The application is heavily dependent in UDP API. Its a SIP application server. ISV is seeing an ~50% degradation in performance on jdk1.4....an extra 50% time being spent as System time, compared to JDK1.3
Initial investigation shows that there is a huge Spin count no. on udp_g_lock in jdk1.4, which is not there when the application is run on jdk1.3
Seems like the UDP implementation has changed from jdk1.3 to jdk1.4, resulting in this effect.