vasilvv | 8ab2fda | 2024-09-12 08:48:43 -0700 | [diff] [blame] | 1 | // Copyright 2024 The Chromium Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #include "quiche/quic/moqt/moqt_bitrate_adjuster.h" |
| 6 | |
| 7 | #include <algorithm> |
| 8 | #include <cstdint> |
| 9 | |
| 10 | #include "quiche/quic/core/quic_bandwidth.h" |
| 11 | #include "quiche/quic/core/quic_time.h" |
| 12 | #include "quiche/common/platform/api/quiche_logging.h" |
| 13 | #include "quiche/web_transport/web_transport.h" |
| 14 | |
| 15 | namespace moqt { |
| 16 | |
| 17 | namespace { |
| 18 | |
| 19 | using ::quic::QuicBandwidth; |
| 20 | using ::quic::QuicTime; |
| 21 | using ::quic::QuicTimeDelta; |
| 22 | |
| 23 | // Whenever adjusting bitrate down, it is set to `kTargetBitrateMultiplier * |
| 24 | // bw`, where `bw` is typically windowed max bandwidth reported by BBR. The |
| 25 | // current value selected is a bit arbitrary; ideally, we would adjust down to |
| 26 | // the application data goodput (i.e. goodput excluding all of the framing |
| 27 | // overhead), but that would either require us knowing how to compute the |
| 28 | // framing overhead correctly, or implementing our own application-level goodput |
| 29 | // monitoring. |
| 30 | constexpr float kTargetBitrateMultiplier = 0.9f; |
| 31 | |
| 32 | // Avoid re-adjusting bitrate within N RTTs after adjusting it. Here, on a |
| 33 | // typical 20ms connection, 40 RTTs is 800ms. Cap the limit at 3000ms. |
| 34 | constexpr float kMinTimeBetweenAdjustmentsInRtts = 40; |
| 35 | constexpr QuicTimeDelta kMaxTimeBetweenAdjustments = |
| 36 | QuicTimeDelta::FromSeconds(3); |
| 37 | |
| 38 | } // namespace |
| 39 | |
| 40 | void MoqtBitrateAdjuster::OnObjectAckReceived( |
| 41 | uint64_t /*group_id*/, uint64_t /*object_id*/, |
| 42 | QuicTimeDelta delta_from_deadline) { |
| 43 | if (delta_from_deadline < QuicTimeDelta::Zero()) { |
| 44 | // While adjusting down upon the first sign of packets getting late might |
| 45 | // seem aggressive, note that: |
| 46 | // - By the time user occurs, this is already a user-visible issue (so, in |
| 47 | // some sense, this isn't aggressive enough). |
| 48 | // - The adjustment won't happen if we're already bellow `k * max_bw`, so |
| 49 | // if the delays are due to other factors like bufferbloat, the measured |
| 50 | // bandwidth will likely not result in a downwards adjustment. |
| 51 | AttemptAdjustingDown(); |
| 52 | } |
| 53 | } |
| 54 | |
| 55 | void MoqtBitrateAdjuster::AttemptAdjustingDown() { |
| 56 | webtransport::SessionStats stats = session_->GetSessionStats(); |
| 57 | |
| 58 | // Wait for a while after doing an adjustment. There are non-trivial costs to |
| 59 | // switching, so we should rate limit adjustments. |
| 60 | QuicTimeDelta adjustment_delay = |
| 61 | QuicTimeDelta(stats.smoothed_rtt * kMinTimeBetweenAdjustmentsInRtts); |
| 62 | adjustment_delay = std::min(adjustment_delay, kMaxTimeBetweenAdjustments); |
| 63 | QuicTime now = clock_->ApproximateNow(); |
| 64 | if (now - last_adjustment_time_ < adjustment_delay) { |
| 65 | return; |
| 66 | } |
| 67 | |
| 68 | // Only adjust downwards. |
| 69 | QuicBandwidth target_bandwidth = |
| 70 | kTargetBitrateMultiplier * |
| 71 | QuicBandwidth::FromBitsPerSecond(stats.estimated_send_rate_bps); |
| 72 | QuicBandwidth current_bandwidth = adjustable_->GetCurrentBitrate(); |
| 73 | if (current_bandwidth <= target_bandwidth) { |
| 74 | return; |
| 75 | } |
| 76 | |
| 77 | QUICHE_DLOG(INFO) << "Adjusting the bitrate from " << current_bandwidth |
| 78 | << " to " << target_bandwidth; |
| 79 | bool success = adjustable_->AdjustBitrate(target_bandwidth); |
| 80 | if (success) { |
| 81 | last_adjustment_time_ = now; |
| 82 | } |
| 83 | } |
| 84 | |
| 85 | void MoqtBitrateAdjuster::OnObjectAckSupportKnown(bool supported) { |
| 86 | QUICHE_DLOG_IF(WARNING, !supported) |
| 87 | << "OBJECT_ACK not supported; bitrate adjustments will not work."; |
| 88 | } |
| 89 | |
| 90 | } // namespace moqt |