how to benchmark the speed of an app

what is the best way to benchmark the speed of apps, say time how fast an app runs to completion? Is there a universal way to time an app runs to completion for both interpreted and compiled languages?

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I dont want to know which programming language is fastest, I want to be able to time the speed of an app compiled with different optiimizations in a compiler, or time the speed of an app compiled in different brands of compiler, stuff like that