cutting down pre-processing

[biliousfrog]

I've got a scene that uses a few material nodes and the pre-processing is having a massive hit on the render times. What I'd like to know is:

What materials use the pre-processing, what is being calculated during the processing and how can I get round it or cut it out altogether?

I originally thought that it was something to do with the reflection blurring and interpolation but I've disabled all that and it's still doing it.

[jameswillmott]

I think all Material nodes can preprocess as part of their interpolated reflections/refractions, Fast Skin does it by default, as do some of the SSS nodes.

You can turn them off with a simple switch inside the Material node usually...

[biliousfrog]

I've tried turning off all reflection blur and interpolation but it's still pre-processing, I think that it's just something that the material nodes do so I'll have to try going back to layers and see how I get on.

[toby]

I've had pre-process continue even after I've switched off sss, had to remove it or reload the scene and switch it off before rendering. Seems like the preprocess part of the render doesn't know it's been switched off.