Add the metric to record percentage improvement for parallel download.

content/browser/download/download_stats.cc

 // 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 "content/browser/download/download_stats.h"
 
 #include "base/macros.h"
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/sparse_histogram.h"
@@ skipping 800 matching lines @@
           "Download.ParallelizableDownloadBandwidth."
           "WithoutParallelRequests",
           bandwidth_without_parallel_streams);
     }
   }
 
   if (!uses_parallel_requests)
     return;
 
   if (bytes_downloaded_with_parallel_streams > 0) {
+    int64_t bandwidth_with_parallel_streams = CalculateBandwidthBytesPerSecond(
+        bytes_downloaded_with_parallel_streams, time_with_parallel_streams);
     RecordBandwidthMetric(
         "Download.ParallelizableDownloadBandwidth."
         "WithParallelRequestsMultipleStreams",
-        CalculateBandwidthBytesPerSecond(bytes_downloaded_with_parallel_streams,
-                                         time_with_parallel_streams));
+        bandwidth_with_parallel_streams);
+
+    if (bandwidth_without_parallel_streams) {
+      int bandwidth_ratio_percentage =
+          (100.0 * bandwidth_with_parallel_streams) /
+          bandwidth_without_parallel_streams;
+      UMA_HISTOGRAM_CUSTOM_COUNTS(
+          "Download.ParallelDownload.BandwidthRatioPercentage",
+          bandwidth_ratio_percentage, 0, 400, 101);
+      base::TimeDelta total_time =
+          time_with_parallel_streams + time_without_parallel_streams;
+      size_t total_size = bytes_downloaded_with_parallel_streams +
+                          bytes_downloaded_without_parallel_streams;
+      base::TimeDelta improved_time = base::TimeDelta::FromSecondsD(
+          static_cast<double>(total_size) / bandwidth_with_parallel_streams);
+      int time_ratio_percentage =

[qinmin, 2017/05/10 18:46:47]

This doesn't seem right.
When we say that parallel download improves the download time, shouldn't we
compare actual download time with the theoretical download time without parallel
requests?

So it should be total_time/(total_size/bandwidth_without_parallel_streams)?

[xingliu, 2017/05/10 20:08:06]

Done. Makes sense.

+          100.0 * improved_time.InSecondsF() / total_time.InSecondsF();
+      UMA_HISTOGRAM_CUSTOM_COUNTS(
+          "Download.ParallelDownload.TotalTimeRatioPercentage",
+          time_ratio_percentage, 0, 200, 101);
+    }
   }
 
   base::TimeDelta time_saved;
   if (bandwidth_without_parallel_streams > 0) {
     time_saved = base::TimeDelta::FromMilliseconds(
                      1000.0 * bytes_downloaded_with_parallel_streams /
                      bandwidth_without_parallel_streams) -
                  time_with_parallel_streams;
   }
   int kMillisecondsPerHour =
@@ skipping 98 matching lines @@
 }
 
 void RecordDownloadHttpResponseCode(int response_code) {
   UMA_HISTOGRAM_CUSTOM_ENUMERATION(
       "Download.HttpResponseCode",
       net::HttpUtil::MapStatusCodeForHistogram(response_code),
       net::HttpUtil::GetStatusCodesForHistogram());
 }
 
 }  // namespace content