util/eventbus: add basic throughput benchmarks (#15284)

Shovel small events through the pipeine as fast as possible in a few basic
configurations, to establish some baseline performance numbers.

Updates #15160

Change-Id: I1dcbbd1109abb7b93aa4dcb70da57f183eb0e60e
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>

util/eventbus/bench_test.go

@@ -0,0 +1,125 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package eventbus_test
+
+import (
+	"math/rand/v2"
+	"testing"
+
+	"tailscale.com/util/eventbus"
+)
+
+func BenchmarkBasicThroughput(b *testing.B) {
+	bus := eventbus.New()
+	pcli := bus.Client(b.Name() + "-pub")
+	scli := bus.Client(b.Name() + "-sub")
+
+	type emptyEvent [0]byte
+
+	// One publisher and a corresponding subscriber shoveling events as fast as
+	// they can through the plumbing.
+	pub := eventbus.Publish[emptyEvent](pcli)
+	sub := eventbus.Subscribe[emptyEvent](scli)
+
+	go func() {
+		for {
+			select {
+			case <-sub.Events():
+				continue
+			case <-sub.Done():
+				return
+			}
+		}
+	}()
+
+	for b.Loop() {
+		pub.Publish(emptyEvent{})
+	}
+	bus.Close()
+}
+
+func BenchmarkSubsThroughput(b *testing.B) {
+	bus := eventbus.New()
+	pcli := bus.Client(b.Name() + "-pub")
+	scli1 := bus.Client(b.Name() + "-sub1")
+	scli2 := bus.Client(b.Name() + "-sub2")
+
+	type emptyEvent [0]byte
+
+	// One publisher and two subscribers shoveling events as fast as they can
+	// through the plumbing.
+	pub := eventbus.Publish[emptyEvent](pcli)
+	sub1 := eventbus.Subscribe[emptyEvent](scli1)
+	sub2 := eventbus.Subscribe[emptyEvent](scli2)
+
+	for _, sub := range []*eventbus.Subscriber[emptyEvent]{sub1, sub2} {
+		go func() {
+			for {
+				select {
+				case <-sub.Events():
+					continue
+				case <-sub.Done():
+					return
+				}
+			}
+		}()
+	}
+
+	for b.Loop() {
+		pub.Publish(emptyEvent{})
+	}
+	bus.Close()
+}
+
+func BenchmarkMultiThroughput(b *testing.B) {
+	bus := eventbus.New()
+	cli := bus.Client(b.Name())
+
+	type eventA struct{}
+	type eventB struct{}
+
+	// Two disjoint event streams routed through the global order.
+	apub := eventbus.Publish[eventA](cli)
+	asub := eventbus.Subscribe[eventA](cli)
+	bpub := eventbus.Publish[eventB](cli)
+	bsub := eventbus.Subscribe[eventB](cli)
+
+	go func() {
+		for {
+			select {
+			case <-asub.Events():
+				continue
+			case <-asub.Done():
+				return
+			}
+		}
+	}()
+	go func() {
+		for {
+			select {
+			case <-bsub.Events():
+				continue
+			case <-bsub.Done():
+				return
+			}
+		}
+	}()
+
+	var rng uint64
+	var bits int
+	for b.Loop() {
+		if bits == 0 {
+			rng = rand.Uint64()
+			bits = 64
+		}
+		if rng&1 == 0 {
+			apub.Publish(eventA{})
+		} else {
+			bpub.Publish(eventB{})
+		}
+		rng >>= 1
+		bits--
+	}
+	bus.Close()
+}