Remove unused windowed RTT logic from RttStats

net/quic/core/congestion_control/rtt_stats.cc

 // Copyright 2014 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/core/congestion_control/rtt_stats.h"
 
 #include <cstdlib>  // std::abs
 
 #include "net/quic/core/quic_flags.h"
 
 using std::max;
 
 namespace net {
 
 namespace {
 
 // Default initial rtt used before any samples are received.
 const int kInitialRttMs = 100;
 const float kAlpha = 0.125f;
 const float kOneMinusAlpha = (1 - kAlpha);
 const float kBeta = 0.25f;
 const float kOneMinusBeta = (1 - kBeta);
-// 10-second window length for windowed min RTT.
-const int kMinRttWindowLengthMs = 10000;
 
 }  // namespace
 
 RttStats::RttStats()
     : latest_rtt_(QuicTime::Delta::Zero()),
       min_rtt_(QuicTime::Delta::Zero()),
       smoothed_rtt_(QuicTime::Delta::Zero()),
       previous_srtt_(QuicTime::Delta::Zero()),
       mean_deviation_(QuicTime::Delta::Zero()),
-      initial_rtt_us_(kInitialRttMs * kNumMicrosPerMilli),
-      forced_windowed_min_rtt_(QuicTime::Delta::Zero()),
-      forced_windowed_min_rtt_time_(QuicTime::Zero()),
-      num_samples_for_forced_min_(0),
-      windowed_min_rtt_(
-          QuicTime::Delta::FromMilliseconds(kMinRttWindowLengthMs),
-          QuicTime::Delta::Zero(),
-          QuicTime::Zero()) {}
-
-void RttStats::SampleNewWindowedMinRtt(uint32_t num_samples) {
-  num_samples_for_forced_min_ = num_samples;
-  forced_windowed_min_rtt_ = QuicTime::Delta::Zero();
-  forced_windowed_min_rtt_time_ = QuicTime::Zero();
-}
+      initial_rtt_us_(kInitialRttMs * kNumMicrosPerMilli) {}
 
 void RttStats::ExpireSmoothedMetrics() {
   mean_deviation_ = max(mean_deviation_,
                         QuicTime::Delta::FromMicroseconds(std::abs(
                             (smoothed_rtt_ - latest_rtt_).ToMicroseconds())));
   smoothed_rtt_ = max(smoothed_rtt_, latest_rtt_);
 }
 
 // Updates the RTT based on a new sample.
 void RttStats::UpdateRtt(QuicTime::Delta send_delta,
                          QuicTime::Delta ack_delay,
                          QuicTime now) {
   if (send_delta.IsInfinite() || send_delta <= QuicTime::Delta::Zero()) {
     LOG(WARNING) << "Ignoring measured send_delta, because it's is "
                  << "either infinite, zero, or negative.  send_delta = "
                  << send_delta.ToMicroseconds();
     return;
   }
 
   // Update min_rtt_ first. min_rtt_ does not use an rtt_sample corrected for
   // ack_delay but the raw observed send_delta, since poor clock granularity at
   // the client may cause a high ack_delay to result in underestimation of the
   // min_rtt_.
   if (min_rtt_.IsZero() || min_rtt_ > send_delta) {
     min_rtt_ = send_delta;
   }
-  UpdateWindowedMinRtt(send_delta, now);
 
   // Correct for ack_delay if information received from the peer results in a
   // positive RTT sample. Otherwise, we use the send_delta as a reasonable
   // measure for smoothed_rtt.
   QuicTime::Delta rtt_sample(send_delta);
   previous_srtt_ = smoothed_rtt_;
 
   if (rtt_sample > ack_delay) {
     rtt_sample = rtt_sample - ack_delay;
   }
   latest_rtt_ = rtt_sample;
   // First time call.
   if (smoothed_rtt_.IsZero()) {
     smoothed_rtt_ = rtt_sample;
     mean_deviation_ =
         QuicTime::Delta::FromMicroseconds(rtt_sample.ToMicroseconds() / 2);
   } else {
     mean_deviation_ = QuicTime::Delta::FromMicroseconds(static_cast<int64_t>(
         kOneMinusBeta * mean_deviation_.ToMicroseconds() +
         kBeta * std::abs((smoothed_rtt_ - rtt_sample).ToMicroseconds())));
     smoothed_rtt_ = kOneMinusAlpha * smoothed_rtt_ + kAlpha * rtt_sample;
     DVLOG(1) << " smoothed_rtt(us):" << smoothed_rtt_.ToMicroseconds()
              << " mean_deviation(us):" << mean_deviation_.ToMicroseconds();
   }
 }
 
-void RttStats::UpdateWindowedMinRtt(QuicTime::Delta rtt_sample, QuicTime now) {
-  // Update windowed_min_rtt.
-  windowed_min_rtt_.Update(rtt_sample, now);
-  if (num_samples_for_forced_min_ <= 0) {
-    return;
-  }
-  // Reset windowed_min_rtt to the min of num_samples_for_forced_min_ samples.
-  if (forced_windowed_min_rtt_.IsZero() ||
-      rtt_sample <= forced_windowed_min_rtt_) {
-    forced_windowed_min_rtt_ = rtt_sample;
-    forced_windowed_min_rtt_time_ = now;
-  }
-  if (num_samples_for_forced_min_ == 1) {
-    windowed_min_rtt_.Reset(forced_windowed_min_rtt_,
-                            forced_windowed_min_rtt_time_);
-  }
-  --num_samples_for_forced_min_;
-}
-
 void RttStats::OnConnectionMigration() {
   latest_rtt_ = QuicTime::Delta::Zero();
   min_rtt_ = QuicTime::Delta::Zero();
   smoothed_rtt_ = QuicTime::Delta::Zero();
   mean_deviation_ = QuicTime::Delta::Zero();
   initial_rtt_us_ = kInitialRttMs * kNumMicrosPerMilli;
-  num_samples_for_forced_min_ = 0;
-  windowed_min_rtt_.Reset(QuicTime::Delta::Zero(), QuicTime::Zero());
 }
 
 }  // namespace net