183 if (target_congestion_window < estimated_tcp_congestion_window_) { | 162 if (target_congestion_window < estimated_tcp_congestion_window_) { |
184 target_congestion_window = estimated_tcp_congestion_window_; | 163 target_congestion_window = estimated_tcp_congestion_window_; |
185 } | 164 } |
186 | 165 |
187 DVLOG(1) << "Target congestion_window: " << target_congestion_window; | 166 DVLOG(1) << "Target congestion_window: " << target_congestion_window; |
188 return target_congestion_window; | 167 return target_congestion_window; |
189 } | 168 } |
190 | 169 |
191 } // namespace net | 170 } // namespace net |
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