116 lines
2.9 KiB
C++
116 lines
2.9 KiB
C++
#include "./cubic.hpp"
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#include <cmath>
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#include <iostream>
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void CUBIC::updateReductionTimer(float time_delta) {
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const auto now {getTimeNow()};
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// only keep updating while the cca interaction is not too long ago
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// or simply when there are packets in flight
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// (you need space to resend timedout, which still use up pipe space)
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if (!_in_flight.empty() || now - _time_point_last_update <= getCurrentDelay()*4.f) {
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_time_since_reduction += time_delta;
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}
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}
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void CUBIC::resetReductionTimer(void) {
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_time_since_reduction = 0.f;
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}
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float CUBIC::getCWnD(void) const {
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const double K = cbrt(
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(_window_max * (1. - BETA)) / SCALING_CONSTANT
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);
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const double TK = _time_since_reduction - K;
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const double cwnd =
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SCALING_CONSTANT
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* TK * TK * TK // TK^3
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+ _window_max
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;
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#if 0
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std::cout
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<< "K:" << K
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<< " ts:" << time_since_reduction
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<< " TK:" << TK
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<< " cwnd:" << cwnd
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<< " rtt:" << getCurrentDelay()
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<< "\n"
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;
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#endif
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return std::max<float>(cwnd, 2.f * MAXIMUM_SEGMENT_SIZE);
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}
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void CUBIC::onCongestion(void) {
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// 8 is probably too much (800ms for 100ms rtt)
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if (_time_since_reduction >= getCurrentDelay()*4.f) {
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const auto tmp_old_tp = _time_since_reduction;
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const auto current_cwnd = getCWnD(); // TODO: remove, only used by logging?
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const auto current_wnd = getWindow(); // respects cwnd and fwnd
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resetReductionTimer();
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if (current_cwnd < _window_max) {
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// congestion before reaching the inflection point (prev window_max).
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// reduce to wnd*beta to be fair
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_window_max = current_wnd * BETA;
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} else {
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_window_max = current_wnd;
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}
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_window_max = std::max(_window_max, 2.0*MAXIMUM_SEGMENT_SIZE);
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#if 1
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std::cout << "----CONGESTION!"
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<< " cwnd:" << current_cwnd
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<< " wnd:" << current_wnd
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<< " cwnd_max:" << _window_max
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<< " pts:" << tmp_old_tp
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<< " rtt:" << getCurrentDelay()
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<< "\n"
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;
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#endif
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}
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}
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float CUBIC::getWindow(void) const {
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return std::min<float>(getCWnD(), FlowOnly::getWindow());
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}
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int64_t CUBIC::canSend(float time_delta) {
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const auto fspace_pkgs = FlowOnly::canSend(time_delta);
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updateReductionTimer(time_delta);
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if (fspace_pkgs == 0u) {
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std::cerr << "CUBIC: flow said 0\n";
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return 0u;
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}
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const auto window = getCWnD();
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int64_t cspace_bytes = window - _in_flight_bytes;
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if (cspace_bytes < MAXIMUM_SEGMENT_DATA_SIZE) {
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//std::cerr << "CUBIC: cspace < seg size\n";
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return 0u;
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}
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// also limit to max sendrate per tick, which is usually smaller than window
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// this is mostly to prevent spikes on empty windows
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const auto rate = window / getCurrentDelay();
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// we dont want this limit to fall below atleast 1 segment
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const int64_t max_bytes_per_tick = std::max<int64_t>(rate * time_delta + 0.5f, MAXIMUM_SEGMENT_SIZE);
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cspace_bytes = std::min<int64_t>(cspace_bytes, max_bytes_per_tick);
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// limit to whole packets
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int64_t cspace_pkgs = (cspace_bytes / MAXIMUM_SEGMENT_DATA_SIZE) * MAXIMUM_SEGMENT_DATA_SIZE;
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return std::min(cspace_pkgs, fspace_pkgs);
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}
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