However, I have experienced significant differences with the CPU clock timers and the time of day clock timers when running interactively at least with Fortran programs. If possible, try to run under Loadleveler with the high-speed switch to avoid conflicts with other jobs and traffic regardless of the timer. One should achieve more accurate and consistent results by submitting jobs to Loadleveler. Considerations One must be cautious when timing a programming segment. Below I list factors which may bias one's timing and lead to erroneous times.
Significant times Be wary of timing a programming segment that requires little time to run.
Although one can simply enclose the programming segment in a loop, be cautious. See Code elimination and Artificially high cache performance. In the interest of accurate timing, programmers will often attempt to increase the time required to run a programming segment by putting the segment in a loop. The resulting time can be divided by the number of times the segment was executed to obtain a good average time cost. The danger with this approach is that preprocessors can deduce that no useful work is done by the computations, and may eliminate the programming segments from being executed.