Benchmarking invoking defer fn() vs fn()

deferbench_test.go

package main

import (
	"sync"
	"testing"
)

type st struct {
	sync.Mutex

	i int
}

func (c *st) callDefer() error {
	c.Lock()
	defer c.Unlock()

	c.i += 1
	return nil
}

func (c *st) callNoDefer() error {
	c.Lock()
	c.i += 1
	c.Unlock()

	return nil
}

func BenchmarkNoDefer(b *testing.B) {
	var err error
	it := new(st)
	for i := 0; i < b.N; i++ {
		err = it.callNoDefer()
	}
	b.ReportAllocs()
	if err != nil {
	}
}

func BenchmarkDefer(b *testing.B) {
	var err error
	it := new(st)
	for i := 0; i < b.N; i++ {
		err = it.callDefer()
	}
	b.ReportAllocs()
	if err != nil {
	}
}

inspection.md

$ benchstat before.txt after.txt 
name     old time/op    new time/op    delta
Defer-4    23.1ns ± 3%    51.2ns ± 1%  +121.22%        (p=0.000 n=10+10)

name     old alloc/op   new alloc/op   delta
Defer-4    0.00B ±NaN%    0.00B ±NaN%      ~     (all samples are equal)

name     old allocs/op  new allocs/op  delta
Defer-4     0.00 ±NaN%     0.00 ±NaN%      ~     (all samples are equal)

where:

• before.txt -- without defer
• after.txt -- with defer

stats.md

$ go version && go test -v -run=^$ -bench=. -count=10
go version devel +f612cd7 Thu Aug 10 01:35:28 2017 +0000 darwin/amd64
goos: darwin
goarch: amd64
BenchmarkNoDefer-4   	100000000	        23.3 ns/op	       0 B/op	       0 allocs/op
BenchmarkNoDefer-4   	100000000	        23.3 ns/op	       0 B/op	       0 allocs/op
BenchmarkNoDefer-4   	100000000	        23.3 ns/op	       0 B/op	       0 allocs/op
BenchmarkNoDefer-4   	100000000	        23.9 ns/op	       0 B/op	       0 allocs/op
BenchmarkNoDefer-4   	100000000	        23.0 ns/op	       0 B/op	       0 allocs/op
BenchmarkNoDefer-4   	100000000	        22.8 ns/op	       0 B/op	       0 allocs/op
BenchmarkNoDefer-4   	100000000	        22.8 ns/op	       0 B/op	       0 allocs/op
BenchmarkNoDefer-4   	100000000	        23.4 ns/op	       0 B/op	       0 allocs/op
BenchmarkNoDefer-4   	100000000	        22.9 ns/op	       0 B/op	       0 allocs/op
BenchmarkNoDefer-4   	100000000	        22.7 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        51.5 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        51.0 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        51.1 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        51.4 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        51.5 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        50.9 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        51.2 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        50.8 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        50.6 ns/op	       0 B/op	       0 allocs/op
BenchmarkDefer-4     	30000000	        51.9 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	_/Users/emmanuelodeke/Desktop/benchmarking/defers	39.249s