By default, Prefix only instruments key, pre-defined events in the IIS pipeline and page lifecycle. One of the key benefits of the profiler, however, is that you may instrument how long any .NET method takes to execute and include that output in the call stack.
In deciding what to profile, keep in mind the overhead that could be incurred. For example, if you choose to use a wildcard configuration as described below, all .NET properties that have Get and Set accessors (which includes dynamic properties) will be profiled via these accessors, and can be quite “chatty.”
Custom Config Editor
In order to get around the "Unknown Application Code" message in Prefix, you'll need to add some custom configuration to tell Prefix to profile certain classes and methods that are not profiled by default. With Prefix Premium, you can use the Custom Config Editor to define which classes and methods to be profiled in your code.
All you will need to do is select your app, the assemblies, classes, and methods all within the editor and then save your selections.
Once completed, you will now see your custom code in the trace details.