p2p: set timeout on FairMix in Backend,reduce timeout

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

eth/backend.go

@@ -62,6 +62,16 @@ import (
 	gethversion "github.com/ethereum/go-ethereum/version"
 )
 
+const (
+	// This is the fairness knob for the discovery mixer. When looking for peers, we'll
+	// wait this long for a single source of candidates before moving on and trying other
+	// sources. If this timeout expires, the source will be skipped in this round, but it
+	// will continue to fetch in the background and will have a chance with a new timeout
+	// in the next rounds, giving it overall more time but a proportionally smaller share.
+	// We expect a normal source to produce ~10 candidates per second.
+	discmixTimeout = 100 * time.Millisecond
+)
+
 // Config contains the configuration options of the ETH protocol.
 // Deprecated: use ethconfig.Config instead.
 type Config = ethconfig.Config
@@ -169,7 +179,7 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 		networkID:       networkID,
 		gasPrice:        config.Miner.GasPrice,
 		p2pServer:       stack.Server(),
-		discmix:         enode.NewFairMix(0),
+		discmix:         enode.NewFairMix(discmixTimeout),
 		shutdownTracker: shutdowncheck.NewShutdownTracker(chainDb),
 	}
 	bcVersion := rawdb.ReadDatabaseVersion(chainDb)

p2p/server.go

@@ -47,8 +47,9 @@ const (
 
 	// This is the fairness knob for the discovery mixer. When looking for peers, we'll
 	// wait this long for a single source of candidates before moving on and trying other
-	// sources.
+	// sources. Currently there is only one source at the Server level, so this has no effect.
-	discmixTimeout = 5 * time.Second
+	// Check the fairMox tineout in the Backend for the actual timeout.
+	discmixTimeout = 100 * time.Millisecond
 
 	// Connectivity defaults.
 	defaultMaxPendingPeers = 50