Deciding best connection to schedule requests on based on cwnd and idle time

net/http/http_basic_stream.cc

Index: net/http/http_basic_stream.cc
===================================================================
--- net/http/http_basic_stream.cc	(revision 88319)
+++ net/http/http_basic_stream.cc	(working copy)
@@ -4,6 +4,7 @@
 
 #include "net/http/http_basic_stream.h"
 
+#include "base/metrics/histogram.h"
 #include "base/stringprintf.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
@@ -13,6 +14,12 @@
 #include "net/http/http_util.h"
 #include "net/socket/client_socket_handle.h"
 
+using base::Histogram;
+
+namespace {
+int g_socket_reuse_policy = -1;
+}
+
 namespace net {
 
 HttpBasicStream::HttpBasicStream(ClientSocketHandle* connection,
@@ -34,6 +41,7 @@
   request_info_ = request_info;
   parser_.reset(new HttpStreamParser(connection_.get(), request_info,
                                      read_buf_, net_log));
+  bytes_read_offset_ = connection_->socket()->NumBytesRead();
   return OK;
 }
 
@@ -50,6 +58,7 @@
   request_line_ = base::StringPrintf("%s %s HTTP/1.1\r\n",
                                      request_info_->method.c_str(),
                                      path.c_str());
+  response_ = response;
   return parser_->SendRequest(request_line_, headers, request_body, response,
                               callback);
 }
@@ -119,4 +128,44 @@
   return false;
 }
 
+void HttpBasicStream::LogNumRttVsBytesMetrics() const {
+  DCHECK_GE(g_socket_reuse_policy, 0);
+  DCHECK_LE(g_socket_reuse_policy, 3);
+
+  int64 total_bytes_read = connection_->socket()->NumBytesRead();
+  int64 bytes_received = total_bytes_read - bytes_read_offset_;
+  int64 num_kb = bytes_received / 1024;

[Mike Belshe, 2011/06/12 22:10:35]

Note:  for integers, division  truncates.  So for 0-1023 bytes, this will be 0.

[Gagan, 2011/06/13 03:52:47]

noted. 0 to 5120 bytes should all go in one bucket.

+  double rtt = connection_->socket()->GetConnectTimeMicros();
+  rtt /= 1000.0;
+
+  if (num_kb < 1024 && rtt > 0) {  // Ignore responses > 1MB
+    base::TimeDelta duration = base::Time::Now() -
+                               response_->request_time;
+    double num_rtt = static_cast<double>(duration.InMilliseconds()) / rtt;
+    int64 num_rtt_scaled = (4 * num_rtt);
+
+    const char* groups[] = { "last_accessed_socket", "warmest_socket",
+                             "warm_socket", "manual" };
+    int bucket = (num_kb / 5) * 5;

[Mike Belshe, 2011/06/12 22:10:35]

Again, integer math.  For 0 to 4KB this will be 0.  This is fine...

[Gagan, 2011/06/13 03:52:47]

+1.
For 0 - 5kb, in normal conditions, it should take 1 or 2 rtt's. 2 bucket
histogram should be able to record both.

+    const std::string histogram(StringPrintf("Net.Num_RTT_vs_KB_%s_%dKB",
+                                             groups[g_socket_reuse_policy],
+                                             bucket));
+    Histogram* counter = Histogram::FactoryGet(

[Mike Belshe, 2011/06/12 22:10:35]

Note, this is going to generate 600 different histograms :-)

(200 buckets and 3 combinations)

Also, you might want to use the FieldTrial::MakeName call.

[Gagan, 2011/06/13 03:52:47]

Agreed, hopefully in a binary it wont create all 200 depending on users browsing
pattern due to lazy creation.
I tried using it, but this was easier. I anyways had to append the bucket id.
Plus, to use FieldTrial::MakeName, i need the chosen group. I am passing the
enum value around, and not the chosen field trial group.

I can use FieldTrial::MakeName directly assuming that field trial groups are
also 0, 1, 2 ... in order of creation.

+        histogram, 0, 1000, 2, Histogram::kUmaTargetedHistogramFlag);
+    DCHECK_EQ(histogram, counter->histogram_name());
+    counter->Add(num_rtt_scaled);
+
+    LOG(ERROR) << request_line_

[Mike Belshe, 2011/06/12 22:10:35]

please remove this debugging error log.

[Gagan, 2011/06/13 03:52:47]

Will do so in the next round :) Please bear with me for one more round.
Logging is soo much better than debugging and tcpdump verification, though will
do so to be sure in the last round.

+               << "\nrtt = " << rtt << "\tnum_rtt = " << num_rtt
+               << "\tnum_kb = " << num_kb
+               << "\ttotal bytes = " << total_bytes_read
+               << "\thistogram = " << histogram;
+  }
+}
+
+// static
+void HttpBasicStream::SetSocketReusePolicy(int policy) {
+  g_socket_reuse_policy = policy;
+}
+
 }  // namespace net