Add FieldTrial to only send probes on OnMaxTotalAllocatedBitrate()

if currently sent bitrate is application-limited.

Bug: chromium:951299
Change-Id: Ibc1ebd74eaa4a019dc290c11b606796c5be21d0f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/131126
Commit-Queue: Konrad Hofbauer <hofbauer@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27539}

modules/congestion_controller/goog_cc/probe_controller.cc

@@ -73,6 +73,10 @@ constexpr char kBweRapidRecoveryExperiment[] =
 // Never probe higher than configured by OnMaxTotalAllocatedBitrate().
 constexpr char kCappedProbingFieldTrialName[] = "WebRTC-BweCappedProbing";
 
+// Only do allocation probing when in ALR (but not when network-limited).
+constexpr char kAllocProbingOnlyInAlrFieldTrialName[] =
+    "WebRTC-BweAllocProbingOnlyInAlr";
+
 void MaybeLogProbeClusterCreated(RtcEventLog* event_log,
                                  const ProbeClusterConfig& probe) {
   RTC_DCHECK(event_log);
@@ -121,6 +125,9 @@ ProbeController::ProbeController(const WebRtcKeyValueConfig* key_value_config,
       limit_probes_with_allocateable_rate_(
           key_value_config->Lookup(kCappedProbingFieldTrialName)
               .find("Disabled") != 0),
+      allocation_probing_only_in_alr_(
+          key_value_config->Lookup(kAllocProbingOnlyInAlrFieldTrialName)
+              .find("Enabled") == 0),
       event_log_(event_log),
       config_(ProbeControllerConfig(key_value_config)) {
   Reset(0);
@@ -181,11 +188,16 @@ std::vector<ProbeClusterConfig> ProbeController::SetBitrates(
 std::vector<ProbeClusterConfig> ProbeController::OnMaxTotalAllocatedBitrate(
     int64_t max_total_allocated_bitrate,
     int64_t at_time_ms) {
+  const bool in_alr = alr_start_time_ms_.has_value();
+  const bool allow_allocation_probe =
+      allocation_probing_only_in_alr_ ? in_alr : true;
+
   if (state_ == State::kProbingComplete &&
       max_total_allocated_bitrate != max_total_allocated_bitrate_ &&
       estimated_bitrate_bps_ != 0 &&
       (max_bitrate_bps_ <= 0 || estimated_bitrate_bps_ < max_bitrate_bps_) &&
-      estimated_bitrate_bps_ < max_total_allocated_bitrate) {
+      estimated_bitrate_bps_ < max_total_allocated_bitrate &&
+      allow_allocation_probe) {
     max_total_allocated_bitrate_ = max_total_allocated_bitrate;
 
     if (!config_.first_allocation_probe_scale)

modules/congestion_controller/goog_cc/probe_controller.h

@@ -134,6 +134,7 @@ class ProbeController {
 
   const bool in_rapid_recovery_experiment_;
   const bool limit_probes_with_allocateable_rate_;
+  const bool allocation_probing_only_in_alr_;
   // For WebRTC.BWE.MidCallProbing.* metric.
   bool mid_call_probing_waiting_for_result_;
   int64_t mid_call_probing_bitrate_bps_;

modules/congestion_controller/goog_cc/probe_controller_unittest.cc

@@ -95,6 +95,32 @@ TEST_F(ProbeControllerTest, InitiatesProbingOnMaxBitrateIncrease) {
   EXPECT_EQ(probes[0].target_data_rate.bps(), kMaxBitrateBps + 100);
 }
 
+TEST_F(ProbeControllerTest, ProbesOnMaxBitrateIncreaseOnlyWhenInAlr) {
+  test::ScopedFieldTrials trials("WebRTC-BweAllocProbingOnlyInAlr/Enabled/");
+  probe_controller_.reset(
+      new ProbeController(&field_trial_config_, &mock_rtc_event_log));
+  auto probes = probe_controller_->SetBitrates(kMinBitrateBps, kStartBitrateBps,
+                                               kMaxBitrateBps, NowMs());
+  probes = probe_controller_->SetEstimatedBitrate(kMaxBitrateBps - 1, NowMs());
+
+  // Wait long enough to time out exponential probing.
+  clock_.AdvanceTimeMilliseconds(kExponentialProbingTimeoutMs);
+  probes = probe_controller_->Process(NowMs());
+  EXPECT_EQ(probes.size(), 0u);
+
+  // Probe when in alr.
+  probe_controller_->SetAlrStartTimeMs(clock_.TimeInMilliseconds());
+  probes = probe_controller_->OnMaxTotalAllocatedBitrate(kMaxBitrateBps + 1,
+                                                         NowMs());
+  EXPECT_EQ(probes.size(), 2u);
+
+  // Do not probe when not in alr.
+  probe_controller_->SetAlrStartTimeMs(absl::nullopt);
+  probes = probe_controller_->OnMaxTotalAllocatedBitrate(kMaxBitrateBps + 2,
+                                                         NowMs());
+  EXPECT_TRUE(probes.empty());
+}
+
 TEST_F(ProbeControllerTest, InitiatesProbingOnMaxBitrateIncreaseAtMaxBitrate) {
   auto probes = probe_controller_->SetBitrates(kMinBitrateBps, kStartBitrateBps,
                                                kMaxBitrateBps, NowMs());