ptr vs value benchmark

gistfile1.txt

package main

import (
    "testing"
    "strconv"
)

type Data struct {
    Name string
    Tags []string
}

type MapWithPtrs struct {
    Items map[int]*Data
}

type MapWithoutPtrs struct {
    Items map[int]Data
}

var (
    mwp *MapWithPtrs
    mwop *MapWithoutPtrs
)

func init() {
    mwp = &MapWithPtrs{
        Items: make(map[int]*Data),
    }
    for i:=0; i < 5000000; i++ {
        mwp.Items[i] = &Data{
            Name: "data"+strconv.Itoa(i),
            Tags: []string{"foo", "baz", "bar", "one", "two", "three", "tag"+strconv.Itoa(i)},
        }
    }
    mwop = &MapWithoutPtrs{
        Items: make(map[int]Data),
    }
    for i:=0; i < 5000000; i++ {
        mwop.Items[i] = Data{
            Name: "data"+strconv.Itoa(i),
            Tags: []string{"foo", "baz", "bar", "one", "two", "three", "tag"+strconv.Itoa(i)},
        }
    }
}


func BenchmarkPtr(b *testing.B) {
    for n:=0; n <b.N; n++ {
        if data, ok := mwp.Items[n]; ok {
            data.Tags = append(data.Tags, "blah")
        }
    }
}

func BenchmarkNoPtr(b *testing.B) {
    for n:=0; n <b.N; n++ {
        if data, ok := mwop.Items[n]; ok {
            data.Tags = append(data.Tags, "blah")
            mwop.Items[n] = data
        }
    }
} 

same outcome when I change BenchmarkListPtr to use

    for i := 1; i <= times; i++ {
        for n := 0; n < b.N; n++ {
            lwp[n].Tags = append(lwp[n].Tags, "blah")
        }
    }