Measure it.
I always set up a spare 16 or 32 bit hardware timer running at 1MHz. On the MCF5329 I'm using, that's one of the DMA Timers. Then any code can read "the current time in microseconds" either side of a function, event or task. It can print it, store it in a variable (for inspection in the debugger), accumulate, log or whatever you want to do.
Of course the simplest thing is to turn a LED on that is connected to a hardware pin at point "A" in your code and turn it off at point "B". You then measure the time with an oscilloscope. Make sure to measure the overhead of turning the LED on and off, as on some hardware ports it can be surprisingly slow. I've worked on a non-Freescale CPU that took 200 or more CPU clocks to write to a GPIO pin!
Tom