runtime: move pinner variable into inner loop for benchmarks

Currently the pinner is created outside of the benchmarking loop.
However, this means that we get to reuse the same pinner for each loop;
in general, users are expected to create a pinner for a e.g. a cgo
call and then that variable will expire with the frame it lives in. (If
they can reuse the variable, great! However, I don't expect that to be
common.)

In essence, this benchmarks a harder case. It's not more right or wrong
than the previous version, but the fact that it's a slightly harder case
(that still mostly captures what the original version was capturing) is
useful.

Change-Id: I94987127f54d7bfecd7b8e6a5e632631ea57ad24
Reviewed-on: https://go-review.googlesource.com/c/go/+/497616
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>

src/runtime/pinner_test.go

@@ -376,9 +376,9 @@ func BenchmarkPinnerPinUnpinBatch(b *testing.B) {
 	for i := 0; i < Batch; i++ {
 		data[i] = new(obj)
 	}
-	var pinner runtime.Pinner
 	b.ResetTimer()
 	for n := 0; n < b.N; n++ {
+		var pinner runtime.Pinner
 		for i := 0; i < Batch; i++ {
 			pinner.Pin(data[i])
 		}
@@ -392,9 +392,9 @@ func BenchmarkPinnerPinUnpinBatchDouble(b *testing.B) {
 	for i := 0; i < Batch; i++ {
 		data[i] = new(obj)
 	}
-	var pinner runtime.Pinner
 	b.ResetTimer()
 	for n := 0; n < b.N; n++ {
+		var pinner runtime.Pinner
 		for i := 0; i < Batch; i++ {
 			pinner.Pin(data[i])
 			pinner.Pin(data[i])
@@ -409,9 +409,9 @@ func BenchmarkPinnerPinUnpinBatchTiny(b *testing.B) {
 	for i := 0; i < Batch; i++ {
 		data[i] = new(bool)
 	}
-	var pinner runtime.Pinner
 	b.ResetTimer()
 	for n := 0; n < b.N; n++ {
+		var pinner runtime.Pinner
 		for i := 0; i < Batch; i++ {
 			pinner.Pin(data[i])
 		}
@@ -420,27 +420,24 @@ func BenchmarkPinnerPinUnpinBatchTiny(b *testing.B) {
 }
 
 func BenchmarkPinnerPinUnpin(b *testing.B) {
-	var pinner runtime.Pinner
-	b.ResetTimer()
 	for n := 0; n < b.N; n++ {
+		var pinner runtime.Pinner
 		pinner.Pin(new(obj))
 		pinner.Unpin()
 	}
 }
 
 func BenchmarkPinnerPinUnpinTiny(b *testing.B) {
-	var pinner runtime.Pinner
-	b.ResetTimer()
 	for n := 0; n < b.N; n++ {
+		var pinner runtime.Pinner
 		pinner.Pin(new(bool))
 		pinner.Unpin()
 	}
 }
 
 func BenchmarkPinnerPinUnpinDouble(b *testing.B) {
-	var pinner runtime.Pinner
-	b.ResetTimer()
 	for n := 0; n < b.N; n++ {
+		var pinner runtime.Pinner
 		p := new(obj)
 		pinner.Pin(p)
 		pinner.Pin(p)
@@ -449,32 +446,29 @@ func BenchmarkPinnerPinUnpinDouble(b *testing.B) {
 }
 
 func BenchmarkPinnerPinUnpinParallel(b *testing.B) {
-	b.ResetTimer()
 	b.RunParallel(func(pb *testing.PB) {
-		var pinner runtime.Pinner
 		for pb.Next() {
+			var pinner runtime.Pinner
 			pinner.Pin(new(obj))
 			pinner.Unpin()
 		}
 	})
 }
 
 func BenchmarkPinnerPinUnpinParallelTiny(b *testing.B) {
-	b.ResetTimer()
 	b.RunParallel(func(pb *testing.PB) {
-		var pinner runtime.Pinner
 		for pb.Next() {
+			var pinner runtime.Pinner
 			pinner.Pin(new(bool))
 			pinner.Unpin()
 		}
 	})
 }
 
 func BenchmarkPinnerPinUnpinParallelDouble(b *testing.B) {
-	b.ResetTimer()
 	b.RunParallel(func(pb *testing.PB) {
-		var pinner runtime.Pinner
 		for pb.Next() {
+			var pinner runtime.Pinner
 			p := new(obj)
 			pinner.Pin(p)
 			pinner.Pin(p)