Displacement = lower cpu usage?

[tourniquetmaster]

Here is something for someone to solve.
I have a scene renders perfectly fine, at (almost) full CPU usage as long as displacement is switched off. I switch the displacement back on (a single carpet material in this case) and my CPU refuses to run above around 30% for the process...
At first it would seem it is limiting itself to one core, but it would be strictly less than that if that was the case.
The CPU is a Core i7 920XM.
Who has any ideas, theories or wild conjecture as to why this is?

[andybot]

Yes, I've noticed displacement can slow vfsu to a crawl, including reducing the usage of the cpu. I would try first subdividing your geometry in sketchup, smaller triangles can help get a better mesh for vray to use. Aftr that, try teaking edge length settings, etc, in vray. When all else fails, go back to bumpmaps

[tourniquetmaster]

I'll give your tips with subdividing the geometry a try.
I messed around with the displacement subdivs and the edge lengths etc already and took it all the way down to 32subdivs. Seemed to provide the best level of detail vs speed. 16 just looked liked a mess although it rendered fast.
Instead of doing the whole render with displacement I took to the old trick of rendering the LC and IR passes without it on, saved them, ran them from file for the final render with the displacement on. Still took a while but much faster than calculating the LC and IR with the displacement on.

I hope that it is just a kink and they are planning on ironing out how vfsu handles CPU management with displacements once Chaos Group decides vfsu is worth their time again.