You'll likely get some alternate opinions on this, especially from the SysAdmin types amongst us, but that the algorithm used makes full use of your cpu should be seen as a good thing not a bad. Assuming the algorithm is optimal, if the code didn't utilise 100% of your cpu, then it would indicate the there was a bottleneck somewhere and it would therefore take longer, in elapsed time to complete.

That's a gross simplification of a complex issue, but to my way of thinking, there is little point in having a powerful processor, and then not utilising it to its fullest when the opportunity allows this. Of course, if the processor is shared, and the utilisation of one process is to the detriment of another, more or equally urgent task, it could be seen as a 'problem', but that is what priorities are for.

If you need or desire to lower usage of that one task, to favour others, you might look at using Win32::Process and the SetPriorityClass() call to acheive it. You should? be able to use Win32::Process::open() to obtain a OS native handle to the current task from its pid, and adjust the priority from with the same script, although I haven't actually tried this.