Cast: Increase UDP socket send buffer size

media/cast/net/cast_transport_sender_impl.cc

Index: media/cast/net/cast_transport_sender_impl.cc
diff --git a/media/cast/net/cast_transport_sender_impl.cc b/media/cast/net/cast_transport_sender_impl.cc
index 6c746f485bf4806be73bbf1c17e6a4927d2937b0..ac4772380075fc441e94770cd9265289fa064903 100644
--- a/media/cast/net/cast_transport_sender_impl.cc
+++ b/media/cast/net/cast_transport_sender_impl.cc
@@ -9,6 +9,7 @@
 #include "media/cast/net/cast_transport_config.h"
 #include "media/cast/net/cast_transport_defines.h"
 #include "media/cast/net/udp_transport.h"
+#include "net/base/net_errors.h"
 #include "net/base/net_util.h"
 
 namespace media {
@@ -26,6 +27,17 @@ int LookupOptionWithDefault(const base::DictionaryValue& options,
   }
 };
 
+// See header file for what these mean.
+const char kOptionPacerTargetBurstSize[] = "pacer_target_burst_size";
+const char kOptionPacerMaxBurstSize[] = "pacer_max_burst_size";
+const char kOptionDscp[] = "DSCP";
+const char kOptionWifiDisableScan[] = "disable_wifi_scan";
+const char kOptionWifiMediaStreamingMode[] = "media_streaming_mode";
+
+// 802.11n is the most commonly used network for cast streaming.
+// The maximum MAC level data unit is 64KB as defined in the standard.
+const int k802dot11nMaxAMPDUSize = 65536;

[miu, 2014/10/15 21:20:20]

This will lower the default setting on Linux.  Are you sure that's a good idea? 
What if all platforms were "maxed out" to 212992 instead?  It's possible
kernels/drivers would prefer a size larger than one data unit to help schedule
data transmission.  I'm just worried we're trying to outsmart the operating
system here.

+
 }  // namespace
 
 scoped_ptr<CastTransportSender> CastTransportSender::Create(
@@ -73,10 +85,10 @@ CastTransportSenderImpl::CastTransportSenderImpl(
                                                        remote_end_point,
                                                        status_callback)),
       pacer_(LookupOptionWithDefault(*options.get(),
-                                     "pacer_target_burst_size",
+                                     kOptionPacerTargetBurstSize,
                                      kTargetBurstSize),
              LookupOptionWithDefault(*options.get(),
-                                     "pacer_max_burst_size",
+                                     kOptionPacerMaxBurstSize,
                                      kMaxBurstSize),
              clock,
              &logging_,
@@ -98,7 +110,7 @@ CastTransportSenderImpl::CastTransportSenderImpl(
         raw_events_callback_interval);
   }
   if (transport_) {
-    if (options->HasKey("DSCP")) {
+    if (options->HasKey(kOptionDscp)) {
       // The default DSCP value for cast is AF41. Which gives it a higher
       // priority over other traffic.
       transport_->SetDscp(net::DSCP_AF41);
@@ -106,11 +118,22 @@ CastTransportSenderImpl::CastTransportSenderImpl(
     transport_->StartReceiving(
         base::Bind(&CastTransportSenderImpl::OnReceivedPacket,
                    weak_factory_.GetWeakPtr()));
+
+    // Socket send buffer size needs to be at least greater than one burst size
+    // and greater than MAC protocol data unit. We use the MPDU value of
+    // 802.11n since it is the most commonly used network for Cast Streaming.
+    int send_buffer_size = std::max<int32>(

[miu, 2014/10/15 21:20:21]

int, not int32 here.

[Alpha Left Google, 2014/10/15 23:07:26]

Done.

+        k802dot11nMaxAMPDUSize,
+        LookupOptionWithDefault(*options.get(), kOptionPacerMaxBurstSize,
+                                kMaxBurstSize) * kMaxIpPacketSize);
+    if (transport_->SetSendBufferSize(send_buffer_size) != net::OK) {

[miu, 2014/10/15 21:20:21]

Please make this a ctor argument to UdpTransport (line 85ish above), rather than
a separate method.  This issue/concept is specific to UdpTransport, and not any
other PacedSender implementation.

[Alpha Left Google, 2014/10/15 23:07:26]

Done.

+      VLOG(1) << "Cannot set send buffer size.";
+    }
     int wifi_options = 0;
-    if (options->HasKey("disable_wifi_scan")) {
+    if (options->HasKey(kOptionWifiDisableScan)) {
       wifi_options |= net::WIFI_OPTIONS_DISABLE_SCAN;
     }
-    if (options->HasKey("media_streaming_mode")) {
+    if (options->HasKey(kOptionWifiMediaStreamingMode)) {
       wifi_options |= net::WIFI_OPTIONS_MEDIA_STREAMING_MODE;
     }
     if (wifi_options) {