How To Structure Large OpenCL Kernels?

Question

I have worked with OpenCL on a couple of projects, but have always written the kernel as one (sometimes rather large) function. Now I am working on a more complex project and would like to share functions across several kernels.

But the examples I can find all show the kernel as a single file (very few even call secondary functions). It seems like it should be possible to use multiple files - clCreateProgramWithSource() accepts multiple strings (and combines them, I assume) - although pyopencl's Program() takes only a single source.

So I would like to hear from anyone with experience doing this:

• Are there any problems associated with multiple source files?
• Is the best workaround for pyopencl to simply concatenate files?
• Is there any way to compile a library of functions (instead of passing in the library source with each kernel, even if not all are used)?
• If it's necessary to pass in the library source every time, are unused functions discarded (no overhead)?
• Any other best practices/suggestions?

Thanks.

Answer 1

I don't think OpenCL has a concept of multiple source files in a program - a program is one compilation unit. You can, however, use #include and pull in headers or other .cl files at compile time.

You can have multiple kernels in an OpenCL program - so, after one compilation, you can invoke any of the set of kernels compiled.

Any code not used - functions, or anything statically known to be unreachable - can be assumed to be eliminated during compilation, at some minor cost to compile time.