There are many dimensions to the performance of a computer system, and many resources consumed. The first resource to measure is wall-clock time, the total time that passes for the computation. Logging wall-clock time is particularly valuable because it can inform about unpredictable circumstances that arise in situations where other profiling is impractical. However, this may not always represent the whole picture. Sometimes something that takes a little longer but doesn't burn up so many processor seconds will be much better in the computing environment you actually have to deal with. Similarly, memory, network bandwidth, database or other server accesses may, in the end, be far more expensive than processor seconds.