cudaGLSetGLDevice on 2.1?

Hi, in CUDA sdk 2.1 release note, it says: (

V. Change Log

Release 2.1

  • CUDA samples that use OpenGL interop now call cudaGLSetGLDevice after the GL context is created.
    This ensures that OpenGL/CUDA interop gets the best possible performance possible.

But when I checked the sample code “simpleGL” in the sdk, I couldn’t find where udaGLSetGLDevice was used. Is this call necessary for cuda/gl interoperation?