Defer significantly slower

defer_bench.go

package main

import (
	"flag"
	"log"
	"runtime"
	"sync"
	"testing"
)

func deferBench(b *testing.B) {
	lock := sync.Mutex{}
	for i := 0; i < b.N; i++ {
		func() {
			lock.Lock()
			defer lock.Unlock()
		}()
	}
}

func noDeferBench(b *testing.B) {
	lock := sync.Mutex{}
	for i := 0; i < b.N; i++ {
		func() {
			lock.Lock()
			lock.Unlock()
		}()
	}
}

func main() {
	log.Println(runtime.Version())
	flag.Set("test.bench", "foo")
	flag.Set("test.v", "true")
	testing.Main(func(pat, str string) (bool, error) { return true, nil },
		[]testing.InternalTest{},
		[]testing.InternalBenchmark{{"defer benchmark", deferBench}, {"no defer bench", noDeferBench}},
		[]testing.InternalExample{})
}

results.txt

go run defer_bench.go
2015/07/13 12:02:44 devel +ca6ba49 Mon Jul 13 06:40:00 2015 +0000
testing: warning: no tests to run
PASS
defer benchmark-8	20000000	        98.8 ns/op
no defer bench-8 	100000000	        21.8 ns/op