How to get real time of parallel code

[jzakiya]

When I run this:
    
    
    let t1 = cpuTime()
    
    # some single threaded code
    
    echo("time = ", cpuTime()-t1
    

I get the correct time (in secs), but when the code is executing in parallel 
the result is greater than real (clock) time.

What do you use to return the true clock time (stop watch) difference?