Rake performance on different platforms

Hi,
I have question that is related to rake cpu usage.

I am running a rake task that parses a huge xml file and inserts data
into mysql db using activerecord. On my macbook pro (2GB memory,2.2 Ghz,
leopard) the rake tasks takes about 80% CPU while running and gets the
job done in about 400 secs.

I tried the same rake task on a Ubuntu Server ( version 7.04, 8GB mem,
Xeon Quad Core) and got the job done is 1000 secs. CPU usage was about
10% for the rake task. There were no other processes that were taking
any significant CPU cycles.

On Fedora 8, 8GB mem, Xeon Quad Core the task took 529 secs. CPU usage
was about 27% for the rake task. There were no other processes that were
taking any significant CPU cycles.

what could be the problem that is forcing rake process only 10-25% of
the CPU cycles on linux distros.

thanks,

sjoshi