why does java not use 100% CPU

[gid15]

heres the log you asked I am trying to play the 3rd birthday and my max FPS is 25-30 and it dips to 17-20 I am in the first mission after the tutorial
and my cpu usage of java is ranging in from 40-58% max and I noticed that when it dips frames the cpu use drops to 40% and goes back up to 50% and above after that it runs a few fine frames and then dips again as I said in the first post changing Java.exe priority from normal, above normal, and High changes nothing but when I used realtime CPU usage boost from a mere 40-55% to 50-68% and then the dips disappears and I get a playable game I could play it now but I am still very much wonderin about why its doin that

PS:
sorry bout that forgot to answer your question when running the skinning app I got around 38-49% cpu and its not dipping frames LOL

Hmmm... your log file is almost empty, this is not normal. Are you sure you have set the log level to INFO before loading the game? and that you are using a fresh installation from http://buildbot.orphis.net/jpcsp/ (i.e. an installation where you have not tweaked the log settings using Debug -> Tools -> Logger -> Customize...).

BTW, from the video posted on the game thread, a FPS around 20 seems to be normal. So I don't think there is something wrong...