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finish cleanup in CongestionControl

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This commit is contained in:
Stephen Birarda 2015-07-29 13:57:05 -07:00
parent 613968f813
commit 7602c352d6
2 changed files with 42 additions and 36 deletions
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70
libraries/networking/src/udt/CongestionControl.cpp
View file

@ -112,68 +112,72 @@ void DefaultCC::onACK(SequenceNumber ackNum) {
}
void DefaultCC::onLoss(SequenceNumber rangeStart, SequenceNumber rangeEnd) {
//Slow Start stopped, if it hasn't yet
// stop the slow start if we haven't yet
if (_slowStart) {
_slowStart = false;
if (_receiveRate > 0) {
// Set the sending rate to the receiving rate.
_packetSendPeriod = USECS_PER_SECOND / _receiveRate;
return;
}
// If no receiving rate is observed, we have to compute the sending
// rate according to the current window size, and decrease it
// using the method below.
_packetSendPeriod = _congestionWindowSize / (_rtt + synInterval());
stopSlowStart();
}
_loss = true;
static const double INTER_PACKET_ARRIVAL_INCREASE = 1.125;
static const int MAX_DECREASES_PER_CONGESTION_EPOCH = 5;
// check if this NAK starts a new congestion period - this will be the case if the
// NAK received occured for a packet sent after the last decrease
if (rangeStart > _lastDecreaseMaxSeq) {
_lastDecreasePeriod = _packetSendPeriod;
static const double INTER_PACKET_ARRIVAL_INCREASE = 1.125;
_packetSendPeriod = ceil(_packetSendPeriod * INTER_PACKET_ARRIVAL_INCREASE);
// use EWMA to update the average number of NAKs per congestion
static const double NAK_EWMA_ALPHA = 0.125;
_avgNAKNum = (int)ceil(_avgNAKNum * (1 - NAK_EWMA_ALPHA) + _nakCount * NAK_EWMA_ALPHA);
// update the count of NAKs and count of decreases in this interval
_nakCount = 1;
_decCount = 1;
_decreaseCount = 1;
_lastDecreaseMaxSeq = _sendCurrSeqNum;
// remove global synchronization using randomization
srand((uint32_t)_lastDecreaseMaxSeq);
_decRandom = (int)ceil(_avgNAKNum * (double(rand()) / RAND_MAX));
// avoid synchronous rate decrease across connections using randomization
srand((unsigned) _lastDecreaseMaxSeq);
_randomDecreaseThreshold = (int) ceil(_avgNAKNum * (double(rand()) / RAND_MAX));
if (_decRandom < 1) {
_decRandom = 1;
if (_randomDecreaseThreshold < 1) {
_randomDecreaseThreshold = 1;
}
} else if ((_decCount ++ < 5) && (0 == (++ _nakCount % _decRandom))) {
// 0.875^5 = 0.51, rate should not be decreased by more than half within a congestion period
_packetSendPeriod = ceil(_packetSendPeriod * 1.125);
} else if ((_decreaseCount++ < MAX_DECREASES_PER_CONGESTION_EPOCH) && ((++_nakCount % _randomDecreaseThreshold) == 0)) {
// there have been fewer than MAX_DECREASES_PER_CONGESTION_EPOCH AND this NAK matches the random count at which we
// decided we would decrease the packet send period
_packetSendPeriod = ceil(_packetSendPeriod * INTER_PACKET_ARRIVAL_INCREASE);
_lastDecreaseMaxSeq = _sendCurrSeqNum;
}
}
void DefaultCC::onTimeout() {
if (_slowStart) {
_slowStart = false;
if (_receiveRate > 0) {
_packetSendPeriod = USECS_PER_SECOND / _receiveRate;
} else {
_packetSendPeriod = _congestionWindowSize / (_rtt + synInterval());
}
stopSlowStart();
} else {
/*
_lastDecPeriod = _packetSendPeriod;
_packetSendPeriod = ceil(_packetSendPeriod * 2);
_lastDecSeq = _lastAck;
*/
// UDT used to do the following on timeout if not in slow start - we should check if it could be helpful
// _lastDecreasePeriod = _packetSendPeriod;
// _packetSendPeriod = ceil(_packetSendPeriod * 2);
// this seems odd - the last ack they were setting _lastDecreaseMaxSeq to only applies to slow start
// _lastDecreaseMaxSeq = _slowStartLastAck;
}
}
void DefaultCC::stopSlowStart() {
_slowStart = false;
if (_receiveRate > 0) {
// Set the sending rate to the receiving rate.
_packetSendPeriod = USECS_PER_SECOND / _receiveRate;
return;
}
// If no receiving rate is observed, we have to compute the sending
// rate according to the current window size, and decrease it
// using the method below.
_packetSendPeriod = _congestionWindowSize / (_rtt + synInterval());
}

8
libraries/networking/src/udt/CongestionControl.h
View file

@ -103,16 +103,18 @@ public:
virtual void onTimeout();
private:
void stopSlowStart(); // stops the slow start on loss or timeout, if it's still on
std::chrono::high_resolution_clock::time_point _lastRCTime; // last rate increase time
bool _slowStart { true }; // if in slow start phase
SequenceNumber _slowStartLastAck; // last ACKed seq num
bool _loss { false }; // if loss happened since last rate increase
SequenceNumber _lastDecreaseMaxSeq; // max pkt seq num sent out when last decrease happened
double _lastDecreasePeriod { 1 }; // value of _packetSendPeriod when last decrease happened
int _nakCount { 0 }; // NAK counter
int _decRandom { 1 }; // random threshold on decrease by number of loss events
int _nakCount { 0 }; // number of NAKs in congestion epoch
int _randomDecreaseThreshold { 1 }; // random threshold on decrease by number of loss events
int _avgNAKNum { 0 }; // average number of NAKs per congestion
int _decCount { 0 }; // number of decreases in a congestion epoch
int _decreaseCount { 0 }; // number of decreases in a congestion epoch
};
}