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Unified Diff: net/quic/congestion_control/cubic.cc

Issue 992733002: Remove //net (except for Android test stuff) and sdch (Closed) Base URL: git@github.com:domokit/mojo.git@master
Patch Set: Created 5 years, 9 months ago
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Index: net/quic/congestion_control/cubic.cc
diff --git a/net/quic/congestion_control/cubic.cc b/net/quic/congestion_control/cubic.cc
deleted file mode 100644
index dc6b89bf9d01fb5e7e0307000a7bb80509a45761..0000000000000000000000000000000000000000
--- a/net/quic/congestion_control/cubic.cc
+++ /dev/null
@@ -1,191 +0,0 @@
-// Copyright (c) 2012 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/quic/congestion_control/cubic.h"
-
-#include <algorithm>
-#include <cmath>
-
-#include "base/basictypes.h"
-#include "base/logging.h"
-#include "base/time/time.h"
-#include "net/quic/quic_flags.h"
-#include "net/quic/quic_protocol.h"
-
-using std::max;
-
-namespace net {
-
-namespace {
-
-// Constants based on TCP defaults.
-// The following constants are in 2^10 fractions of a second instead of ms to
-// allow a 10 shift right to divide.
-const int kCubeScale = 40; // 1024*1024^3 (first 1024 is from 0.100^3)
- // where 0.100 is 100 ms which is the scaling
- // round trip time.
-const int kCubeCongestionWindowScale = 410;
-const uint64 kCubeFactor = (GG_UINT64_C(1) << kCubeScale) /
- kCubeCongestionWindowScale;
-
-const uint32 kDefaultNumConnections = 2;
-const float kBeta = 0.7f; // Default Cubic backoff factor.
-// Additional backoff factor when loss occurs in the concave part of the Cubic
-// curve. This additional backoff factor is expected to give up bandwidth to
-// new concurrent flows and speed up convergence.
-const float kBetaLastMax = 0.85f;
-
-} // namespace
-
-Cubic::Cubic(const QuicClock* clock, QuicConnectionStats* stats)
- : clock_(clock),
- num_connections_(kDefaultNumConnections),
- epoch_(QuicTime::Zero()),
- last_update_time_(QuicTime::Zero()),
- stats_(stats) {
- Reset();
-}
-
-void Cubic::SetNumConnections(int num_connections) {
- num_connections_ = num_connections;
-}
-
-float Cubic::Alpha() const {
- // TCPFriendly alpha is described in Section 3.3 of the CUBIC paper. Note that
- // beta here is a cwnd multiplier, and is equal to 1-beta from the paper.
- // We derive the equivalent alpha for an N-connection emulation as:
- const float beta = Beta();
- return 3 * num_connections_ * num_connections_ * (1 - beta) / (1 + beta);
-}
-
-float Cubic::Beta() const {
- // kNConnectionBeta is the backoff factor after loss for our N-connection
- // emulation, which emulates the effective backoff of an ensemble of N
- // TCP-Reno connections on a single loss event. The effective multiplier is
- // computed as:
- return (num_connections_ - 1 + kBeta) / num_connections_;
-}
-
-void Cubic::Reset() {
- epoch_ = QuicTime::Zero(); // Reset time.
- last_update_time_ = QuicTime::Zero(); // Reset time.
- last_congestion_window_ = 0;
- last_max_congestion_window_ = 0;
- acked_packets_count_ = 0;
- estimated_tcp_congestion_window_ = 0;
- origin_point_congestion_window_ = 0;
- time_to_origin_point_ = 0;
- last_target_congestion_window_ = 0;
-}
-
-void Cubic::UpdateCongestionControlStats(QuicPacketCount new_cubic_mode_cwnd,
- QuicPacketCount new_reno_mode_cwnd) {
- QuicPacketCount highest_new_cwnd = max(new_cubic_mode_cwnd,
- new_reno_mode_cwnd);
- if (last_congestion_window_ < highest_new_cwnd) {
- // cwnd will increase to highest_new_cwnd.
- stats_->cwnd_increase_congestion_avoidance +=
- highest_new_cwnd - last_congestion_window_;
- if (new_cubic_mode_cwnd > new_reno_mode_cwnd) {
- // This cwnd increase is due to cubic mode.
- stats_->cwnd_increase_cubic_mode +=
- new_cubic_mode_cwnd - last_congestion_window_;
- }
- }
-}
-
-QuicPacketCount Cubic::CongestionWindowAfterPacketLoss(
- QuicPacketCount current_congestion_window) {
- if (current_congestion_window < last_max_congestion_window_) {
- // We never reached the old max, so assume we are competing with another
- // flow. Use our extra back off factor to allow the other flow to go up.
- last_max_congestion_window_ =
- static_cast<int>(kBetaLastMax * current_congestion_window);
- } else {
- last_max_congestion_window_ = current_congestion_window;
- }
- epoch_ = QuicTime::Zero(); // Reset time.
- return static_cast<int>(current_congestion_window * Beta());
-}
-
-QuicPacketCount Cubic::CongestionWindowAfterAck(
- QuicPacketCount current_congestion_window,
- QuicTime::Delta delay_min) {
- acked_packets_count_ += 1; // Packets acked.
- QuicTime current_time = clock_->ApproximateNow();
-
- // Cubic is "independent" of RTT, the update is limited by the time elapsed.
- if (last_congestion_window_ == current_congestion_window &&
- (current_time.Subtract(last_update_time_) <= MaxCubicTimeInterval())) {
- return max(last_target_congestion_window_,
- estimated_tcp_congestion_window_);
- }
- last_congestion_window_ = current_congestion_window;
- last_update_time_ = current_time;
-
- if (!epoch_.IsInitialized()) {
- // First ACK after a loss event.
- DVLOG(1) << "Start of epoch";
- epoch_ = current_time; // Start of epoch.
- acked_packets_count_ = 1; // Reset count.
- // Reset estimated_tcp_congestion_window_ to be in sync with cubic.
- estimated_tcp_congestion_window_ = current_congestion_window;
- if (last_max_congestion_window_ <= current_congestion_window) {
- time_to_origin_point_ = 0;
- origin_point_congestion_window_ = current_congestion_window;
- } else {
- time_to_origin_point_ =
- static_cast<uint32>(cbrt(kCubeFactor * (last_max_congestion_window_ -
- current_congestion_window)));
- origin_point_congestion_window_ =
- last_max_congestion_window_;
- }
- }
- // Change the time unit from microseconds to 2^10 fractions per second. Take
- // the round trip time in account. This is done to allow us to use shift as a
- // divide operator.
- int64 elapsed_time =
- (current_time.Add(delay_min).Subtract(epoch_).ToMicroseconds() << 10) /
- base::Time::kMicrosecondsPerSecond;
-
- int64 offset = time_to_origin_point_ - elapsed_time;
- QuicPacketCount delta_congestion_window = (kCubeCongestionWindowScale
- * offset * offset * offset) >> kCubeScale;
-
- QuicPacketCount target_congestion_window =
- origin_point_congestion_window_ - delta_congestion_window;
-
- DCHECK_LT(0u, estimated_tcp_congestion_window_);
- // With dynamic beta/alpha based on number of active streams, it is possible
- // for the required_ack_count to become much lower than acked_packets_count_
- // suddenly, leading to more than one iteration through the following loop.
- while (true) {
- // Update estimated TCP congestion_window.
- QuicPacketCount required_ack_count = static_cast<QuicPacketCount>(
- estimated_tcp_congestion_window_ / Alpha());
- if (acked_packets_count_ < required_ack_count) {
- break;
- }
- acked_packets_count_ -= required_ack_count;
- estimated_tcp_congestion_window_++;
- }
-
- // Update cubic mode and reno mode stats in QuicConnectionStats.
- UpdateCongestionControlStats(target_congestion_window,
- estimated_tcp_congestion_window_);
-
- // We have a new cubic congestion window.
- last_target_congestion_window_ = target_congestion_window;
-
- // Compute target congestion_window based on cubic target and estimated TCP
- // congestion_window, use highest (fastest).
- if (target_congestion_window < estimated_tcp_congestion_window_) {
- target_congestion_window = estimated_tcp_congestion_window_;
- }
-
- DVLOG(1) << "Target congestion_window: " << target_congestion_window;
- return target_congestion_window;
-}
-
-} // namespace net
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