hotspot profiler experience and accuracy?

[aurora]

I have a parser I need to optimize. It has some disk IO and a lot of  
looping over characters.

I used the hotspot profiler to gain insight on optimization options. The  
methods show up on on the top of this list seems fairly trivial and does  
not look like CPU hogger. Nevertheless I optimized it and have 25%  
performance gain according to hotspot's number.

But the numbers look skeptical. Hotspot claim 71.166 CPU seconds but the  
actual elapsed time is only 54s. When measuring elapsed time instead of  
CPU time the performance gain is only 13% with the profiler running and  
down to 10% when not using the profiler.

Is there something I misunderstood in reading the numbers?