Cast: Increase UDP socket send buffer size

media/cast/net/cast_transport_sender_impl.cc

 // Copyright 2014 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 "media/cast/net/cast_transport_sender_impl.h"
 
 #include "base/single_thread_task_runner.h"
 #include "base/values.h"
 #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 {
 namespace cast {
 
 namespace {
 int LookupOptionWithDefault(const base::DictionaryValue& options,
                             const std::string& path,
                             int default_value) {
   int ret;
   if (options.GetInteger(path, &ret)) {
     return ret;
   } else {
     return default_value;
   }
 };
 
+// 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(
     net::NetLog* net_log,
     base::TickClock* clock,
     const net::IPEndPoint& remote_end_point,
     scoped_ptr<base::DictionaryValue> options,
     const CastTransportStatusCallback& status_callback,
     const BulkRawEventsCallback& raw_events_callback,
     base::TimeDelta raw_events_callback_interval,
@@ skipping 27 matching lines @@
     : clock_(clock),
       status_callback_(status_callback),
       transport_task_runner_(transport_task_runner),
       transport_(external_transport ? NULL
                                     : new UdpTransport(net_log,
                                                        transport_task_runner,
                                                        net::IPEndPoint(),
                                                        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_,
              external_transport ? external_transport : transport_.get(),
              transport_task_runner),
       raw_events_callback_(raw_events_callback),
       raw_events_callback_interval_(raw_events_callback_interval),
       last_byte_acked_for_audio_(0),
       weak_factory_(this) {
   DCHECK(clock_);
   if (!raw_events_callback_.is_null()) {
     DCHECK(raw_events_callback_interval > base::TimeDelta());
     event_subscriber_.reset(new SimpleEventSubscriber);
     logging_.AddRawEventSubscriber(event_subscriber_.get());
     transport_task_runner->PostDelayedTask(
         FROM_HERE,
         base::Bind(&CastTransportSenderImpl::SendRawEvents,
                    weak_factory_.GetWeakPtr()),
         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);
     }
     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) {
       wifi_options_autoreset_ = net::SetWifiOptions(wifi_options);

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

Do we restore the old wifi options when Cast streaming is shut down?  Why/why
not?  Seems like this could break or inhibit other Chromium features (especially
on ChromeOS).

     }
   }
 }
 
 CastTransportSenderImpl::~CastTransportSenderImpl() {
   if (event_subscriber_.get())
     logging_.RemoveRawEventSubscriber(event_subscriber_.get());
 }
 
 void CastTransportSenderImpl::InitializeAudio(
@@ skipping 265 matching lines @@
   // 2. Specifies a deduplication window. For video this would be the most
   //    recent RTT. For audio there is no deduplication.
   ResendPackets(ssrc,
                 cast_message.missing_frames_and_packets,
                 true,
                 dedup_info);
 }
 
 }  // namespace cast
 }  // namespace media