Fusion 9's OpenCL "Acceleration"

I promised in my initial review of Fusion 9 to do some speed tests. Blackmagic claims that every tool has been rewritten to offer GPU acceleration with OpenCL. Naturally, that's of great interest to pretty much everyone, especially those of us with access to overpowered Titan X cards. Alas, the news is not so good.

Although I can say for certain that almost every tool does, indeed, now run in OpenCL mode, the results of my testing indicate that most of them are now slower. There are a couple of exceptions, and in those cases the improvement is dramatic, but by and large, your comps will probably run faster with OpenCL disabled, regardless of your hardware.

I began my tests with the tools in the Blur category, comparing Fusion 8 and Fusion 9. Generally, Fusion 8 rendered around 30% faster. The notable exceptions were the Directional Blur and Vector Motion Blur nodes, which were up to 10x faster in Fusion 9. Since those have always been among Fusion's slowest tools, the speed-up there is most welcome. If it means everything else is 30% slower, though, the savings are quickly squandered.

Some test comps from Teen Wolf and NCIS showed similar results—in general, Fusion 8 was faster. To eliminate the possibility that there was some other factor in play, I decided to start testing Fusion 9 against itself with varying OCL settings as I moved into the Color tools.

OCL caching is turned off by default. One of the slowest parts of an OCL process is moving images in and out of the GPU's memory. By setting Caching to Full, the image should remain in GPU memory until all of the needed OCL calculations are finished, and only the final image should be moved back into system RAM. Testing showed that Full Caching did indeed speed up the tools significantly; they were up to twice as fast with it on, and as much as 50% faster with it set to Basic. However, the CPU mode still smoked OCL.

In order to sanity check myself, I shared my findings with the beta testers, and at least one reported similar results (if anyone else ran tests, they did not publish the findings).

Hopefully BMD will do some benchmarking of their own to either confirm or dispute my tests, and if it's found that I'm right, they can tune things for better performance. In the meantime, it might be worth setting defaults on most tools to turn OpenCL off (the switch is in the Common Controls tab).

Fusion 9 still needs its shakedown cruise—there are still some unfortunate bugs, and it tends to be a little bit unstable. I am pretty happy with most of the new features, though. I've been using the Delta Keyer in production for the past couple of weeks, and it does a marvelous job. So by no means am I saying don't use Fusion 9. Just don't use it because you're expecting it to be faster than 8.

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