I cannot seem to be able to drive the CPU load to >85% in my Seam application stress testing. If I increase the client threads, the response time would simply increase and the CPU stays at around 85%. So, I did a thread dump, and found most HTTP threads are waiting at line 161 of class org.jboss.aop.metadata.MethodMetaData. This line is a synchronized access to a HashMap, and it is appreantly a contention point where multiple CPUs have to wait on each other.

public class MethodMetaData implements MetaDataResolver {

 public synchronized Object getMethodMetaData(Method method, Object tag, Object attr) {

 // This is line 161:
 SimpleMetaData methodData = (SimpleMetaData)methodMetaData.get(method.toString());

 }
}

Clebert suggested to use a concurrent HashMap instead of the method level synchronization here. What do you guys think?