Frequent CPU spike on Openfire on Windows 2008

We are running Operfire version : 3.9.1 on Windows 2008 R2 server in a 64 bit JVM.

Very recently , we have started seeing frequent CPU spikes on the server. The threads that are taking up most of the CPU time are blocked on this offset in JVM -

jvm!JVM_FindSignal+2d7d

We are not seeing any out of memory exceptions. Also the CPU spike is generally seen during non peak hours. As a first resolution for this issue we recently increased the max heap memory from 1024mb to 2048mb but that seems to have made spikes more frequent. The server has total of 8gb memory out of which more than 4gb is free.

Please see attached screenshot for JVM version

jvm.jpg

Any idea what this offset refers to ? We are not sure what is stressing the CPU so much and if this is an indication of a problem that can get bigger.

Any help is much appreciated