Performance degradation when migrating from JRockit to Oracle JDK 7

Same WebLogic 10.3.6
Before: JRockit R28 (6)
After: latest Oracle Java 7 (1.7.0_96) (also happened with 1.7.0._75)

Although the throughput in terms of GC times is better, the CPU usage is
higher, but Not worrying initially. But after the CPU usage is increasing
continuously and finally customer has to go back to JRockit again.

In the recordings, we see that the hot methods that are increasing after time
are related with internal serialization:

java.io.ObjectStreamClass
java.io.ObjectOutputStream
java.io.ObjectInputStream

These methods pressure have been increased a lot since the beginning and they
seem to be the responsible of the CPU usage increase.
GC is managing the memory OK, I think that the problem is not related with
memory management.