From d6098cc52e35920e54c729e8f18a10df86cc546b Mon Sep 17 00:00:00 2001
From: Felix Lange <fjl@twurst.com>
Date: Wed, 27 Aug 2025 15:16:46 +0200
Subject: [PATCH] eth: optimize and add benchmark

---
 eth/handler.go      | 14 ++++-----
 eth/handler_test.go | 77 +++++++++++++++++++++++++++++++++------------
 2 files changed, 63 insertions(+), 28 deletions(-)

diff --git a/eth/handler.go b/eth/handler.go
index ee8a843516..ab308819bd 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -19,7 +19,6 @@ package eth
 import (
 	"cmp"
 	"errors"
-	"hash"
 	"hash/fnv"
 	"maps"
 	"math"
@@ -690,7 +689,6 @@ func (st *blockRangeState) currentRange() eth.BlockRangeUpdatePacket {
 
 type broadcastChoice struct {
 	self   enode.ID
-	hash   hash.Hash64
 	buffer map[*ethPeer]struct{}
 	tmp    []broadcastPeer
 }
@@ -703,7 +701,6 @@ type broadcastPeer struct {
 func newBroadcastChoice(self enode.ID) *broadcastChoice {
 	return &broadcastChoice{
 		self:   self,
-		hash:   fnv.New64(),
 		buffer: make(map[*ethPeer]struct{}),
 	}
 }
@@ -713,12 +710,13 @@ func newBroadcastChoice(self enode.ID) *broadcastChoice {
 func (bc *broadcastChoice) choosePeers(peers []*ethPeer, txSender common.Address) map[*ethPeer]struct{} {
 	// Compute scores.
 	bc.tmp = slices.Grow(bc.tmp[:0], len(peers))[:len(peers)]
+	hash := fnv.New64()
 	for i, peer := range peers {
-		bc.hash.Reset()
-		bc.hash.Write(bc.self[:])
-		bc.hash.Write(peer.Peer.Peer.ID().Bytes())
-		bc.hash.Write(txSender[:])
-		bc.tmp[i] = broadcastPeer{peer, bc.hash.Sum64()}
+		hash.Reset()
+		hash.Write(bc.self[:])
+		hash.Write(peer.Peer.Peer.ID().Bytes())
+		hash.Write(txSender[:])
+		bc.tmp[i] = broadcastPeer{peer, hash.Sum64()}
 	}
 
 	// Sort by score.
diff --git a/eth/handler_test.go b/eth/handler_test.go
index 218a167cc0..afd1d6077f 100644
--- a/eth/handler_test.go
+++ b/eth/handler_test.go
@@ -220,34 +220,18 @@ func (b *testHandler) close() {
 }
 
 func TestBroadcastChoice(t *testing.T) {
-	// Create choices.
 	self := enode.HexID("1111111111111111111111111111111111111111111111111111111111111111")
 	choice49 := newBroadcastChoice(self)
 	choice50 := newBroadcastChoice(self)
 
-	// Create test peers.
-	var (
-		rand  = rand.New(rand.NewSource(33))
-		peers = make([]*ethPeer, 50)
-	)
-	for i := range peers {
-		var id enode.ID
-		rand.Read(id[:])
-		p2pPeer := p2p.NewPeer(id, "test", nil)
-		ep := eth.NewPeer(eth.ETH69, p2pPeer, nil, nil)
-		peers[i] = &ethPeer{Peer: ep}
-	}
-	defer func() {
-		for _, p := range peers {
-			p.Close()
-		}
-	}()
-
-	// Create random tx sender addresses.
+	// Create test peers and random tx sender addresses.
+	rand := rand.New(rand.NewSource(33))
 	txsenders := make([]common.Address, 400)
 	for i := range txsenders {
 		rand.Read(txsenders[i][:])
 	}
+	peers := createTestPeers(rand, 50)
+	defer closePeers(peers)
 
 	// Evaluate choice49 first.
 	expectedCount := 7 // sqrt(49)
@@ -280,3 +264,56 @@ func TestBroadcastChoice(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkBroadcastChoice(b *testing.B) {
+	b.Run("50", func(b *testing.B) {
+		benchmarkBroadcastChoice(b, 50)
+	})
+	b.Run("200", func(b *testing.B) {
+		benchmarkBroadcastChoice(b, 200)
+	})
+	b.Run("500", func(b *testing.B) {
+		benchmarkBroadcastChoice(b, 500)
+	})
+}
+
+// This measures the overhead of sending one transaction to N peers.
+func benchmarkBroadcastChoice(b *testing.B, npeers int) {
+	rand := rand.New(rand.NewSource(33))
+	peers := createTestPeers(rand, npeers)
+	defer closePeers(peers)
+
+	txsenders := make([]common.Address, b.N)
+	for i := range txsenders {
+		rand.Read(txsenders[i][:])
+	}
+
+	self := enode.HexID("1111111111111111111111111111111111111111111111111111111111111111")
+	choice := newBroadcastChoice(self)
+
+	b.ResetTimer()
+	for i := range b.N {
+		set := choice.choosePeers(peers, txsenders[i])
+		if len(set) == 0 {
+			b.Fatal("empty result")
+		}
+	}
+}
+
+func createTestPeers(rand *rand.Rand, n int) []*ethPeer {
+	peers := make([]*ethPeer, n)
+	for i := range peers {
+		var id enode.ID
+		rand.Read(id[:])
+		p2pPeer := p2p.NewPeer(id, "test", nil)
+		ep := eth.NewPeer(eth.ETH69, p2pPeer, nil, nil)
+		peers[i] = &ethPeer{Peer: ep}
+	}
+	return peers
+}
+
+func closePeers(peers []*ethPeer) {
+	for _, p := range peers {
+		p.Close()
+	}
+}