diff --git a/src/pkg/runtime/malloc_test.go b/src/pkg/runtime/malloc_test.go
index 2b686a6e7e..128ec098cb 100644
--- a/src/pkg/runtime/malloc_test.go
+++ b/src/pkg/runtime/malloc_test.go
@@ -5,8 +5,10 @@
 package runtime_test
 
 import (
+	"flag"
 	. "runtime"
 	"testing"
+	"time"
 	"unsafe"
 )
 
@@ -65,3 +67,90 @@ func BenchmarkMallocTypeInfo16(b *testing.B) {
 	}
 	mallocSink = x
 }
+
+var n = flag.Int("n", 1000, "number of goroutines")
+
+func BenchmarkGoroutineSelect(b *testing.B) {
+	quit := make(chan struct{})
+	read := func(ch chan struct{}) {
+		for {
+			select {
+			case _, ok := <-ch:
+				if !ok {
+					return
+				}
+			case <-quit:
+				return
+			}
+		}
+	}
+	benchHelper(b, *n, read)
+}
+
+func BenchmarkGoroutineBlocking(b *testing.B) {
+	read := func(ch chan struct{}) {
+		for {
+			if _, ok := <-ch; !ok {
+				return
+			}
+		}
+	}
+	benchHelper(b, *n, read)
+}
+
+func BenchmarkGoroutineForRange(b *testing.B) {
+	read := func(ch chan struct{}) {
+		for _ = range ch {
+		}
+	}
+	benchHelper(b, *n, read)
+}
+
+func benchHelper(b *testing.B, n int, read func(chan struct{})) {
+	m := make([]chan struct{}, n)
+	for i := range m {
+		m[i] = make(chan struct{}, 1)
+		go read(m[i])
+	}
+	b.StopTimer()
+	b.ResetTimer()
+	GC()
+
+	for i := 0; i < b.N; i++ {
+		for _, ch := range m {
+			if ch != nil {
+				ch <- struct{}{}
+			}
+		}
+		time.Sleep(10 * time.Millisecond)
+		b.StartTimer()
+		GC()
+		b.StopTimer()
+	}
+
+	for _, ch := range m {
+		close(ch)
+	}
+	time.Sleep(10 * time.Millisecond)
+}
+
+func BenchmarkGoroutineIdle(b *testing.B) {
+	quit := make(chan struct{})
+	fn := func() {
+		<-quit
+	}
+	for i := 0; i < *n; i++ {
+		go fn()
+	}
+
+	GC()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		GC()
+	}
+
+	b.StopTimer()
+	close(quit)
+	time.Sleep(10 * time.Millisecond)
+}
diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index fe9c18177c..7ebc2912ea 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -19,7 +19,7 @@ enum {
 	Debug = 0,
 	DebugMark = 0,  // run second pass to check mark
 	CollectStats = 0,
-	ScanStackByFrames = 1,
+	ScanStackByFrames = 0,
 	IgnorePreciseGC = 0,
 
 	// Four bits per word (see #defines below).
@@ -1474,6 +1474,7 @@ addstackroots(G *gp)
 		USED(guard);
 		runtime·gentraceback(pc, sp, lr, gp, 0, nil, 0x7fffffff, addframeroots, nil, false);
 	} else {
+		USED(lr);
 		USED(pc);
 		n = 0;
 		while(stk) {