[Bf-cycles] Tiles sizes - impact on RAM and speed

[Brecht Van Lommel]

On Sun, Feb 10, 2013 at 5:52 PM, Ole Jakob Skjelten <olesk at pvv.org> wrote:
> Thanks a lot for that Brecht! My understanding is that *reducing* tile sizes
> only has a positive effect with regards to reducing the size of the output
> buffer, which is in most cases is a rather small part of the total RAM eaten
> by Cycles, and thus, unless you you're in a desperate
> I-only-need-10MB-more-RAM-to-render-on-my-GPU scenario, increasing the tile
> size for speed benefits is the more likely scenario. Would you agree?

Yes, I agree. Maybe if you have a ton of render passes, but otherwise
you can quite safely set it quite large.

> It's also my understanding that, using CUDA, keeping your tiles to multiples
> of 16 pixels helps speed (or rather prevent wasting GPU cycles)? And
> finally, does it help to operate with tiles that are multiples of the full
> render resolution, or should one use same values for x and y direction
> (square tiles) instead?

Multiples of 16 might indeed help, I'm not quite sure if this true in
general though and if this perhaps depends on the particular GPU.
Multiples of the render resolution will help if you use big tiles,
since otherwise you can get some smaller tiles to fill up the full
render.

Brecht.