eth/downloader: adaptive quality of service tuning

eth/downloader/peer.go

@@ -23,6 +23,8 @@ import (
 	"errors"
 	"fmt"
 	"math"
+	"sort"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -31,8 +33,8 @@ import (
 )
 
 const (
-	maxLackingHashes = 4096 // Maximum number of entries allowed on the list or lacking items
-	throughputImpact = 0.1  // The impact a single measurement has on a peer's final throughput value.
+	maxLackingHashes  = 4096 // Maximum number of entries allowed on the list or lacking items
+	measurementImpact = 0.1  // The impact a single measurement has on a peer's final throughput value.
 )
 
 // Hash and block fetchers belonging to eth/61 and below
@@ -68,6 +70,8 @@ type peer struct {
 	receiptThroughput float64 // Number of receipts measured to be retrievable per second
 	stateThroughput   float64 // Number of node data pieces measured to be retrievable per second
 
+	rtt time.Duration // Request round trip time to track responsiveness (QoS)
+
 	headerStarted  time.Time // Time instance when the last header fetch was started
 	blockStarted   time.Time // Time instance when the last block (body) fetch was started
 	receiptStarted time.Time // Time instance when the last receipt fetch was started
@@ -290,44 +294,47 @@ func (p *peer) setIdle(started time.Time, delivered int, throughput *float64, id
 		return
 	}
 	// Otherwise update the throughput with a new measurement
-	measured := float64(delivered) / (float64(time.Since(started)+1) / float64(time.Second)) // +1 (ns) to ensure non-zero divisor
-	*throughput = (1-throughputImpact)*(*throughput) + throughputImpact*measured
+	elapsed := time.Since(started) + 1 // +1 (ns) to ensure non-zero divisor
+	measured := float64(delivered) / (float64(elapsed) / float64(time.Second))
+
+	*throughput = (1-measurementImpact)*(*throughput) + measurementImpact*measured
+	p.rtt = time.Duration((1-measurementImpact)*float64(p.rtt) + measurementImpact*float64(elapsed))
 }
 
 // HeaderCapacity retrieves the peers header download allowance based on its
 // previously discovered throughput.
-func (p *peer) HeaderCapacity() int {
+func (p *peer) HeaderCapacity(targetRTT time.Duration) int {
 	p.lock.RLock()
 	defer p.lock.RUnlock()
 
-	return int(math.Max(1, math.Min(p.headerThroughput*float64(headerTargetRTT)/float64(time.Second), float64(MaxHeaderFetch))))
+	return int(math.Min(1+math.Max(1, p.headerThroughput*float64(targetRTT)/float64(time.Second)), float64(MaxHeaderFetch)))
 }
 
 // BlockCapacity retrieves the peers block download allowance based on its
 // previously discovered throughput.
-func (p *peer) BlockCapacity() int {
+func (p *peer) BlockCapacity(targetRTT time.Duration) int {
 	p.lock.RLock()
 	defer p.lock.RUnlock()
 
-	return int(math.Max(1, math.Min(p.blockThroughput*float64(blockTargetRTT)/float64(time.Second), float64(MaxBlockFetch))))
+	return int(math.Min(1+math.Max(1, p.blockThroughput*float64(targetRTT)/float64(time.Second)), float64(MaxBlockFetch)))
 }
 
 // ReceiptCapacity retrieves the peers receipt download allowance based on its
 // previously discovered throughput.
-func (p *peer) ReceiptCapacity() int {
+func (p *peer) ReceiptCapacity(targetRTT time.Duration) int {
 	p.lock.RLock()
 	defer p.lock.RUnlock()
 
-	return int(math.Max(1, math.Min(p.receiptThroughput*float64(receiptTargetRTT)/float64(time.Second), float64(MaxReceiptFetch))))
+	return int(math.Min(1+math.Max(1, p.receiptThroughput*float64(targetRTT)/float64(time.Second)), float64(MaxReceiptFetch)))
 }
 
 // NodeDataCapacity retrieves the peers state download allowance based on its
 // previously discovered throughput.
-func (p *peer) NodeDataCapacity() int {
+func (p *peer) NodeDataCapacity(targetRTT time.Duration) int {
 	p.lock.RLock()
 	defer p.lock.RUnlock()
 
-	return int(math.Max(1, math.Min(p.stateThroughput*float64(stateTargetRTT)/float64(time.Second), float64(MaxStateFetch))))
+	return int(math.Min(1+math.Max(1, p.stateThroughput*float64(targetRTT)/float64(time.Second)), float64(MaxStateFetch)))
 }
 
 // MarkLacking appends a new entity to the set of items (blocks, receipts, states)
@@ -361,13 +368,14 @@ func (p *peer) String() string {
 	p.lock.RLock()
 	defer p.lock.RUnlock()
 
-	return fmt.Sprintf("Peer %s [%s]", p.id,
-		fmt.Sprintf("headers %3.2f/s, ", p.headerThroughput)+
-			fmt.Sprintf("blocks %3.2f/s, ", p.blockThroughput)+
-			fmt.Sprintf("receipts %3.2f/s, ", p.receiptThroughput)+
-			fmt.Sprintf("states %3.2f/s, ", p.stateThroughput)+
-			fmt.Sprintf("lacking %4d", len(p.lacking)),
-	)
+	return fmt.Sprintf("Peer %s [%s]", p.id, strings.Join([]string{
+		fmt.Sprintf("hs %3.2f/s", p.headerThroughput),
+		fmt.Sprintf("bs %3.2f/s", p.blockThroughput),
+		fmt.Sprintf("rs %3.2f/s", p.receiptThroughput),
+		fmt.Sprintf("ss %3.2f/s", p.stateThroughput),
+		fmt.Sprintf("miss %4d", len(p.lacking)),
+		fmt.Sprintf("rtt %v", p.rtt),
+	}, ", "))
 }
 
 // peerSet represents the collection of active peer participating in the chain
@@ -402,6 +410,10 @@ func (ps *peerSet) Reset() {
 // average of all existing peers, to give it a realistic chance of being used
 // for data retrievals.
 func (ps *peerSet) Register(p *peer) error {
+	// Retrieve the current median RTT as a sane default
+	p.rtt = ps.medianRTT()
+
+	// Register the new peer with some meaningful defaults
 	ps.lock.Lock()
 	defer ps.lock.Unlock()
 
@@ -564,3 +576,34 @@ func (ps *peerSet) idlePeers(minProtocol, maxProtocol int, idleCheck func(*peer)
 	}
 	return idle, total
 }
+
+// medianRTT returns the median RTT of te peerset, considering only the tuning
+// peers if there are more peers available.
+func (ps *peerSet) medianRTT() time.Duration {
+	// Gather all the currnetly measured round trip times
+	ps.lock.RLock()
+	defer ps.lock.RUnlock()
+
+	rtts := make([]float64, 0, len(ps.peers))
+	for _, p := range ps.peers {
+		p.lock.RLock()
+		rtts = append(rtts, float64(p.rtt))
+		p.lock.RUnlock()
+	}
+	sort.Float64s(rtts)
+
+	median := rttMaxEstimate
+	if qosTuningPeers <= len(rtts) {
+		median = time.Duration(rtts[qosTuningPeers/2]) // Median of our tuning peers
+	} else if len(rtts) > 0 {
+		median = time.Duration(rtts[len(rtts)/2]) // Median of our connected peers (maintain even like this some baseline qos)
+	}
+	// Restrict the RTT into some QoS defaults, irrelevant of true RTT
+	if median < rttMinEstimate {
+		median = rttMinEstimate
+	}
+	if median > rttMaxEstimate {
+		median = rttMaxEstimate
+	}
+	return median
+}