Well, it depends on how you've made it. For something like that, I'd go with a NURBS cylinder and make some smaller cylinders going through the main one where the holes should be, and cut them using Intersect Surfaces (or fillet if you need a rounded edge) and trim the surfaces.

Smoothing polys or sub-d's is too complicated with stuff like this imo, because you have to have as many quads as possible...