Thank you very much for the feedback. I'm very glad to hear you like the book
You are correct in assuming that Tcpu represents the total CPU time. As you suggest, it would have been better to clearly state this.
In your second comment you bring up an interesting point. It kind of depends on the perspective and expectation. From a parallel efficiency point of view, the performance is poor, indicating many cycles are wasted if this was the only program using the processors. At the end of the day however, the elapsed time is indeed still less compared to using 2 processors. Since the cost of cores/threads is coming down, a relatively low efficiency is not so much of a concern as long as there is a reduction in elapsed time. That is at least what I notice when talking with people about efficiency versus elapsed time.
Kind regards, Ruud