go - Goroutines don't work in parallel -

given following code:

package main  import (     "fmt"     "runtime"     "time" )   func f(from string) {      := 0; < 3; i++ {         fmt.println(from, ":", i)         //runtime.gosched()     } }  func main() {      runtime.gomaxprocs(runtime.numcpu()*2)     time.sleep(100)      go f("i not parallel")      go f("neither me")      var input string     fmt.scanln(&input) } 

the output in cases is:

i not parallel : 0
not parallel : 1
not parallel : 2
neither me : 0
neither me : 1
neither me : 2

and sometimes:

neither me : 0
neither me : 1
neither me : 2
not parallel : 0
not parallel : 1
not parallel : 2

when runtime.gosched() uncommented seems ok. have tried changing gomaxprocs number 2 numcpu, number of goroutines, cycles: none work in parallel.
why strange behaviour?

edit: ok, seems context-switching heavy work , not done without reasonable matters. 1 thing still can't understand - why people get work without sleep instructions?

you should not predict goroutine schedule. running example provided, got output.

direct : 0 direct : 1 direct : 2 goroutine : 0 goroutine : 1 goroutine : 2 going done 

if add runtime.gomaxprocs(4) @ begin of main function, , run on i5 qcore desktop ubuntu, output

direct : 0 direct : 1 direct : 2 goroutine : 0 goroutine : 1 goroutine : 2 going  done 

it not produce same output think. should assume goroutine may parallel, add lock if need control sequence.