T L,
Why didn't you show us the output from
$ go tool compile -m -m clone_test.go
?
Peter
On Tuesday, June 27, 2017 at 11:33:30 AM UTC-4, T L wrote:
>
> Ok, I think there are two reasons why the copy version is slower:
> 1. the copy version initializes each element twice actutally.
> 2. alloc a new slice by using make is slow than by using append. But why
> this?
>
> package main
>
> import (
> "testing"
> )
>
> const N = 1024 * 1024 // number of elements
> type Element int64
> var x = make([]Element, N)
> var y []Element
>
> func Benchmark_AllocWithMake(b *testing.B) {
> for i := 0; i < b.N; i++ {
> y = make([]Element, N)
> }
> }
>
> func Benchmark_AllocWithAppend(b *testing.B) {
> for i := 0; i < b.N; i++ {
> y = append([]Element(nil), x...)
> }
> }
>
> func Benchmark_CloneWithCopy(b *testing.B) {
> for i := 0; i < b.N; i++ {
> t := make([]Element, N)
> copy(t, x)
> y = t
> }
> }
>
> func Benchmark_CloneWithAppend(b *testing.B) {
> for i := 0; i < b.N; i++ {
> y = append([]Element(nil), x...)
> }
> }
>
> Benchmark_AllocWithMake-4 1000 1223666 ns/op
> Benchmark_AllocWithAppend-4 2000 725361 ns/op
> Benchmark_CloneWithCopy-4 1000 1813321 ns/op
> Benchmark_CloneWithAppend-4 2000 735011 ns/op
>
> On Tuesday, June 27, 2017 at 10:58:28 PM UTC+8, T L wrote:
>>
>>
>> package main
>>
>> import (
>> "testing"
>> )
>>
>> const N = 1024 * 1024 // number of elements
>> type Element int64
>> var x = make([]Element, N)
>> var y []Element
>>
>>
>> func Benchmark_CloneWithAppend(b *testing.B) {
>> for i := 0; i < b.N; i++ {
>> y = append([]Element(nil), x...)
>> }
>> }
>>
>> func Benchmark_CloneWithCopy(b *testing.B) {
>> b.ResetTimer()
>> for i := 0; i < b.N; i++ {
>> t := make([]Element, N)
>> copy(t, x)
>> y = t
>> }
>> }
>>
>> /*
>> $ go test -bench=.
>> Benchmark_CloneWithAppend-4 2000 738281 ns/op
>> Benchmark_CloneWithCopy-4 1000 1822462 ns/op
>> */
>>
>
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