concurrency in go -Taking same time with different no of CPU - go

Question

I am running a go concurrent program with the below two case and observed that It is taking same time irrespective of no of CPU it using while execution.
Case1: When cpuUsed = 1
program took 3m20.973185s.
when I am increasing the no of CPU used.
Case2: when cpuUsed = 8
program took 3m20.9330516s.
Please find the below Go code for more details.
package main
import (
"fmt"
"math/rand"
"runtime"
"sync"
"time"
)
var waitG sync.WaitGroup
var cpuUsed = 1
var maxRandomNums = 1000
func init() {
maxCPU := runtime.NumCPU() //It'll give us the max CPU :)
cpuUsed = 8 //getting same time taken for 1 and 8
runtime.GOMAXPROCS(cpuUsed)
fmt.Printf("Number of CPUs (Total=%d - Used=%d) \n", maxCPU, cpuUsed)
}
func main() {
start := time.Now()
ids := []string{"rotine1", "routine2", "routine3", "routine4"}
waitG.Add(4)
for i := range ids {
go numbers(ids[i])
}
waitG.Wait()
elapsed := time.Since(start)
fmt.Printf("\nprogram took %s. \n", elapsed)
}
func numbers(id string) {
rand.Seed(time.Now().UnixNano())
for i := 1; i <= maxRandomNums; i++ {
time.Sleep(200 * time.Millisecond)
fmt.Printf("%s-%d ", id, rand.Intn(20)+20)
}
waitG.Done()
}

Answer 1

you will find out:
total time (3 min 20s) = 200s = sleep(200ms) * loops(1000)
Let's simplify your code and focus on CPU usage:
Remove the Sleep, which does not use the CPU at all
fmt.Println as a stdio, does not use the CPU
Random number did nothing but introduce uncertainty into the program, remove it
The only code that takes CPU in the goroutine is the "rand.Intn(20)+20", making it a constant addition
Increase the "maxRandomNums"
then your code will be like this, run it again
package main
import (
"fmt"
"runtime"
"sync"
"time"
)
var waitG sync.WaitGroup
var cpuUsed = 1
var maxRandomNums = 1000000000
func init() {
maxCPU := runtime.NumCPU() //It'll give us the max CPU :)
cpuUsed = 8 //getting same time taken for 1 and 8
runtime.GOMAXPROCS(cpuUsed)
fmt.Printf("Number of CPUs (Total=%d - Used=%d) \n", maxCPU, cpuUsed)
}
func main() {
start := time.Now()
ids := []string{"rotine1", "routine2", "routine3", "routine4"}
waitG.Add(4)
for i := range ids {
go numbers(ids[i])
}
waitG.Wait()
elapsed := time.Since(start)
fmt.Printf("\nprogram took %s. \n", elapsed)
}
func numbers(id string) {
// rand.Seed(time.Now().UnixNano())
for i := 1; i <= maxRandomNums; i++ {
// time.Sleep(200 * time.Millisecond)
// fmt.Printf("%s-%d ", id, rand.Intn(20)+20)
_ = i + 20
}
waitG.Done()
}