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add reno fallback for fast re-transmit

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This commit is contained in:
Stephen Birarda 2016-09-27 14:49:00 -07:00
parent 0b2e0a4167
commit 64a0239248
2 changed files with 27 additions and 10 deletions
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34
libraries/networking/src/udt/TCPVegasCC.cpp
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@ -83,7 +83,6 @@ bool TCPVegasCC::onACK(SequenceNumber ack, p_high_resolution_clock::time_point r
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;
auto it = _sentPacketTimes.find(ack + 1);
if (it != _sentPacketTimes.end()) {
@ -93,12 +92,27 @@ bool TCPVegasCC::onACK(SequenceNumber ack, p_high_resolution_clock::time_point r
auto sinceSend = duration_cast<microseconds>(now - it->second.first).count();
if (sinceSend >= estimatedTimeout) {
qDebug() << "FRT needed:" << sinceSend << estimatedTimeout;
// we've detected we need a fast re-transmit, send that back to the connection
_numACKSinceFastRetransmit = 0;
return true;
}
}
// if this is the 3rd duplicate ACK, we fallback to Reno's fast re-transmit
static const int RENO_FAST_RETRANSMIT_DUPLICATE_COUNT = 3;
if (ack == previousAck && ++_duplicateACKCount == RENO_FAST_RETRANSMIT_DUPLICATE_COUNT) {
// break out of slow start, we just hit loss
_slowStart = false;
// reset our fast re-transmit counters
_numACKSinceFastRetransmit = 0;
_duplicateACKCount = 0;
// return true so the caller knows we needed a fast re-transmit
return true;
}
} else {
_duplicateACKCount = 0;
}
_lastAck = ack;
@ -218,20 +232,22 @@ void TCPVegasCC::performRenoCongestionAvoidance(SequenceNumber ack) {
numAcked -= congestionWindow - _congestionWindowSize;
}
int preAIWindowSize = _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;
if (_ackAICount >= preAIWindowSize) {
_ackAICount = 0;
++_congestionWindowSize;
}
_acksBeforeAdditiveIncrease += numAcked;
if (_acksBeforeAdditiveIncrease >= _congestionWindowSize) {
int delta = _acksBeforeAdditiveIncrease / _congestionWindowSize;
_ackAICount += numAcked;
if (_ackAICount >= preAIWindowSize) {
int delta = _ackAICount / preAIWindowSize;
_acksBeforeAdditiveIncrease -= delta * _congestionWindowSize;
_acksBeforeAdditiveIncrease += delta;
_ackAICount -= delta * _congestionWindowSize;
_congestionWindowSize += delta;
}
}
}

3
libraries/networking/src/udt/TCPVegasCC.h
View file

@ -63,7 +63,8 @@ private:
int _numACKs { 0 }; // Holds the number of ACKs received during the last RTT
int _acksBeforeAdditiveIncrease { 0 };
int _ackAICount { 0 }; // Counter for number of ACKs received for Reno additive increase
int _duplicateACKCount { 0 }; // Counter for duplicate ACKs received
int _slowStartOddAdjust { 0 }; // Marker for every window adjustment every other RTT in slow-start