Profile your application to find the most compute intensive parts. These are the parts that might be worth porting to OpenCL.
The proportion of an application that requires high performance is often a
relatively small part of the code. This is the part of the code that can make best use of
OpenCL. Porting any more of the application to OpenCL is unlikely to provide a benefit.
You can use profilers such as DS-5 to profile your application.