Store network quality samples so we can compute percentiles.

net/base/network_quality_estimator.h

 // 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.
 
 #ifndef NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_
 #define NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_
 
 #include <stdint.h>
 
+#include <deque>
+
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
+#include "net/base/net_export.h"
 #include "net/base/network_change_notifier.h"
 
 namespace net {
 
-struct NetworkQuality;
+class NetworkQuality;
 
 // NetworkQualityEstimator provides network quality estimates (quality of the
 // full paths to all origins that have been connected to).
 // The estimates are based on the observed organic traffic.
 // A NetworkQualityEstimator instance is attached to URLRequestContexts and
 // observes the traffic of URLRequests spawned from the URLRequestContexts.
 // A single instance of NQE can be attached to multiple URLRequestContexts,
 // thereby increasing the single NQE instance's accuracy by providing more
 // observed traffic characteristics.
 class NET_EXPORT_PRIVATE NetworkQualityEstimator
     : public NetworkChangeNotifier::ConnectionTypeObserver {
  public:
   // Creates a new NetworkQualityEstimator.
   NetworkQualityEstimator();
 
   ~NetworkQualityEstimator() override;
 
-  // Returns an estimate of the current network quality.
-  NetworkQuality GetEstimate() const;
+  // Returns the peak estimates (fastest RTT and peak throughput) of the
+  // current network.
+  NetworkQuality GetPeakEstimate() const;
 
   // Notifies NetworkQualityEstimator that a response has been received.
-  // |prefilter_bytes_read| is the count of the bytes received prior to
-  // applying filters (e.g. decompression, SDCH) from request creation time
+  // |cumulative_prefilter_bytes_read| is the count of the bytes received prior
+  // to applying filters (e.g. decompression, SDCH) from request creation time
   // until now.
+  // |prefiltered_bytes_read| is the count of the bytes received prior
+  // to applying filters in the most recent read.
   void NotifyDataReceived(const URLRequest& request,
-                          int64_t prefilter_bytes_read);
+                          int64_t cumulative_prefilter_bytes_read,
+                          int64_t prefiltered_bytes_read);
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, StoreObservations);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
                            TestPeakKbpsFastestRTTUpdates);
+  FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, TestAddObservation);
   FRIEND_TEST_ALL_PREFIXES(URLRequestTestHTTP, NetworkQualityEstimator);
 
+  // Records the round trip time or throughput observation, along with the time
+  // the observation was made.
+  struct Observation {
+    Observation(int32_t value, base::TimeTicks timestamp);
+
+    ~Observation();
+
+    // Value of the observation.
+    const int32_t value;
+
+    // Time when the observation was taken.
+    const base::TimeTicks timestamp;
+  };
+
+  // Stores observations sorted by time.
+  class ObservationBuffer {
+   public:
+    ObservationBuffer();
+
+    ~ObservationBuffer();
+
+    // Adds an observation to the buffer. The oldest observation in the buffer
+    // will be evicted to make room if the buffer is already full.
+    void AddObservation(int32_t value);
+
+    // Returns the number of observations in this buffer.
+    size_t size() const;
+
+   private:
+    FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, StoreObservations);
+
+    // Maximum number of observations that can be held in the ObservationBuffer.
+    static const size_t kMaximumObservations;
+
+    // Holds observations sorted by time, with the oldest observation at the
+    // front of the queue.
+    std::deque<Observation> observations_;
+
+    DISALLOW_COPY_AND_ASSIGN(ObservationBuffer);
+  };
+
   // Tiny transfer sizes may give inaccurate throughput results.
   // Minimum size of the transfer over which the throughput is computed.
   static const int kMinTransferSizeInBytes = 10000;
 
   // Minimum duration (in microseconds) of the transfer over which the
   // throughput is computed.
   static const int kMinRequestDurationMicroseconds = 1000;
 
   // Construct a NetworkQualityEstimator instance allowing for test
   // configuration.
@@ skipping 13 matching lines @@
   const bool allow_localhost_requests_;
 
   // Time when last connection change was observed.
   base::TimeTicks last_connection_change_;
 
   // Last value passed to |OnConnectionTypeChanged|. This indicates the
   // current connection type.
   NetworkChangeNotifier::ConnectionType current_connection_type_;
 
   // Set if any network data has been received since last connectivity change.
-  bool bytes_read_since_last_connection_change_;
+  bool have_received_bytes_since_last_connection_change_;
 
   // Fastest round-trip-time (RTT) since last connectivity change. RTT measured
   // from URLRequest creation until first byte received.
-  base::TimeDelta fastest_RTT_since_last_connection_change_;
+  base::TimeDelta fastest_rtt_since_last_connection_change_;
 
-  // Rough measurement of downlink peak Kbps witnessed since last connectivity
+  // Rough measurement of downstream peak Kbps witnessed since last connectivity
   // change. The accuracy is decreased by ignoring these factors:
   // 1) Multiple URLRequests can occur concurrently.
   // 2) The transfer time includes at least one RTT while no bytes are read.
-  uint64_t peak_kbps_since_last_connection_change_;
+  int32_t peak_kbps_since_last_connection_change_;

[mmenke, 2015/06/11 15:11:01]

Should we really provide kilobits per second?  Seems like the first thing
everyone will do with it to actually use it is multiple it by 8.

For that matter, is there some reason not to just give bytes per second?  Seems
like that's the most directly usable by consumers.

[tbansal1, 2015/06/11 19:27:50]

It seems that (kilo|mega) bits per second is used everywhere in NCN. I tried to
be consistent with that. e.g., this is mbps:
https://code.google.com/p/chromium/codesearch#chromium/src/net/base/network_c...

this is kbps:
https://code.google.com/p/chromium/codesearch#chromium/src/net/base/network_c...

I wanted to operate in int32 regime (instead of doule), so used kbps. WDYT?

+
+  // Buffer that holds Kbps observations.
+  ObservationBuffer kbps_observations_;
+
+  // Buffer that holds RTT (in milliseconds) observations.
+  ObservationBuffer rtt_msec_observations_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkQualityEstimator);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_