This is priyank i have made one doc which can be useful for achiving better performance tunning !
JBoss AS tunning is bit of complex process which involves few things like in depth analysis of application garbage , h/w , platform and java tunning .
Hope this must be useful for your scenerio
See this earlier discussion: http://community.jboss.org/message/221052#221052
Also see the whitepaper "Scaling up the JBoss Application Server" at http://www.cmg.org/proceedings/2005.html. (I have presented quite a few Java pefromance white papers at CMG, most of them would be helpful.)
Those are all about previous versions of JBoss AS, but many of the tuning principles still apply (especially the JVM tuning).