Use moving average to calculate tunnel creation success rate

libi2pd/Tunnel.cpp

@@ -332,8 +332,7 @@ namespace tunnel
 	Tunnels tunnels;
 
 	Tunnels::Tunnels (): m_IsRunning (false), m_Thread (nullptr),
-		m_NumSuccesiveTunnelCreations (0), m_NumFailedTunnelCreations (0)
-	{
+		m_TunnelCreationSuccessRate (TCSR_START_VALUE), m_TunnelCreationAttemptsNum(0) {
 	}
 
 	Tunnels::~Tunnels ()
@@ -630,7 +629,7 @@ namespace tunnel
 						}
 						// delete
 						it = pendingTunnels.erase (it);
-						m_NumFailedTunnelCreations++;
+						FailedTunnelCreation();
 					}
 					else
 						++it;
@@ -638,7 +637,7 @@ namespace tunnel
 				case eTunnelStateBuildFailed:
 					LogPrint (eLogDebug, "Tunnel: Pending build request ", it->first, " failed, deleted");
 					it = pendingTunnels.erase (it);
-					m_NumFailedTunnelCreations++;
+					FailedTunnelCreation();
 				break;
 				case eTunnelStateBuildReplyReceived:
 					// intermediate state, will be either established of build failed
@@ -647,7 +646,7 @@ namespace tunnel
 				default:
 					// success
 					it = pendingTunnels.erase (it);
-					m_NumSuccesiveTunnelCreations++;
+					SuccesiveTunnelCreation();
 			}
 		}
 	}

libi2pd/Tunnel.h

@@ -48,6 +48,9 @@ namespace tunnel
 	const size_t I2NP_TUNNEL_MESSAGE_SIZE = TUNNEL_DATA_MSG_SIZE + I2NP_HEADER_SIZE + 34; // reserved for alignment and NTCP 16 + 6 + 12
 	const size_t I2NP_TUNNEL_ENPOINT_MESSAGE_SIZE = 2*TUNNEL_DATA_MSG_SIZE + I2NP_HEADER_SIZE + TUNNEL_GATEWAY_HEADER_SIZE + 28; // reserved for alignment and NTCP 16 + 6 + 6
 
+	const double TCSR_SMOOTHING_CONSTANT = 0.0005; // smoothing constant in exponentially weighted moving average
+	const double TCSR_START_VALUE = 0.1; // start value of tunnel creation success rate
+
 	enum TunnelState
 	{
 		eTunnelStatePending,
@@ -267,8 +270,19 @@ namespace tunnel
 			i2p::util::MemoryPoolMt<I2NPMessageBuffer<I2NP_TUNNEL_ENPOINT_MESSAGE_SIZE> > m_I2NPTunnelEndpointMessagesMemoryPool;
 			i2p::util::MemoryPoolMt<I2NPMessageBuffer<I2NP_TUNNEL_MESSAGE_SIZE> > m_I2NPTunnelMessagesMemoryPool;
 
-			// some stats
-			int m_NumSuccesiveTunnelCreations, m_NumFailedTunnelCreations;
+			// Calculating of tunnel creation success rate
+			// A modified version of the EWMA algorithm, where alpha is increased at the beginning to accelerate similarity
+			void SuccesiveTunnelCreation() {
+				double alpha = TCSR_SMOOTHING_CONSTANT + (1 - TCSR_SMOOTHING_CONSTANT)/++m_TunnelCreationAttemptsNum;
+				m_TunnelCreationSuccessRate = alpha * 1 + (1 - alpha) * m_TunnelCreationSuccessRate;
+
+			};
+			void FailedTunnelCreation() {
+				double alpha = TCSR_SMOOTHING_CONSTANT + (1 - TCSR_SMOOTHING_CONSTANT)/++m_TunnelCreationAttemptsNum;
+				m_TunnelCreationSuccessRate = alpha * 0 + (1 - alpha) * m_TunnelCreationSuccessRate;
+			};
+			double m_TunnelCreationSuccessRate;
+			int m_TunnelCreationAttemptsNum;
 
 		public:
 
@@ -282,11 +296,7 @@ namespace tunnel
 			size_t CountOutboundTunnels() const;
 
 			int GetQueueSize () { return m_Queue.GetSize (); };
-			int GetTunnelCreationSuccessRate () const // in percents
-			{
-				int totalNum = m_NumSuccesiveTunnelCreations + m_NumFailedTunnelCreations;
-				return totalNum ? m_NumSuccesiveTunnelCreations*100/totalNum : 0;
-			}
+			int GetTunnelCreationSuccessRate () const { return std::round(m_TunnelCreationSuccessRate * 100); } // in percents
 	};
 
 	extern Tunnels tunnels;