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initial re-implementation of reno cong avoid

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This commit is contained in:
Stephen Birarda 2016-09-27 14:40:50 -07:00
parent dbbdda3468
commit 0b2e0a4167
2 changed files with 88 additions and 39 deletions
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121
libraries/networking/src/udt/TCPVegasCC.cpp
View file

@ -27,6 +27,9 @@ TCPVegasCC::TCPVegasCC() {
bool TCPVegasCC::onACK(SequenceNumber ack, p_high_resolution_clock::time_point receiveTime) {
auto it = _sentPacketTimes.find(ack);
auto previousAck = _lastAck;
_lastAck = ack;
if (it != _sentPacketTimes.end()) {
// calculate the RTT (receive time - time ACK sent)
@ -52,8 +55,8 @@ bool TCPVegasCC::onACK(SequenceNumber ack, p_high_resolution_clock::time_point r
+ abs(lastRTT - _ewmaRTT)) / RTT_ESTIMATION_VARIANCE_ALPHA_NUMERATOR;
}
// add 1 to the number of RTT samples
++_numRTTs;
// add 1 to the number of ACKs during this RTT
++_numACKs;
// keep track of the lowest RTT during connection
_baseRTT = std::min(_baseRTT, lastRTT);
@ -78,7 +81,7 @@ bool TCPVegasCC::onACK(SequenceNumber ack, p_high_resolution_clock::time_point r
// after a previous fast re-transmit
++_numACKSinceFastRetransmit;
if (ack == _lastAck || _numACKSinceFastRetransmit < 3) {
if (ack == previousAck || _numACKSinceFastRetransmit < 3) {
// we may need to re-send ackNum + 1 if it has been more than our estimated timeout since it was sent
qDebug() << "FRT:" << (uint32_t) ack << (uint32_t) _lastAck << _numACKSinceFastRetransmit;
@ -98,6 +101,8 @@ bool TCPVegasCC::onACK(SequenceNumber ack, p_high_resolution_clock::time_point r
}
}
_lastAck = ack;
// ACK processed, no fast re-transmit required
return false;
}
@ -132,43 +137,43 @@ void TCPVegasCC::performCongestionAvoidance(udt::SequenceNumber ack) {
debug << "D:" << windowSizeDiff << "\n";
}
if (_numRTTs <= 2) {
qDebug() << "WE SHOULD BE USING RENO HERE" << _numRTTs;
}
if (_slowStart) {
if (windowSizeDiff > VEGAS_GAMMA_SEGMENTS) {
// we're going too fast - this breaks us out of slow start and we switch to linear increase/decrease
_slowStart = false;
int expectedWindowSize = _congestionWindowSize * _baseRTT / rtt;
_baseRTT = std::numeric_limits<int>::max();
if (wantDebug) {
debug << "EWS:" << expectedWindowSize;
}
// drop the congestion window size to the expected size, if smaller
_congestionWindowSize = std::min(_congestionWindowSize, expectedWindowSize + 1);
} else if (++_slowStartOddAdjust & 1) {
// we're in slow start and not going too fast
// this means that once every second RTT we perform exponential congestion window growth
_congestionWindowSize *= 2;
}
if (_numACKs <= 2) {
performRenoCongestionAvoidance(ack);
} else {
// this is the normal linear increase/decrease of the Vegas algorithm
// to figure out where the congestion window should be
if (windowSizeDiff > VEGAS_BETA_SEGMENTS) {
// the old congestion window was too fast (difference > beta)
// so reduce it to slow down
--_congestionWindowSize;
if (_slowStart) {
if (windowSizeDiff > VEGAS_GAMMA_SEGMENTS) {
// we're going too fast - this breaks us out of slow start and we switch to linear increase/decrease
_slowStart = false;
} else if (windowSizeDiff < VEGAS_ALPHA_SEGMENTS) {
// there aren't enough packets on the wire, add more to the congestion window
++_congestionWindowSize;
int expectedWindowSize = _congestionWindowSize * _baseRTT / rtt;
_baseRTT = std::numeric_limits<int>::max();
if (wantDebug) {
debug << "EWS:" << expectedWindowSize;
}
// drop the congestion window size to the expected size, if smaller
_congestionWindowSize = std::min(_congestionWindowSize, expectedWindowSize + 1);
} else if (++_slowStartOddAdjust & 1) {
// we're in slow start and not going too fast
// this means that once every second RTT we perform exponential congestion window growth
_congestionWindowSize *= 2;
}
} else {
// sending rate seems good, no congestion window adjustment
// this is the normal linear increase/decrease of the Vegas algorithm
// to figure out where the congestion window should be
if (windowSizeDiff > VEGAS_BETA_SEGMENTS) {
// the old congestion window was too fast (difference > beta)
// so reduce it to slow down
--_congestionWindowSize;
} else if (windowSizeDiff < VEGAS_ALPHA_SEGMENTS) {
// there aren't enough packets on the wire, add more to the congestion window
++_congestionWindowSize;
} else {
// sending rate seems good, no congestion window adjustment
}
}
}
@ -183,7 +188,7 @@ void TCPVegasCC::performCongestionAvoidance(udt::SequenceNumber ack) {
_currentMinRTT = std::numeric_limits<int>::max();
// reset our count of collected RTT samples
_numRTTs = 0;
_numACKs = 0;
if (wantDebug) {
debug << "CW:" << _congestionWindowSize << "SS:" << _slowStart << "\n";
@ -191,6 +196,46 @@ void TCPVegasCC::performCongestionAvoidance(udt::SequenceNumber ack) {
}
}
bool TCPVegasCC::isCongestionWindowLimited() {
if (_slowStart) {
return true;
} else {
return seqlen(_sendCurrSeqNum, _lastAck) < _congestionWindowSize;
}
}
void TCPVegasCC::performRenoCongestionAvoidance(SequenceNumber ack) {
if (!isCongestionWindowLimited()) {
return;
}
int numAcked = _numACKs;
// In "safe" area, increase.
if (_slowStart) {
int congestionWindow = std::min(_congestionWindowSize + numAcked, udt::MAX_PACKETS_IN_FLIGHT);
numAcked -= congestionWindow - _congestionWindowSize;
}
if (numAcked > 0) {
// In dangerous area, increase slowly.
// If credits accumulated at a higher w, apply them gently now.
if (_acksBeforeAdditiveIncrease >= _congestionWindowSize) {
_acksBeforeAdditiveIncrease = 0;
++_congestionWindowSize;
}
_acksBeforeAdditiveIncrease += numAcked;
if (_acksBeforeAdditiveIncrease >= _congestionWindowSize) {
int delta = _acksBeforeAdditiveIncrease / _congestionWindowSize;
_acksBeforeAdditiveIncrease -= delta * _congestionWindowSize;
_acksBeforeAdditiveIncrease += delta;
}
}
}
void TCPVegasCC::onPacketSent(int packetSize, SequenceNumber seqNum, p_high_resolution_clock::time_point timePoint) {
_sentPacketTimes[seqNum] = { timePoint, packetSize };

6
libraries/networking/src/udt/TCPVegasCC.h
View file

@ -41,6 +41,8 @@ protected:
virtual void performCongestionAvoidance(SequenceNumber ack);
virtual void setInitialSendSequenceNumber(SequenceNumber seqNum) override { _lastAck = seqNum - 1; }
private:
bool isCongestionWindowLimited();
void performRenoCongestionAvoidance(SequenceNumber ack);
using TimeSizePair = std::pair<p_high_resolution_clock::time_point, int>;
using PacketTimeList = std::map<SequenceNumber, TimeSizePair>;
@ -59,7 +61,9 @@ private:
int _ewmaRTT { -1 }; // Exponential weighted moving average RTT
int _rttVariance { 0 }; // Variance in collected RTT values
int _numRTTs { 0 }; // Holds the number of ACKs received during the last RTT
int _numACKs { 0 }; // Holds the number of ACKs received during the last RTT
int _acksBeforeAdditiveIncrease { 0 };
int _slowStartOddAdjust { 0 }; // Marker for every window adjustment every other RTT in slow-start