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p2p/msgrate: be more lenient when calculating 'mean' #25653

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Sep 9, 2022
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p2p/msgrate: be more lenient when calculating 'mean' #25653

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22 changes: 9 additions & 13 deletions p2p/msgrate/msgrate.go
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Original file line number Diff line number Diff line change
Expand Up @@ -38,14 +38,6 @@ const measurementImpact = 0.1
// to fetch more than some local stable value.
const capacityOverestimation = 1.01

// qosTuningPeers is the number of best peers to tune round trip times based on.
// An Ethereum node doesn't need hundreds of connections to operate correctly,
// so instead of lowering our download speed to the median of potentially many
// bad nodes, we can target a smaller set of vey good nodes. At worse this will
// result in less nodes to sync from, but that's still better than some hogging
// the pipeline.
const qosTuningPeers = 5

// rttMinEstimate is the minimal round trip time to target requests for. Since
// every request entails a 2 way latency + bandwidth + serving database lookups,
// it should be generous enough to permit meaningful work to be done on top of
Expand Down Expand Up @@ -303,11 +295,15 @@ func (t *Trackers) medianRoundTrip() time.Duration {
}
sort.Float64s(rtts)

median := rttMaxEstimate
if qosTuningPeers <= len(rtts) {
median = time.Duration(rtts[qosTuningPeers/2]) // Median of our best few peers
} else if len(rtts) > 0 {
median = time.Duration(rtts[len(rtts)/2]) // Median of all out connected peers
var median time.Duration
switch len(rtts) {
case 0:
median = rttMaxEstimate
case 1:
median = time.Duration(rtts[0])
default:
idx := int(math.Sqrt(float64(len(rtts))))
median = time.Duration(rtts[idx])
}
// Restrict the RTT into some QoS defaults, irrelevant of true RTT
if median < rttMinEstimate {
Expand Down