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Core Image performance

I have been exploring Core Image recently and have been a little surprised at the slowness of it. I am working on a 2 x 2 gig G5 with nvidia GeForce fx 5200 and a 1 gHz power book with nvidia GeForce fx 5200 go. System profiler tells me that my video cards support CoreImage.

I have been poking around with OpenGL profiler and as far as I can tell, little or nothing is being accelerated by the GPU. No programs are listed under resources and there are no calls that appear to be program related. The speed appears to be what I would expect from floating point RGB based Altivec code. My own altivec code is faster pretty much across the board.

I have tried encapsulating a very simple addition kernel in an Image Unit without interface to force it to be nonexecutable, but I am still getting the same performance. I am only making the simplest texture access so it is not because of a disallowed texture call.

I am also not seeing the kind of advantage I was expecting from the aggregation of filters into a single program. The second filter doubles the load of the first filter, where I was expecting the second filter to be much less of a drain as it should have been combined with the first, reducing various unnecessary processing steps (which also indicates to me that everything is being rendered by the CPU.

Are there other factors being factored into decisions about whether to use the GPU or CPU?
Am I missing some setting that enables GPU processing? Was I just expecting too much out of the FX5200?

Any thoughts or ideas?

David Rokeby




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