go performance for multi core machines

coreperf.go

package main

import (
	"flag"
	"fmt"
	"math/rand"
	"runtime"
	"sync"
	"sync/atomic"
	"time"
)

func main() {
	var threads int
	var N int
	flag.IntVar(&threads, "t", 0, "number of threads, 0 = host cpus")
	flag.IntVar(&N, "n", 10000000000, "number of ops per thread")
	flag.Parse()
	if threads <= 0 {
		threads = runtime.NumCPU()
	}
	var f int64
	var wg sync.WaitGroup
	wg.Add(threads)
	rand.Seed(time.Now().UnixNano())
	start := time.Now()
	for i := 0; i < threads; i++ {
		go func(r, n int) {
			var t int
			for j := 0; j < n; j++ {
				t += r * j
			}
			atomic.AddInt64(&f, int64(t))
			wg.Done()
		}(rand.Int(), N)
	}
	wg.Wait()
	dur := time.Since(start)
	fmt.Printf("%s ops over %s threads in %s (%s ops/sec)\n",
		commaize(N*threads), commaize(threads), dur, commaize(int(float64(N*threads)/dur.Seconds())))
}

func commaize(n int) string {
	nstr1, nstr := fmt.Sprintf("%d", n), ""
	for i, j := len(nstr1)-1, 0; i >= 0; i, j = i-1, j+1 {
		nstr = string(nstr1[i]) + nstr
		if i != 0 && j%3 == 2 {
			nstr = "," + nstr
		}
	}
	return nstr
}