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

chrome/browser/browser_main.cc

Index: chrome/browser/browser_main.cc
===================================================================
--- chrome/browser/browser_main.cc	(revision 88319)
+++ chrome/browser/browser_main.cc	(working copy)
@@ -100,6 +100,7 @@
 #include "net/base/cookie_monster.h"
 #include "net/base/net_module.h"
 #include "net/base/network_change_notifier.h"
+#include "net/http/http_basic_stream.h"
 #include "net/http/http_network_layer.h"
 #include "net/http/http_stream_factory.h"
 #include "net/socket/client_socket_pool_base.h"
@@ -207,6 +208,9 @@
 #include "views/touchui/touch_factory.h"
 #endif
 
+using net::internal::ClientSocketPoolBaseHelper;
+using net::HttpBasicStream;
+
 namespace net {
 class NetLog;
 }  // namespace net
@@ -474,6 +478,61 @@
   }
 }
 
+// If --bytes-read-vs-last-accessed-decay-coef is not specified, run an A/B
+// test for choosing the warmest socket.
+void BrowserMainParts::WarmConnectionFieldTrial() {
+  const CommandLine& command_line = parsed_command_line();
+  if (command_line.HasSwitch(switches::kTcpSocketEstimatedCwndDecayCoef)) {
+    std::string alpha_str = command_line.GetSwitchValueASCII(
+        switches::kTcpSocketEstimatedCwndDecayCoef);
+    double coef = 0;
+    base::StringToDouble(alpha_str, &coef);
+    ClientSocketPoolBaseHelper::set_tcp_socket_estimated_cwnd_decay_coef(
+        coef);
+    HttpBasicStream::set_warm_connection_field_trial_group("manual");
+    return;
+  }
+
+  const base::FieldTrial::Probability kWarmSocketDivisor = 100;
+  const base::FieldTrial::Probability kWarmSocketProbability = 33;  // 1% prob.

[Mike Belshe, 2011/06/09 16:08:52]

The comment is wrong here

[Gagan, 2011/06/09 19:49:26]

Done.

+
+  // After January 30, 2013 builds, it will always be in default group.
+  scoped_refptr<base::FieldTrial> warmest_socket_trial(
+      new base::FieldTrial(
+          "WarmSocketImpact", kWarmSocketDivisor, "last_accessed_socket",
+          2013, 1, 30));
+
+  // This (1000000) is the current default value.

[Mike Belshe, 2011/06/09 16:08:52]

I think the comment is wrong here too?

[Gagan, 2011/06/09 19:49:26]

Done.

+  const int last_accessed_socket = warmest_socket_trial->kDefaultGroupNumber;
+  const int warmest_socket = warmest_socket_trial->AppendGroup(
+      "warmest_socket", kWarmSocketProbability);
+  const int warm_socket = warmest_socket_trial->AppendGroup(
+      "warm_socket", kWarmSocketProbability);
+
+  const int warmest_socket_trial_group = warmest_socket_trial->group();
+
+  if (warmest_socket_trial_group == last_accessed_socket) {
+    ClientSocketPoolBaseHelper::set_tcp_socket_estimated_cwnd_decay_coef(

[Mike Belshe, 2011/06/09 16:08:52]

This seems like a strange place to set the policy.

I would have preferred that the ClientSocketPoolBaseHelper have:

enum {
   USE_WARMEST_SOCKET,
   USE_WARM_SOCKET,
   USE_LAST_SOCKET
} ClientSocketReusePolicy;

and then

SetSocketReusePolicy(USE_WARMEST_SOCKET)

would internally do:
   set_tcp_socket_estimated_cwnd_decay_coef(1000000)

In other words, the reader of code here in browser main shouldn't need to know
the guts of policy decisions deep inside the socket code.

[Gagan, 2011/06/09 19:49:26]

Done.

+        1000000);
+    HttpBasicStream::set_warm_connection_field_trial_group(
+        "last_accessed_socket");
+  } else if (warmest_socket_trial_group == warmest_socket) {
+    ClientSocketPoolBaseHelper::set_tcp_socket_estimated_cwnd_decay_coef(
+        1);
+    HttpBasicStream::set_warm_connection_field_trial_group(
+        "warmest_socket");
+  } else if (warmest_socket_trial_group == warm_socket) {
+    // 1.83841629 = decay of 20 KB per 5 mins.
+    ClientSocketPoolBaseHelper::set_tcp_socket_estimated_cwnd_decay_coef(
+        1.83841629);
+    HttpBasicStream::set_warm_connection_field_trial_group(
+        "warm_socket");
+  } else {
+    NOTREACHED() << "Invalid bytes_read_vs_last_accessed_alpha";
+  }
+}
+
+
 // If neither --enable-connect-backup-jobs or --disable-connect-backup-jobs is
 // specified, run an A/B test for automatically establishing backup TCP
 // connections when a certain timeout value is exceeded.
@@ -593,6 +652,7 @@
   prerender::ConfigurePrefetchAndPrerender(parsed_command_line());
   SpdyFieldTrial();
   ConnectBackupJobsFieldTrial();
+  WarmConnectionFieldTrial();
 }
 
 // -----------------------------------------------------------------------------