golang defer has an associated performance cost

golang defer keyword doesn't come free. Let's see this in action 

main_test.go 

package main

import (

  "sync"

  "testing"

)

func withoutDefer() {

    mu.Lock()

    // critical section

    mu.Unlock()

}

func withDefer() {

    mu.Lock()

    defer mu.Unlock()

    // critical section

}

var mu sync.Mutex

func BenchmarkWithoutDefer(b *testing.B) {

    for i := 0; i < b.N; i++ {

        withoutDefer()

    }

}

func BenchmarkWithDefer(b *testing.B) {

    for i := 0; i < b.N; i++ {

        withDefer()

    }

} 

Run the following command 

go test -bench=.

Performance results shows that it can be slower as shown here