I am newbie and i don know if it is posiible. I dont know if this is the correct site where i have to suggets it.

I think cycles is a good render but i do not have a good graphic card and cuda is slow. So i have to use cpu. But i can fix the number of treads (i think this is the number of cpu treads that i have, 4 for a quadcore).

Windows 7 have an option to select wich cpus you can use in an application. It is useful when an application eats a lot of cpu, in this case the pc slow down and if imposiible to work, but if you free a cpu the system work well.

If i have a good graphic card, all cpus are free to compute the render and i think that i need only one cpu or two to move de application, and could be useful that i can add a number of cpu to the work of rendering with cuda. So i could render with all my cuda cores and for example two of my cpu, letting 2 treads for my systema and applications. It could improve the power on render.

It could be a future option to use cycles with gpu, cycles with cpu or cycles with gpu and cpu.

I don'y know if it is now implementd so excuse me if is implemented and tell me how to configure my system to do it.

Hey i had this idea a few months ago and i thought the same, not for blender but for all renderers. But then i found a renderer ( arion) that does the job. At present rendering is done in cycles on gpu with cuda kernel so the compiled code cant be run on cpu i guess.