CPU and GPU run low when using Iray

kliewer

Hello everybody,

as I can see from your comments, you guys have good knowledge concerning Iray and cpu/gpu usage.
I have some problems with rendering an architectural scene:

Due to the big amount of grass, I divided that scene into four regions which are rendered separately - one after the other. Each time I render a region grass is deactivated outside the region. The reason is saving RAM, because it is limited to 16 GB. The first three regions haven't been a problem, so approximately 75% of the final picture are good and without noise. CPU and GPU ran fine and I saved the picture-parts after ca. 12 hours.

When rendering the last part, cpu starts as usually. After ca. 10 minutes CPU goes down from 90-100% to ca. 15%. The gpu is also down to 15-20%, although 11 of 16 gb RAM are used.
When continue rendering the picture it does not improve (i don't see any changes) and there is a lot of noise after 12 hours. It is not comparable to the other three parts, which were made in the same way. I did not change any setting in Iray or in windows.

I don't understand that result. Do you have any clue, why cpu is going down and gpu is quiet low at the beginning? I attached a th picture for better understanding. The region on the right side looks worse the other...

Intel (R) Core (TM) i7-4770K CPU @3.50 GHZ, GEFORCE GTX 680 4 GB RAM, 16 GB RAM

best regards
Eduard