Sounds like its got a similar problem to aao, where most of the time its faster, by a long way, but in certain circumstances its actually slower.
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Looks like another little promising bit of code in development though, almost as if the new code skipps using octree alltogether, but then again, i know little about coding.
… Sad news that you Ypoissant (maybe) can’t spend more time coding the new raytracer. Hopefully you’ll get some help from other coders and the new raytracer will be in next Blender version. I’m really looking forward to this. In my tests, current Blender’s raytracer is one of the major slowdowns in complex scenes with complex raytraced materials (which i do a lot in my projects).