mapper/batcher: add unit tests and benchmarks

Add comprehensive unit tests for the LockFreeBatcher covering AddNode/RemoveNode lifecycle, addToBatch routing (broadcast, targeted, full update), processBatchedChanges deduplication, cleanup of offline nodes, close/shutdown behavior, IsConnected state tracking, and connected map consistency. Add benchmarks for connection entry send, multi-channel send and broadcast, peer diff computation, sentPeers updates, addToBatch at various scales (10/100/1000 nodes), processBatchedChanges, broadcast delivery, IsConnected lookups, connected map enumeration, connection churn, and concurrent send+churn scenarios. Widen setupBatcherWithTestData to accept testing.TB so benchmarks can reuse the same database-backed test setup as unit tests.
2026-03-10 15:19:53 +00:00 · 2026-03-10 15:19:53 +00:00 · 21e02e5d1f
commit 21e02e5d1f
parent 2f94b80e70
3 changed files with 1732 additions and 1 deletions
--- a/hscontrol/mapper/batcher_bench_test.go
+++ b/hscontrol/mapper/batcher_bench_test.go
@ -0,0 +1,783 @@
+package mapper
+
+// Benchmarks for batcher components and full pipeline.
+//
+// Organized into three tiers:
+// - Component benchmarks: individual functions (connectionEntry.send, computePeerDiff, etc.)
+// - System benchmarks: batching mechanics (addToBatch, processBatchedChanges, broadcast)
+// - Full pipeline benchmarks: end-to-end with real DB (gated behind !testing.Short())
+//
+// All benchmarks use sub-benchmarks with 10/100/1000 node counts for scaling analysis.
+
+import (
+	"fmt"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/juanfont/headscale/hscontrol/types"
+	"github.com/juanfont/headscale/hscontrol/types/change"
+	"github.com/puzpuzpuz/xsync/v4"
+	"github.com/rs/zerolog"
+	"tailscale.com/tailcfg"
+)
+
+// ============================================================================
+// Component Benchmarks
+// ============================================================================
+
+// BenchmarkConnectionEntry_Send measures the throughput of sending a single
+// MapResponse through a connectionEntry with a buffered channel.
+func BenchmarkConnectionEntry_Send(b *testing.B) {
+	ch := make(chan *tailcfg.MapResponse, b.N+1)
+	entry := makeConnectionEntry("bench-conn", ch)
+	data := testMapResponse()
+
+	b.ResetTimer()
+
+	for range b.N {
+		_ = entry.send(data)
+	}
+}
+
+// BenchmarkMultiChannelSend measures broadcast throughput to multiple connections.
+func BenchmarkMultiChannelSend(b *testing.B) {
+	for _, connCount := range []int{1, 3, 10} {
+		b.Run(fmt.Sprintf("%dconn", connCount), func(b *testing.B) {
+			mc := newMultiChannelNodeConn(1, nil)
+
+			channels := make([]chan *tailcfg.MapResponse, connCount)
+			for i := range channels {
+				channels[i] = make(chan *tailcfg.MapResponse, b.N+1)
+				mc.addConnection(makeConnectionEntry(fmt.Sprintf("conn-%d", i), channels[i]))
+			}
+
+			data := testMapResponse()
+
+			b.ResetTimer()
+
+			for range b.N {
+				_ = mc.send(data)
+			}
+		})
+	}
+}
+
+// BenchmarkComputePeerDiff measures the cost of computing peer diffs at scale.
+func BenchmarkComputePeerDiff(b *testing.B) {
+	for _, peerCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dpeers", peerCount), func(b *testing.B) {
+			mc := newMultiChannelNodeConn(1, nil)
+
+			// Populate tracked peers: 1..peerCount
+			for i := 1; i <= peerCount; i++ {
+				mc.lastSentPeers.Store(tailcfg.NodeID(i), struct{}{})
+			}
+
+			// Current peers: remove ~10% (every 10th peer is missing)
+			current := make([]tailcfg.NodeID, 0, peerCount)
+			for i := 1; i <= peerCount; i++ {
+				if i%10 != 0 {
+					current = append(current, tailcfg.NodeID(i))
+				}
+			}
+
+			b.ResetTimer()
+
+			for range b.N {
+				_ = mc.computePeerDiff(current)
+			}
+		})
+	}
+}
+
+// BenchmarkUpdateSentPeers measures the cost of updating peer tracking state.
+func BenchmarkUpdateSentPeers(b *testing.B) {
+	for _, peerCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dpeers_full", peerCount), func(b *testing.B) {
+			mc := newMultiChannelNodeConn(1, nil)
+
+			// Pre-build response with full peer list
+			peerIDs := make([]tailcfg.NodeID, peerCount)
+			for i := range peerIDs {
+				peerIDs[i] = tailcfg.NodeID(i + 1)
+			}
+
+			resp := testMapResponseWithPeers(peerIDs...)
+
+			b.ResetTimer()
+
+			for range b.N {
+				mc.updateSentPeers(resp)
+			}
+		})
+
+		b.Run(fmt.Sprintf("%dpeers_incremental", peerCount), func(b *testing.B) {
+			mc := newMultiChannelNodeConn(1, nil)
+
+			// Pre-populate with existing peers
+			for i := 1; i <= peerCount; i++ {
+				mc.lastSentPeers.Store(tailcfg.NodeID(i), struct{}{})
+			}
+
+			// Build incremental response: add 10% new peers
+			addCount := peerCount / 10
+			if addCount == 0 {
+				addCount = 1
+			}
+
+			resp := testMapResponse()
+
+			resp.PeersChanged = make([]*tailcfg.Node, addCount)
+			for i := range addCount {
+				resp.PeersChanged[i] = &tailcfg.Node{ID: tailcfg.NodeID(peerCount + i + 1)}
+			}
+
+			b.ResetTimer()
+
+			for range b.N {
+				mc.updateSentPeers(resp)
+			}
+		})
+	}
+}
+
+// ============================================================================
+// System Benchmarks (no DB, batcher mechanics only)
+// ============================================================================
+
+// benchBatcher creates a lightweight batcher for benchmarks. Unlike the test
+// helper, it doesn't register cleanup and suppresses logging.
+func benchBatcher(nodeCount, bufferSize int) (*LockFreeBatcher, map[types.NodeID]chan *tailcfg.MapResponse) {
+	b := &LockFreeBatcher{
+		tick:           time.NewTicker(1 * time.Hour), // never fires during bench
+		workers:        4,
+		workCh:         make(chan work, 4*200),
+		nodes:          xsync.NewMap[types.NodeID, *multiChannelNodeConn](),
+		connected:      xsync.NewMap[types.NodeID, *time.Time](),
+		pendingChanges: xsync.NewMap[types.NodeID, []change.Change](),
+		done:           make(chan struct{}),
+	}
+
+	channels := make(map[types.NodeID]chan *tailcfg.MapResponse, nodeCount)
+	for i := 1; i <= nodeCount; i++ {
+		id := types.NodeID(i) //nolint:gosec // benchmark with small controlled values
+		mc := newMultiChannelNodeConn(id, nil)
+		ch := make(chan *tailcfg.MapResponse, bufferSize)
+		entry := &connectionEntry{
+			id:      fmt.Sprintf("conn-%d", i),
+			c:       ch,
+			version: tailcfg.CapabilityVersion(100),
+			created: time.Now(),
+		}
+		entry.lastUsed.Store(time.Now().Unix())
+		mc.addConnection(entry)
+		b.nodes.Store(id, mc)
+		b.connected.Store(id, nil)
+		channels[id] = ch
+	}
+
+	b.totalNodes.Store(int64(nodeCount))
+
+	return b, channels
+}
+
+// BenchmarkAddToBatch_Broadcast measures the cost of broadcasting a change
+// to all nodes via addToBatch (no worker processing, just queuing).
+func BenchmarkAddToBatch_Broadcast(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, _ := benchBatcher(nodeCount, 10)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			ch := change.DERPMap()
+
+			b.ResetTimer()
+
+			for range b.N {
+				batcher.addToBatch(ch)
+				// Clear pending to avoid unbounded growth
+				batcher.pendingChanges.Range(func(id types.NodeID, _ []change.Change) bool {
+					batcher.pendingChanges.Delete(id)
+					return true
+				})
+			}
+		})
+	}
+}
+
+// BenchmarkAddToBatch_Targeted measures the cost of adding a targeted change
+// to a single node.
+func BenchmarkAddToBatch_Targeted(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, _ := benchBatcher(nodeCount, 10)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			b.ResetTimer()
+
+			for i := range b.N {
+				targetID := types.NodeID(1 + (i % nodeCount)) //nolint:gosec // benchmark
+				ch := change.Change{
+					Reason:     "bench-targeted",
+					TargetNode: targetID,
+					PeerPatches: []*tailcfg.PeerChange{
+						{NodeID: tailcfg.NodeID(targetID)}, //nolint:gosec // benchmark
+					},
+				}
+				batcher.addToBatch(ch)
+				// Clear pending periodically to avoid growth
+				if i%100 == 99 {
+					batcher.pendingChanges.Range(func(id types.NodeID, _ []change.Change) bool {
+						batcher.pendingChanges.Delete(id)
+						return true
+					})
+				}
+			}
+		})
+	}
+}
+
+// BenchmarkAddToBatch_FullUpdate measures the cost of a FullUpdate broadcast.
+func BenchmarkAddToBatch_FullUpdate(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, _ := benchBatcher(nodeCount, 10)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			b.ResetTimer()
+
+			for range b.N {
+				batcher.addToBatch(change.FullUpdate())
+			}
+		})
+	}
+}
+
+// BenchmarkProcessBatchedChanges measures the cost of moving pending changes
+// to the work queue.
+func BenchmarkProcessBatchedChanges(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dpending", nodeCount), func(b *testing.B) {
+			batcher, _ := benchBatcher(nodeCount, 10)
+			// Use a very large work channel to avoid blocking
+			batcher.workCh = make(chan work, nodeCount*b.N+1)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			b.ResetTimer()
+
+			for range b.N {
+				b.StopTimer()
+				// Seed pending changes
+				for i := 1; i <= nodeCount; i++ {
+					batcher.pendingChanges.Store(types.NodeID(i), []change.Change{change.DERPMap()}) //nolint:gosec // benchmark
+				}
+
+				b.StartTimer()
+
+				batcher.processBatchedChanges()
+			}
+		})
+	}
+}
+
+// BenchmarkBroadcastToN measures end-to-end broadcast: addToBatch + processBatchedChanges
+// to N nodes. Does NOT include worker processing (MapResponse generation).
+func BenchmarkBroadcastToN(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, _ := benchBatcher(nodeCount, 10)
+			batcher.workCh = make(chan work, nodeCount*b.N+1)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			ch := change.DERPMap()
+
+			b.ResetTimer()
+
+			for range b.N {
+				batcher.addToBatch(ch)
+				batcher.processBatchedChanges()
+			}
+		})
+	}
+}
+
+// BenchmarkMultiChannelBroadcast measures the cost of sending a MapResponse
+// to N nodes each with varying connection counts.
+func BenchmarkMultiChannelBroadcast(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, _ := benchBatcher(nodeCount, b.N+1)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			// Add extra connections to every 3rd node
+			for i := 1; i <= nodeCount; i++ {
+				if i%3 == 0 {
+					if mc, ok := batcher.nodes.Load(types.NodeID(i)); ok { //nolint:gosec // benchmark
+						for j := range 2 {
+							ch := make(chan *tailcfg.MapResponse, b.N+1)
+							entry := &connectionEntry{
+								id:      fmt.Sprintf("extra-%d-%d", i, j),
+								c:       ch,
+								version: tailcfg.CapabilityVersion(100),
+								created: time.Now(),
+							}
+							entry.lastUsed.Store(time.Now().Unix())
+							mc.addConnection(entry)
+						}
+					}
+				}
+			}
+
+			data := testMapResponse()
+
+			b.ResetTimer()
+
+			for range b.N {
+				batcher.nodes.Range(func(_ types.NodeID, mc *multiChannelNodeConn) bool {
+					_ = mc.send(data)
+					return true
+				})
+			}
+		})
+	}
+}
+
+// BenchmarkConcurrentAddToBatch measures addToBatch throughput under
+// concurrent access from multiple goroutines.
+func BenchmarkConcurrentAddToBatch(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, _ := benchBatcher(nodeCount, 10)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			// Background goroutine to drain pending periodically
+			drainDone := make(chan struct{})
+
+			go func() {
+				defer close(drainDone)
+
+				for {
+					select {
+					case <-batcher.done:
+						return
+					default:
+						batcher.pendingChanges.Range(func(id types.NodeID, _ []change.Change) bool {
+							batcher.pendingChanges.Delete(id)
+							return true
+						})
+						time.Sleep(time.Millisecond) //nolint:forbidigo // benchmark drain loop
+					}
+				}
+			}()
+
+			ch := change.DERPMap()
+
+			b.ResetTimer()
+			b.RunParallel(func(pb *testing.PB) {
+				for pb.Next() {
+					batcher.addToBatch(ch)
+				}
+			})
+			b.StopTimer()
+
+			// Cleanup
+			close(batcher.done)
+			<-drainDone
+			// Re-open done so the defer doesn't double-close
+			batcher.done = make(chan struct{})
+		})
+	}
+}
+
+// BenchmarkIsConnected measures the read throughput of IsConnected checks.
+func BenchmarkIsConnected(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, _ := benchBatcher(nodeCount, 1)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			b.ResetTimer()
+
+			for i := range b.N {
+				id := types.NodeID(1 + (i % nodeCount)) //nolint:gosec // benchmark
+				_ = batcher.IsConnected(id)
+			}
+		})
+	}
+}
+
+// BenchmarkConnectedMap measures the cost of building the full connected map.
+func BenchmarkConnectedMap(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, _ := benchBatcher(nodeCount, 1)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			// Disconnect 10% of nodes for a realistic mix
+			for i := 1; i <= nodeCount; i++ {
+				if i%10 == 0 {
+					now := time.Now()
+					batcher.connected.Store(types.NodeID(i), &now) //nolint:gosec // benchmark
+				}
+			}
+
+			b.ResetTimer()
+
+			for range b.N {
+				_ = batcher.ConnectedMap()
+			}
+		})
+	}
+}
+
+// BenchmarkConnectionChurn measures the cost of add/remove connection cycling
+// which simulates client reconnection patterns.
+func BenchmarkConnectionChurn(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100, 1000} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, channels := benchBatcher(nodeCount, 10)
+
+			defer func() {
+				close(batcher.done)
+				batcher.tick.Stop()
+			}()
+
+			b.ResetTimer()
+
+			for i := range b.N {
+				id := types.NodeID(1 + (i % nodeCount)) //nolint:gosec // benchmark
+
+				mc, ok := batcher.nodes.Load(id)
+				if !ok {
+					continue
+				}
+
+				// Remove old connection
+				oldCh := channels[id]
+				mc.removeConnectionByChannel(oldCh)
+
+				// Add new connection
+				newCh := make(chan *tailcfg.MapResponse, 10)
+				entry := &connectionEntry{
+					id:      fmt.Sprintf("churn-%d", i),
+					c:       newCh,
+					version: tailcfg.CapabilityVersion(100),
+					created: time.Now(),
+				}
+				entry.lastUsed.Store(time.Now().Unix())
+				mc.addConnection(entry)
+
+				channels[id] = newCh
+			}
+		})
+	}
+}
+
+// BenchmarkConcurrentSendAndChurn measures the combined cost of sends happening
+// concurrently with connection churn - the hot path in production.
+func BenchmarkConcurrentSendAndChurn(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			batcher, channels := benchBatcher(nodeCount, 100)
+
+			var mu sync.Mutex // protect channels map
+
+			stopChurn := make(chan struct{})
+			defer close(stopChurn)
+
+			// Background churn on 10% of nodes
+			go func() {
+				i := 0
+
+				for {
+					select {
+					case <-stopChurn:
+						return
+					default:
+						id := types.NodeID(1 + (i % nodeCount)) //nolint:gosec // benchmark
+						if i%10 == 0 {                          // only churn 10%
+							mc, ok := batcher.nodes.Load(id)
+							if ok {
+								mu.Lock()
+								oldCh := channels[id]
+								mu.Unlock()
+								mc.removeConnectionByChannel(oldCh)
+
+								newCh := make(chan *tailcfg.MapResponse, 100)
+								entry := &connectionEntry{
+									id:      fmt.Sprintf("churn-%d", i),
+									c:       newCh,
+									version: tailcfg.CapabilityVersion(100),
+									created: time.Now(),
+								}
+								entry.lastUsed.Store(time.Now().Unix())
+								mc.addConnection(entry)
+								mu.Lock()
+								channels[id] = newCh
+								mu.Unlock()
+							}
+						}
+
+						i++
+					}
+				}
+			}()
+
+			data := testMapResponse()
+
+			b.ResetTimer()
+
+			for range b.N {
+				batcher.nodes.Range(func(_ types.NodeID, mc *multiChannelNodeConn) bool {
+					_ = mc.send(data)
+					return true
+				})
+			}
+		})
+	}
+}
+
+// ============================================================================
+// Full Pipeline Benchmarks (with DB)
+// ============================================================================
+
+// BenchmarkAddNode measures the cost of adding nodes to the batcher,
+// including initial MapResponse generation from a real database.
+func BenchmarkAddNode(b *testing.B) {
+	if testing.Short() {
+		b.Skip("skipping full pipeline benchmark in short mode")
+	}
+
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			testData, cleanup := setupBatcherWithTestData(b, NewBatcherAndMapper, 1, nodeCount, LARGE_BUFFER_SIZE)
+			defer cleanup()
+
+			batcher := testData.Batcher
+			allNodes := testData.Nodes
+
+			// Start consumers
+			for i := range allNodes {
+				allNodes[i].start()
+			}
+
+			defer func() {
+				for i := range allNodes {
+					allNodes[i].cleanup()
+				}
+			}()
+
+			b.ResetTimer()
+
+			for range b.N {
+				// Connect all nodes (measuring AddNode cost)
+				for i := range allNodes {
+					node := &allNodes[i]
+					_ = batcher.AddNode(node.n.ID, node.ch, tailcfg.CapabilityVersion(100))
+				}
+
+				b.StopTimer()
+				// Disconnect for next iteration
+				for i := range allNodes {
+					node := &allNodes[i]
+					batcher.RemoveNode(node.n.ID, node.ch)
+				}
+				// Drain channels
+				for i := range allNodes {
+					for {
+						select {
+						case <-allNodes[i].ch:
+						default:
+							goto drained
+						}
+					}
+
+				drained:
+				}
+
+				b.StartTimer()
+			}
+		})
+	}
+}
+
+// BenchmarkFullPipeline measures the full pipeline cost: addToBatch → processBatchedChanges
+// → worker → generateMapResponse → send, with real nodes from a database.
+func BenchmarkFullPipeline(b *testing.B) {
+	if testing.Short() {
+		b.Skip("skipping full pipeline benchmark in short mode")
+	}
+
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			testData, cleanup := setupBatcherWithTestData(b, NewBatcherAndMapper, 1, nodeCount, LARGE_BUFFER_SIZE)
+			defer cleanup()
+
+			batcher := testData.Batcher
+			allNodes := testData.Nodes
+
+			// Start consumers
+			for i := range allNodes {
+				allNodes[i].start()
+			}
+
+			defer func() {
+				for i := range allNodes {
+					allNodes[i].cleanup()
+				}
+			}()
+
+			// Connect all nodes first
+			for i := range allNodes {
+				node := &allNodes[i]
+
+				err := batcher.AddNode(node.n.ID, node.ch, tailcfg.CapabilityVersion(100))
+				if err != nil {
+					b.Fatalf("failed to add node %d: %v", i, err)
+				}
+			}
+
+			// Wait for initial maps to settle
+			time.Sleep(200 * time.Millisecond) //nolint:forbidigo // benchmark coordination
+
+			b.ResetTimer()
+
+			for range b.N {
+				batcher.AddWork(change.DERPMap())
+				// Allow workers to process (the batcher tick is what normally
+				// triggers processBatchedChanges, but for benchmarks we need
+				// to give the system time to process)
+				time.Sleep(20 * time.Millisecond) //nolint:forbidigo // benchmark coordination
+			}
+		})
+	}
+}
+
+// BenchmarkMapResponseFromChange measures the cost of synchronous
+// MapResponse generation for individual nodes.
+func BenchmarkMapResponseFromChange(b *testing.B) {
+	if testing.Short() {
+		b.Skip("skipping full pipeline benchmark in short mode")
+	}
+
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	defer zerolog.SetGlobalLevel(zerolog.DebugLevel)
+
+	for _, nodeCount := range []int{10, 100} {
+		b.Run(fmt.Sprintf("%dnodes", nodeCount), func(b *testing.B) {
+			testData, cleanup := setupBatcherWithTestData(b, NewBatcherAndMapper, 1, nodeCount, LARGE_BUFFER_SIZE)
+			defer cleanup()
+
+			batcher := testData.Batcher
+			allNodes := testData.Nodes
+
+			// Start consumers
+			for i := range allNodes {
+				allNodes[i].start()
+			}
+
+			defer func() {
+				for i := range allNodes {
+					allNodes[i].cleanup()
+				}
+			}()
+
+			// Connect all nodes
+			for i := range allNodes {
+				node := &allNodes[i]
+
+				err := batcher.AddNode(node.n.ID, node.ch, tailcfg.CapabilityVersion(100))
+				if err != nil {
+					b.Fatalf("failed to add node %d: %v", i, err)
+				}
+			}
+
+			time.Sleep(200 * time.Millisecond) //nolint:forbidigo // benchmark coordination
+
+			ch := change.DERPMap()
+
+			b.ResetTimer()
+
+			for i := range b.N {
+				nodeIdx := i % len(allNodes)
+				_, _ = batcher.MapResponseFromChange(allNodes[nodeIdx].n.ID, ch)
+			}
+		})
+	}
+}