Switching kernels after reaching 16 samples per pixel

[oglu]

What does that mean?
Switching kernels after reaching 16 samples per pixel.

and
// Warning: line 1: V-Ray : Num samples per thread reduced to 168011, rendering might be slower

[hermit.crab]

The first message is printed after a pre-pass phase, in which information is gathered for the adaptive lights.
The warning is meant for our developers and shouldn't be an issue.It means that the estimated 'samples per thread' for the GPU to be 100% loaded was not saved, because of the GPU memory limit (i.e the scene used all the memory). The warning prints the amount of saved 'samples per thread', which means that the jobs for the GPU would be more, but smaller, resulting in similar rendering times.