Are your test results different when rowSize = colSize > 1000 say ??
On Sunday, September 29, 2019 at 10:18:15 AM UTC-4, zct wrote:
>
> The test code is below:
> package main
>
> import (
> "testing"
> )
>
> const rowSize = 1000000
> const colSize = 100
>
> var array [rowSize][colSize]int
>
> func BenchmarkRow(b *testing.B) {
> b.ResetTimer()
> for i := 0; i < b.N; i++ {
> sum := 0
> for r := 0; r < rowSize; r++ {
> for c := 0; c < colSize; c++ {
> sum += array[r][c]
> }
> }
> }
> }
>
> func BenchmarkColumn(b *testing.B) {
> b.ResetTimer()
> for i := 0; i < b.N; i++ {
> sum := 0
> for c := 0; c < colSize; c++ {
> for r := 0; r < rowSize; r++ {
> sum += array[r][c]
> }
> }
> }
> }
>
>
> As we known, there is a cpu cache in computer, so the row-wise should
> perform better than the column-wise. But the test result is :
>
> go test -bench=. -count=5
> goos: darwin
> goarch: amd64
> BenchmarkRow-4 30 42926367 ns/op
> BenchmarkRow-4 30 50048505 ns/op
> BenchmarkRow-4 32 38466153 ns/op
> BenchmarkRow-4 28 40887279 ns/op
> BenchmarkRow-4 30 36325967 ns/op
> BenchmarkColumn-4 34 30991838 ns/op
> BenchmarkColumn-4 36 30965998 ns/op
> BenchmarkColumn-4 39 31575142 ns/op
> BenchmarkColumn-4 33 35048352 ns/op
> BenchmarkColumn-4 38 32584167 ns/op
> PASS
>
> It show that the column-wise traverse is quicker than the row-wise. I test
> it in my macbook and ubuntu server, the result is the same
>
>
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