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Modifying price-weighted curve #2947

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Modifying price-weighted curve #2947

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4 changes: 3 additions & 1 deletion cmd/livepeer/livepeer.go
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Expand Up @@ -130,7 +130,9 @@ func parseLivepeerConfig() starter.LivepeerConfig {
cfg.SelectRandWeight = flag.Float64("selectRandFreq", *cfg.SelectRandWeight, "Weight of the random factor in the orchestrator selection algorithm")
cfg.SelectStakeWeight = flag.Float64("selectStakeWeight", *cfg.SelectStakeWeight, "Weight of the stake factor in the orchestrator selection algorithm")
cfg.SelectPriceWeight = flag.Float64("selectPriceWeight", *cfg.SelectPriceWeight, "Weight of the price factor in the orchestrator selection algorithm")
cfg.SelectPriceExpFactor = flag.Float64("selectPriceExpFactor", *cfg.SelectPriceExpFactor, "Expresses how significant a small change of price is for the selection algorithm; default 100")
cfg.SelectPriceExpFactorA = flag.Float64("selectPriceExpFactorA", *cfg.SelectPriceExpFactorA, "Expresses how significant a small change of price is for the selection algorithm; default 0.001")
cfg.SelectPriceExpFactorB = flag.Float64("selectPriceExpFactorB", *cfg.SelectPriceExpFactorB, "Expresses how significant a small change of price is for the selection algorithm; default 20")
cfg.SelectPriceCenter = flag.Float64("selectPriceCenter", *cfg.SelectPriceCenter, "Centers the price weighted selection curve around this number, giving increasingly diminishing returns starting at that price point; default 150")
cfg.OrchPerfStatsURL = flag.String("orchPerfStatsUrl", *cfg.OrchPerfStatsURL, "URL of Orchestrator Performance Stream Tester")
cfg.Region = flag.String("region", *cfg.Region, "Region in which a broadcaster is deployed; used to select the region while using the orchestrator's performance stats")
cfg.MaxPricePerUnit = flag.Int("maxPricePerUnit", *cfg.MaxPricePerUnit, "The maximum transcoding price (in wei) per 'pixelsPerUnit' a broadcaster is willing to accept. If not set explicitly, broadcaster is willing to accept ANY price")
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24 changes: 16 additions & 8 deletions cmd/livepeer/starter/starter.go
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Expand Up @@ -92,7 +92,9 @@ type LivepeerConfig struct {
SelectRandWeight *float64
SelectStakeWeight *float64
SelectPriceWeight *float64
SelectPriceExpFactor *float64
SelectPriceExpFactorA *float64
SelectPriceExpFactorB *float64
SelectPriceCenter *float64
OrchPerfStatsURL *string
Region *string
MaxPricePerUnit *int
Expand Down Expand Up @@ -169,7 +171,9 @@ func DefaultLivepeerConfig() LivepeerConfig {
defaultSelectRandWeight := 0.3
defaultSelectStakeWeight := 0.7
defaultSelectPriceWeight := 0.0
defaultSelectPriceExpFactor := 100.0
defaultSelectPriceExpFactorA := 0.001
defaultSelectPriceExpFactorB := 20.0
defaultSelectPriceCenter := 150.0
defaultMaxSessions := strconv.Itoa(10)
defaultOrchPerfStatsURL := ""
defaultRegion := ""
Expand Down Expand Up @@ -257,7 +261,9 @@ func DefaultLivepeerConfig() LivepeerConfig {
SelectRandWeight: &defaultSelectRandWeight,
SelectStakeWeight: &defaultSelectStakeWeight,
SelectPriceWeight: &defaultSelectPriceWeight,
SelectPriceExpFactor: &defaultSelectPriceExpFactor,
SelectPriceExpFactorA: &defaultSelectPriceExpFactorA,
SelectPriceExpFactorB: &defaultSelectPriceExpFactorB,
SelectPriceCenter: &defaultSelectPriceCenter,
MaxSessions: &defaultMaxSessions,
OrchPerfStatsURL: &defaultOrchPerfStatsURL,
Region: &defaultRegion,
Expand Down Expand Up @@ -1498,11 +1504,13 @@ func createSelectionAlgorithm(cfg LivepeerConfig) (common.SelectionAlgorithm, er
*cfg.SelectStakeWeight, *cfg.SelectPriceWeight, *cfg.SelectRandWeight)
}
return server.ProbabilitySelectionAlgorithm{
MinPerfScore: *cfg.MinPerfScore,
StakeWeight: *cfg.SelectStakeWeight,
PriceWeight: *cfg.SelectPriceWeight,
RandWeight: *cfg.SelectRandWeight,
PriceExpFactor: *cfg.SelectPriceExpFactor,
MinPerfScore: *cfg.MinPerfScore,
StakeWeight: *cfg.SelectStakeWeight,
PriceWeight: *cfg.SelectPriceWeight,
RandWeight: *cfg.SelectRandWeight,
PriceExpFactorA: *cfg.SelectPriceExpFactorA,
PriceExpFactorB: *cfg.SelectPriceExpFactorB,
PriceCenter: *cfg.SelectPriceCenter,
}, nil
}

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8 changes: 6 additions & 2 deletions server/selection_algorithm.go
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Expand Up @@ -17,7 +17,9 @@ type ProbabilitySelectionAlgorithm struct {
PriceWeight float64
RandWeight float64

PriceExpFactor float64
PriceExpFactorA float64
PriceExpFactorB float64
PriceCenter float64
}

func (sa ProbabilitySelectionAlgorithm) Select(addrs []ethcommon.Address, stakes map[ethcommon.Address]int64, prices map[ethcommon.Address]float64, perfScores map[ethcommon.Address]float64) ethcommon.Address {
Expand Down Expand Up @@ -50,9 +52,11 @@ func (sa ProbabilitySelectionAlgorithm) filter(addrs []ethcommon.Address, scores

func (sa ProbabilitySelectionAlgorithm) calculateProbabilities(addrs []ethcommon.Address, stakes map[ethcommon.Address]int64, prices map[ethcommon.Address]float64) map[ethcommon.Address]float64 {
pricesNorm := map[ethcommon.Address]float64{}

// Normalize price-weighted selection according to a inverted sigmoid function
for _, addr := range addrs {
p := prices[addr]
pricesNorm[addr] = math.Exp(-1 * p / sa.PriceExpFactor)
pricesNorm[addr] = 1 / (1 + math.Pow(math.Exp(sa.PriceExpFactorA*(p-sa.PriceCenter)), sa.PriceExpFactorB))
}

var priceSum, stakeSum float64
Expand Down