benchmarking question (from newbie)

[Jacq]

Hello,

I am a student of "language and artificial intelligence".
I would be very grateful if anyone could advise me on a
benchmarking question I have:

What I have is a script that repeatedly calls a machine-learning
program each time with different parameters/algorithms.
What I need is to measure the time the machine-learning-programme
takes running, *independent* of other processes running on the
same machine.
(I have no control over what processes are started up
by other users, and I want to compare the speed of the different
algorithms/parameter-combinations.)

I thought I could use something like this:
    start = time.clock()
    os.system("call to machine-learning program")
    stop = time.clock()
    cpuTime = stop - start
But testing this on my own machine, I get different values for the same
program-call depending on what other processes I have started on my
machine.

I use Python 1.5 on linux (RedHat 6.1)

Thanks,

Jacqueline Dake