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c++copencl
Henry Gomersall
Henry Gomersall

Reputation: 8692

Advantages of a program containing several OpenCL kernels versus several programs with one kernel each?

This question derives from my desire to have an OpenCL program constructed at runtime from various kernels. So, imagine I have various kernels that I want to execute in a given context with the same set of memory objects.

If I knew ahead of time all the kernels I wanted to combine into a program, I'd have no problem - simply create a program with all the kernel sources or binaries.

However, given that I don't know ahead of time which kernels I want to combine I was considering creating one program for each kernel source. Is this equivalent to the original case (assuming the compile time options are all the same)? Is there a performance penalty in calling kernels that reside in different programs?

The problem is possibly that I don't understand the abstraction of a "program". What is it? Is it more than just a collection of kernels and some compile time options?

Upvotes: 3

Views: 909

Answers (1)

Kyle Lutz
Kyle Lutz

Reputation: 8036

There are a couple of benefits of grouping OpenCL kernels into a single program:

  1. The (slight) overhead of invoking the compiler multiple times through multiple clBuildProgram() calls. This can be avoided by compiling a single source string into a single program and then creating multiple kernels from it. However, after you get a kernel object there should be no difference in performance based on the program it came from.

  2. The more significant benefit: Grouping kernels together in programs allows them to reference and use each-other and/or other associated helper functions.

    Example: A program might define a function to convert between spherical and Cartesian coordinates which could then be used by multiple kernels without its source needing to be duplicated.

Upvotes: 4

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