net/quic/quic_flow_controller.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/quic/quic_flow_controller.h"
   6
   7 #include "base/basictypes.h"
   8 #include "net/quic/quic_connection.h"
   9 #include "net/quic/quic_flags.h"
  10 #include "net/quic/quic_protocol.h"
  11
  12 namespace net {
  13
  14 namespace {
  15 const QuicByteCount kStreamReceiveWindowLimit = 16 * 1024 * 1024;   // 16 MB
  16 const QuicByteCount kSessionReceiveWindowLimit = 24 * 1024 * 1024;  // 24 MB
  17 }
  18
  19 #define ENDPOINT \
  20   (perspective_ == Perspective::IS_SERVER ? "Server: " : "Client: ")
  21
  22 QuicFlowController::QuicFlowController(QuicConnection* connection,
  23                                        QuicStreamId id,
  24                                        Perspective perspective,
  25                                        QuicStreamOffset send_window_offset,
  26                                        QuicStreamOffset receive_window_offset,
  27                                        bool should_auto_tune_receive_window)
  28     : connection_(connection),
  29       id_(id),
  30       perspective_(perspective),
  31       bytes_sent_(0),
  32       send_window_offset_(send_window_offset),
  33       bytes_consumed_(0),
  34       highest_received_byte_offset_(0),
  35       receive_window_offset_(receive_window_offset),
  36       receive_window_size_(receive_window_offset),
  37       auto_tune_receive_window_(should_auto_tune_receive_window),
  38       last_blocked_send_window_offset_(0),
  39       prev_window_update_time_(QuicTime::Zero()) {
  40   receive_window_size_limit_ = (id_ == kConnectionLevelId)
  41                                    ? kSessionReceiveWindowLimit
  42                                    : kStreamReceiveWindowLimit;
  43
  44   DVLOG(1) << ENDPOINT << "Created flow controller for stream " << id_
  45            << ", setting initial receive window offset to: "
  46            << receive_window_offset_
  47            << ", max receive window to: " << receive_window_size_
  48            << ", max receive window limit to: " << receive_window_size_limit_
  49            << ", setting send window offset to: " << send_window_offset_;
  50 }
  51
  52 void QuicFlowController::AddBytesConsumed(QuicByteCount bytes_consumed) {
  53   bytes_consumed_ += bytes_consumed;
  54   DVLOG(1) << ENDPOINT << "Stream " << id_ << " consumed: " << bytes_consumed_;
  55
  56   MaybeSendWindowUpdate();
  57 }
  58
  59 bool QuicFlowController::UpdateHighestReceivedOffset(
  60     QuicStreamOffset new_offset) {
  61   // Only update if offset has increased.
  62   if (new_offset <= highest_received_byte_offset_) {
  63     return false;
  64   }
  65
  66   DVLOG(1) << ENDPOINT << "Stream " << id_
  67            << " highest byte offset increased from: "
  68            << highest_received_byte_offset_ << " to " << new_offset;
  69   highest_received_byte_offset_ = new_offset;
  70   return true;
  71 }
  72
  73 void QuicFlowController::AddBytesSent(QuicByteCount bytes_sent) {
  74   if (bytes_sent_ + bytes_sent > send_window_offset_) {
  75     LOG(DFATAL) << ENDPOINT << "Stream " << id_ << " Trying to send an extra "
  76                 << bytes_sent << " bytes, when bytes_sent = " << bytes_sent_
  77                 << ", and send_window_offset_ = " << send_window_offset_;
  78     bytes_sent_ = send_window_offset_;
  79
  80     // This is an error on our side, close the connection as soon as possible.
  81     connection_->SendConnectionClose(QUIC_FLOW_CONTROL_SENT_TOO_MUCH_DATA);
  82     return;
  83   }
  84
  85   bytes_sent_ += bytes_sent;
  86   DVLOG(1) << ENDPOINT << "Stream " << id_ << " sent: " << bytes_sent_;
  87 }
  88
  89 bool QuicFlowController::FlowControlViolation() {
  90   if (highest_received_byte_offset_ > receive_window_offset_) {
  91     LOG(ERROR) << ENDPOINT << "Flow control violation on stream "
  92                << id_ << ", receive window offset: "
  93                << receive_window_offset_
  94                << ", highest received byte offset: "
  95                << highest_received_byte_offset_;
  96     return true;
  97   }
  98   return false;
  99 }
 100
 101 void QuicFlowController::MaybeIncreaseMaxWindowSize() {
 102   // Core of receive window auto tuning.  This method should be called before a
 103   // WINDOW_UPDATE frame is sent.  Ideally, window updates should occur close to
 104   // once per RTT.  If a window update happens much faster than RTT, it implies
 105   // that the flow control window is imposing a bottleneck.  To prevent this,
 106   // this method will increase the receive window size (subject to a reasonable
 107   // upper bound).  For simplicity this algorithm is deliberately asymmetric, in
 108   // that it may increase window size but never decreases.
 109
 110   if (!FLAGS_quic_auto_tune_receive_window) {
 111     return;
 112   }
 113
 114   // Keep track of timing between successive window updates.
 115   QuicTime now = connection_->clock()->ApproximateNow();
 116   QuicTime prev = prev_window_update_time_;
 117   prev_window_update_time_ = now;
 118   if (!prev.IsInitialized()) {
 119     DVLOG(1) << ENDPOINT << "first window update for stream " << id_;
 120     return;
 121   }
 122
 123   if (!auto_tune_receive_window_) {
 124     return;
 125   }
 126
 127   // Get outbound RTT.
 128   QuicTime::Delta rtt =
 129       connection_->sent_packet_manager().GetRttStats()->smoothed_rtt();
 130   if (rtt.IsZero()) {
 131     DVLOG(1) << ENDPOINT << "rtt zero for stream " << id_;
 132     return;
 133   }
 134
 135   // Now we can compare timing of window updates with RTT.
 136   QuicTime::Delta since_last = now.Subtract(prev);
 137   QuicTime::Delta two_rtt = rtt.Multiply(2);
 138
 139   if (since_last >= two_rtt) {
 140     // If interval between window updates is sufficiently large, there
 141     // is no need to increase receive_window_size_.
 142     return;
 143   }
 144
 145   QuicByteCount old_window = receive_window_size_;
 146   receive_window_size_ *= 2;
 147   receive_window_size_ =
 148       std::min(receive_window_size_, receive_window_size_limit_);
 149
 150   if (receive_window_size_ > old_window) {
 151     DVLOG(1) << ENDPOINT << "New max window increase for stream " << id_
 152              << " after " << since_last.ToMicroseconds() << " us, and RTT is "
 153              << rtt.ToMicroseconds()
 154              << "us. max wndw: " << receive_window_size_;
 155   } else {
 156     // TODO(ckrasic) - add a varz to track this (?).
 157     DVLOG(1) << ENDPOINT << "Max window at limit for stream " << id_
 158              << " after " << since_last.ToMicroseconds() << " us, and RTT is "
 159              << rtt.ToMicroseconds()
 160              << "us. Limit size: " << receive_window_size_;
 161   }
 162 }
 163
 164 QuicByteCount QuicFlowController::WindowUpdateThreshold() {
 165   return receive_window_size_ / 2;
 166 }
 167
 168 void QuicFlowController::MaybeSendWindowUpdate() {
 169   // Send WindowUpdate to increase receive window if
 170   // (receive window offset - consumed bytes) < (max window / 2).
 171   // This is behaviour copied from SPDY.
 172   DCHECK_LE(bytes_consumed_, receive_window_offset_);
 173   QuicStreamOffset available_window = receive_window_offset_ - bytes_consumed_;
 174   QuicByteCount threshold = WindowUpdateThreshold();
 175
 176   if (available_window >= threshold) {
 177     DVLOG(1) << ENDPOINT << "Not sending WindowUpdate for stream " << id_
 178              << ", available window: " << available_window
 179              << ">= threshold: " << threshold;
 180     return;
 181   }
 182
 183   MaybeIncreaseMaxWindowSize();
 184
 185   // Update our receive window.
 186   receive_window_offset_ += (receive_window_size_ - available_window);
 187
 188   DVLOG(1) << ENDPOINT << "Sending WindowUpdate frame for stream " << id_
 189            << ", consumed bytes: " << bytes_consumed_
 190            << ", available window: " << available_window
 191            << ", and threshold: " << threshold
 192            << ", and receive window size: " << receive_window_size_
 193            << ". New receive window offset is: " << receive_window_offset_;
 194
 195   // Inform the peer of our new receive window.
 196   connection_->SendWindowUpdate(id_, receive_window_offset_);
 197 }
 198
 199 void QuicFlowController::MaybeSendBlocked() {
 200   if (SendWindowSize() == 0 &&
 201       last_blocked_send_window_offset_ < send_window_offset_) {
 202     DVLOG(1) << ENDPOINT << "Stream " << id_ << " is flow control blocked. "
 203              << "Send window: " << SendWindowSize()
 204              << ", bytes sent: " << bytes_sent_
 205              << ", send limit: " << send_window_offset_;
 206     // The entire send_window has been consumed, we are now flow control
 207     // blocked.
 208     connection_->SendBlocked(id_);
 209
 210     // Keep track of when we last sent a BLOCKED frame so that we only send one
 211     // at a given send offset.
 212     last_blocked_send_window_offset_ = send_window_offset_;
 213   }
 214 }
 215
 216 bool QuicFlowController::UpdateSendWindowOffset(
 217     QuicStreamOffset new_send_window_offset) {
 218   // Only update if send window has increased.
 219   if (new_send_window_offset <= send_window_offset_) {
 220     return false;
 221   }
 222
 223   DVLOG(1) << ENDPOINT << "UpdateSendWindowOffset for stream " << id_
 224            << " with new offset " << new_send_window_offset
 225            << " current offset: " << send_window_offset_
 226            << " bytes_sent: " << bytes_sent_;
 227
 228   const bool blocked = IsBlocked();
 229   send_window_offset_ = new_send_window_offset;
 230   return blocked;
 231 }
 232
 233 bool QuicFlowController::IsBlocked() const {
 234   return SendWindowSize() == 0;
 235 }
 236
 237 uint64 QuicFlowController::SendWindowSize() const {
 238   if (bytes_sent_ > send_window_offset_) {
 239     return 0;
 240   }
 241   return send_window_offset_ - bytes_sent_;
 242 }
 243
 244 }  // namespace net