CPU Cache Line vs Memory Speed

main.go

package main

import (
	"fmt"
	"time"
)

type BigStruct struct {
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
	_ int64
}

func main() {
	a := make([][]BigStruct, 1e4)
	for i := range a {
		a[i] = make([]BigStruct, 1e4)
	}

	s := time.Now()
	var m BigStruct
	for i := 0; i < len(a); i++ {
		for j := len(a[i]); j < len(a[i]); j++ {
			m = a[i][j]
		}
	}

	fmt.Println(time.Since(s))

	s = time.Now()
	for i := 0; i < len(a); i++ {
		for j := len(a[i]); j < len(a[i]); j++ {
			m = a[j][i]
		}
	}

	fmt.Println(time.Since(s))

	// just to fool compiler
	func(m BigStruct) {}(m)
}