On Sunday, April 23, 2017 at 12:20:52 AM UTC+8, Jan Mercl wrote:
>
> You need to define what do _you_ consider 'reliable' to get a useful
> answer.
>
calculate the sum of a number array elements.
>
> On Sat, Apr 22, 2017, 17:26 T L <tapi...@gmail.com <javascript:>> wrote:
>
>> I write a benchmark, but the results of the following 3 cases are much
>> different.
>> Which one is reliable?
>>
>> package main
>>
>> import (
>> "testing"
>> "runtime"
>> )
>>
>> const N = 200 * 1000
>> type Element int64
>> var sum int
>>
>> func Benchmark_MaybeOptimizedOut(b *testing.B) {
>> var a [N]Element
>> b.ResetTimer()
>> var g int
>> for i := 0; i < b.N; i++ {
>> for j := 0; j < len(a); j++ {
>> g += int(a[j])
>> }
>> }
>> }
>>
>> func Benchmark_AssignToGlobal(b *testing.B) {
>> var a [N]Element
>> b.ResetTimer()
>> var g int
>> for i := 0; i < b.N; i++ {
>> for j := 0; j < len(a); j++ {
>> g += int(a[j])
>> }
>> }
>> sum = g
>> }
>>
>> func Benchmark_KeepAlive(b *testing.B) {
>> var a [N]Element
>> b.ResetTimer()
>> var g int
>> for i := 0; i < b.N; i++ {
>> for j := 0; j < len(a); j++ {
>> g += int(a[j])
>> }
>> }
>> runtime.KeepAlive(&g)
>> }
>>
>> /* output:
>> $ go test -bench=. -benchtime=3s
>> Benchmark_MaybeOptimizedOut-4 50000 87318 ns/op
>> Benchmark_AssignToGlobal-4 20000 205934 ns/op
>> Benchmark_KeepAlive-4 10000 620351 ns/op
>> */
>>
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> --
>
> -j
>
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