From my point of view, you just turn on the profiler and start your application.
I would first only start and stop the application, then you know where the general code is spending most of the time.
Next I would test one feature after the other separately, so start the application use a feature and stop the application to check the profiler.
It is easier to test step by step instead of a bunch of features and then being not able to distinguish between the single features.
Just my two cents, since I haven't used the profiler of Pelles C, but of other IDE's for other languages.