Let alr dectector use a budged to detect underuse.

webrtc/modules/pacing/alr_detector.h

Index: webrtc/modules/pacing/alr_detector.h
diff --git a/webrtc/modules/pacing/alr_detector.h b/webrtc/modules/pacing/alr_detector.h
index 087e444da1e886d1d642ee1e4aa25d22bd99e046..197090cc16efcaac7c8ed8236cb3f817847300bc 100644
--- a/webrtc/modules/pacing/alr_detector.h
+++ b/webrtc/modules/pacing/alr_detector.h
@@ -14,6 +14,7 @@
 #include "webrtc/base/optional.h"
 #include "webrtc/base/rate_statistics.h"
 #include "webrtc/common_types.h"
+#include "webrtc/modules/pacing/interval_budget.h"
 #include "webrtc/modules/pacing/paced_sender.h"
 #include "webrtc/typedefs.h"
 
@@ -32,7 +33,7 @@ class AlrDetector {
   AlrDetector();
   ~AlrDetector();
 
-  void OnBytesSent(size_t bytes_sent, int64_t now_ms);
+  void OnBytesSent(size_t bytes_sent, int64_t delta_time_ms);
 
   // Set current estimated bandwidth.
   void SetEstimatedBitrate(int bitrate_bps);
@@ -44,8 +45,9 @@ class AlrDetector {
   struct AlrExperimentSettings {
     float pacing_factor = PacedSender::kDefaultPaceMultiplier;
     int64_t max_paced_queue_time = PacedSender::kMaxQueueLengthMs;
-    int alr_start_usage_percent = kDefaultAlrStartUsagePercent;
-    int alr_end_usage_percent = kDefaultAlrEndUsagePercent;
+    int alr_bandwidth_usage_percent = kDefaultAlrBandwidthUsagePercent;
+    int alr_start_budget_level_percent = kDefaultAlrStartBudgetLevelPercent;
+    int alr_stop_budget_level_percent = kDefaultAlrStopBudgetLevelPercent;
   };
   static rtc::Optional<AlrExperimentSettings> ParseAlrSettingsFromFieldTrial();
 
@@ -54,17 +56,20 @@ class AlrDetector {
   // below kAlrStartUsagePercent and ends when it raises above
   // kAlrEndUsagePercent. NOTE: This is intentionally conservative at the moment
   // until BW adjustments of application limited region is fine tuned.
-  static constexpr int kDefaultAlrStartUsagePercent = 60;
-  static constexpr int kDefaultAlrEndUsagePercent = 70;
+  static constexpr int kDefaultAlrBandwidthUsagePercent = 65;
+  static constexpr int kDefaultAlrStartBudgetLevelPercent = 20;
+  static constexpr int kDefaultAlrStopBudgetLevelPercent = -20;

[holmer, 2017/07/07 09:21:22]

-20% budget sounds to me like we're sending 20% too much? Isn't that way too
late to exit ALR?

[terelius, 2017/07/07 09:24:51]

How does the budget level relate to BW usage. Is there any hysteresis or will
any bandwidth usage < 65% eventually cause us to enter ALR, and any bandwidth >
65% exit it?

[tschumi, 2017/07/07 09:36:15]

The budged can reach from -500ms overuse to +500ms underused.
20% budget means 0.2 * 500ms = 100ms underused
-20% budget means -0.2 * 500ms = -100ms overused

I totally agree that the previous impl was way easier to understand.

[tschumi, 2017/07/07 09:36:15]

Is there any hysteresis => yes.
will any bandwidth usage < 65% eventually cause us to enter ALR, and any
bandwidth > 65% exit it => yes.

:)

The hysteresis is done with the budged level. (20%,-20%)
So the hysteresis is dependent on time and bandwidth diff.

[terelius, 2017/07/07 10:00:53]

So that means that there is no hysteresis based on bandwidth estimate, only how
long we are sending at 64% or 66%. This might be desired, but we could modify
the bandwidth_usage_percent_whenever we enter/exit ALR if we wanted to keep the
old 60-70% hysteresis.

   static const char* kScreenshareProbingBweExperimentName;
 
+  void UpdateBudgetWithElapsedTime(int64_t delta_time_ms);
+  void UpdateBudgetWithBytesSent(size_t bytes_sent);
+
  private:
-  int alr_start_usage_percent_;
-  int alr_end_usage_percent_;
-  RateStatistics rate_;
-  int estimated_bitrate_bps_;
+  int bandwidth_usage_percent_;

[holmer, 2017/07/07 09:21:22]

It's not entirely clear to me what bandwidth_usage_percent_ represents. I think
the old thresholds were easier to understand. Why do we have three thresholds
now, and not just a start and an end threshold?

[tschumi, 2017/07/07 09:36:15]

It represents:
 alr_budget = bandwidth_usage_percent_/ 100 * estimated_bitrate.

when we overuse the alr_budget we are not in alr.
when we underuse the alr_budget we are in alr.

+  int alr_start_budget_level_percent_;
+  int alr_stop_budget_level_percent_;
 
-  // Non-empty in ALR state.
+  IntervalBudget alr_budget_;
   rtc::Optional<int64_t> alr_started_time_ms_;
 };