Add a new finch experiment to control the system buffer size.

content/browser/renderer_host/p2p/socket_host_udp.h

 // Copyright (c) 2011 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 CONTENT_BROWSER_RENDERER_HOST_P2P_SOCKET_HOST_UDP_H_
 #define CONTENT_BROWSER_RENDERER_HOST_P2P_SOCKET_HOST_UDP_H_
 
 #include <deque>
 #include <set>
 #include <vector>
@@ skipping 25 matching lines @@
             const P2PHostAndIPEndPoint& remote_address) override;
   void Send(const net::IPEndPoint& to,
             const std::vector<char>& data,
             const rtc::PacketOptions& options,
             uint64 packet_id) override;
   P2PSocketHost* AcceptIncomingTcpConnection(
       const net::IPEndPoint& remote_address,
       int id) override;
   bool SetOption(P2PSocketOption option, int value) override;
 
+  // Helper functions to hijack upper 32 bits for latency calculation.
+  // PackCallRecord will return a "CallRecord".  A "CallRecord" has its lower 32
+  // bits as the lower 32 bits of packet id (without the random prefix) and its
+  // higher 32 bits as the lower 32 bits of tick count when the packet arrives
+  // at Send().
+  static uint64 PackCallRecord(const uint64 packet_id, const uint64 ticks_now);

[Alexei Svitkine (slow), 2014/11/04 15:17:50]

Nit: Usually primitive params aren't marked const.

[guoweis2, 2014/11/07 22:18:19]

Code removed.

+  // |ticks_diff| contains the difference between the time when
+  // |packed_call_record| is packed and |ticks_now|.
+  static void UnpackCallRecord(const uint64 packed_call_record,
+                               const uint64 random_socket_id_prefix,
+                               const uint64 ticks_now,
+                               uint64* packet_id,
+                               uint64* ticks_diff);
+
  private:
   friend class P2PSocketHostUdpTest;
 
   typedef std::set<net::IPEndPoint> ConnectedPeerSet;
 
   struct PendingPacket {
     PendingPacket(const net::IPEndPoint& to,
                   const std::vector<char>& content,
                   const rtc::PacketOptions& options,
                   uint64 id);
     ~PendingPacket();
     net::IPEndPoint to;
     scoped_refptr<net::IOBuffer> data;
     int size;
     rtc::PacketOptions packet_options;
     uint64 id;
   };
 
   void OnError();
 
+  void SetSendBufferSize();
+
   void DoRead();
   void OnRecv(int result);
   void HandleReadResult(int result);
 
   void DoSend(const PendingPacket& packet);
   void OnSend(uint64 packet_id, int result);
   void HandleSendResult(uint64 packet_id, int result);
 
   scoped_ptr<net::DatagramServerSocket> socket_;
   scoped_refptr<net::IOBuffer> recv_buffer_;
   net::IPEndPoint recv_address_;
 
   std::deque<PendingPacket> send_queue_;
   bool send_pending_;
   net::DiffServCodePoint last_dscp_;
 
+  // When the renderer sends the packet through IPC, an unique packet_id is
+  // stamped at each packet to allow tracing infrastructure to uniquely identify
+  // each packet. The packet id is always constructed as a random number at
+  // upper 32 bits and a sequence number starting from 0 at lower 32 bits. The
+  // packet id is also sent to socket::SendTo as a callback parameter in case
+  // when the socket can't send it synchronously. The callback only allows an
+  // int64 as a parameter. To allow us to track the latency across the
+  // asynchronous socket::SendTo, we are hijacking the higher 32 bits for
+  // latency calculation. The |random_socket_id_prefix| is kept here so we could
+  // reconstruct the correct packet id.
+  uint64 random_socket_id_prefix_;

[Alexei Svitkine (slow), 2014/11/04 15:17:50]

Nit: I think for new code, uint64_t is preferred (i.e. types with _t suffix).

[guoweis2, 2014/11/07 22:18:19]

Code removed.

+
   // Set of peer for which we have received STUN binding request or
   // response or relay allocation request or response.
   ConnectedPeerSet connected_peers_;
   P2PMessageThrottler* throttler_;
 
   DISALLOW_COPY_AND_ASSIGN(P2PSocketHostUdp);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_P2P_SOCKET_HOST_UDP_H_