Displacement maps and render time

[marvsweden]

When I add a simple displacement map to any of my materials the render time goes through the roof. I mean to the point of it being totally unusable. Without displacement my scene renders in about 10 minutes with my current settings. When I apply a displacement map I practically see a completely black screen for at least 30 minutes.
I would say that this behaviour is regardless of "quality" settings in the option panel. I've tried changing Image sampler and GI-settings, lowering subdivs for materials and so on but I can't seem to get the rendering to speed up when I'm using any kind of displacement. As soon as I disable the displacement map the render times are back to normal.

Is there a smart way of using displacement maps without having super long render times? Am I missing something here?

[andybot_cg]

yes, you can pre-calculate the Light Cache and Irradiance map with displacement turned off. Then save those maps, and render the final render using the maps "from file" and with displacement re-enabled.

[marvsweden]

Ok, interesting. Thanks for the tip, I'll try that.