1 files changed, 82 insertions, 0 deletions
diff --git a/src/sync/pool_test.go b/src/sync/pool_test.go
index 62085b5c96..5649a9dc83 100644
--- a/src/sync/pool_test.go
+++ b/src/sync/pool_test.go
@@ -10,6 +10,7 @@ package sync_test
 import (
 	"runtime"
 	"runtime/debug"
+	"sort"
 	. "sync"
 	"sync/atomic"
 	"testing"
@@ -253,3 +254,84 @@ func BenchmarkPoolOverflow(b *testing.B) {
 		}
 	})
 }
+
+var globalSink interface{}
+
+func BenchmarkPoolSTW(b *testing.B) {
+	// Take control of GC.
+	defer debug.SetGCPercent(debug.SetGCPercent(-1))
+
+	var mstats runtime.MemStats
+	var pauses []uint64
+
+	var p Pool
+	for i := 0; i < b.N; i++ {
+		// Put a large number of items into a pool.
+		const N = 100000
+		var item interface{} = 42
+		for i := 0; i < N; i++ {
+			p.Put(item)
+		}
+		// Do a GC.
+		runtime.GC()
+		// Record pause time.
+		runtime.ReadMemStats(&mstats)
+		pauses = append(pauses, mstats.PauseNs[(mstats.NumGC+255)%256])
+	}
+
+	// Get pause time stats.
+	sort.Slice(pauses, func(i, j int) bool { return pauses[i] < pauses[j] })
+	var total uint64
+	for _, ns := range pauses {
+		total += ns
+	}
+	// ns/op for this benchmark is average STW time.
+	b.ReportMetric(float64(total)/float64(b.N), "ns/op")
+	b.ReportMetric(float64(pauses[len(pauses)*95/100]), "p95-ns/STW")
+	b.ReportMetric(float64(pauses[len(pauses)*50/100]), "p50-ns/STW")
+}
+
+func BenchmarkPoolExpensiveNew(b *testing.B) {
+	// Populate a pool with items that are expensive to construct
+	// to stress pool cleanup and subsequent reconstruction.
+
+	// Create a ballast so the GC has a non-zero heap size and
+	// runs at reasonable times.
+	globalSink = make([]byte, 8<<20)
+	defer func() { globalSink = nil }()
+
+	// Create a pool that's "expensive" to fill.
+	var p Pool
+	var nNew uint64
+	p.New = func() interface{} {
+		atomic.AddUint64(&nNew, 1)
+		time.Sleep(time.Millisecond)
+		return 42
+	}
+	var mstats1, mstats2 runtime.MemStats
+	runtime.ReadMemStats(&mstats1)
+	b.RunParallel(func(pb *testing.PB) {
+		// Simulate 100X the number of goroutines having items
+		// checked out from the Pool simultaneously.
+		items := make([]interface{}, 100)
+		var sink []byte
+		for pb.Next() {
+			// Stress the pool.
+			for i := range items {
+				items[i] = p.Get()
+				// Simulate doing some work with this
+				// item checked out.
+				sink = make([]byte, 32<<10)
+			}
+			for i, v := range items {
+				p.Put(v)
+				items[i] = nil
+			}
+		}
+		_ = sink
+	})
+	runtime.ReadMemStats(&mstats2)
+
+	b.ReportMetric(float64(mstats2.NumGC-mstats1.NumGC)/float64(b.N), "GCs/op")
+	b.ReportMetric(float64(nNew)/float64(b.N), "New/op")
+}