routing: add proportional attempt cost

lnrpc/routerrpc/config.go

@@ -47,6 +47,7 @@ func DefaultConfig() *Config {
 		MinRouteProbability:   routing.DefaultMinRouteProbability,
 		PenaltyHalfLife:       routing.DefaultPenaltyHalfLife,
 		AttemptCost:           routing.DefaultAttemptCost.ToSatoshis(),
+		AttemptCostPPM:        routing.DefaultAttemptCostPPM,
 		MaxMcHistory:          routing.DefaultMaxMcHistory,
 	}
 
@@ -62,6 +63,7 @@ func GetRoutingConfig(cfg *Config) *RoutingConfig {
 		AprioriWeight:         cfg.AprioriWeight,
 		MinRouteProbability:   cfg.MinRouteProbability,
 		AttemptCost:           cfg.AttemptCost,
+		AttemptCostPPM:        cfg.AttemptCostPPM,
 		PenaltyHalfLife:       cfg.PenaltyHalfLife,
 		MaxMcHistory:          cfg.MaxMcHistory,
 	}

lnrpc/routerrpc/routing_config.go

@@ -32,7 +32,13 @@ type RoutingConfig struct {
 	// AttemptCost is the fixed virtual cost in path finding of a failed
 	// payment attempt. It is used to trade off potentially better routes
 	// against their probability of succeeding.
-	AttemptCost btcutil.Amount `long:"attemptcost" description:"The (virtual) cost in sats of a failed payment attempt"`
+	AttemptCost btcutil.Amount `long:"attemptcost" description:"The fixed (virtual) cost in sats of a failed payment attempt"`
+
+	// AttemptCostPPM is the proportional virtual cost in path finding of a
+	// failed payment attempt. It is used to trade off potentially better
+	// routes against their probability of succeeding. This parameter is
+	// expressed in parts per million of the total payment amount.
+	AttemptCostPPM int64 `long:"attemptcostppm" description:"The proportional (virtual) cost in sats of a failed payment attempt expressed in parts per million of the total payment amount"`
 
 	// MaxMcHistory defines the maximum number of payment results that
 	// are held on disk by mission control.