View Full Version : CPU usage. Is this NORMAL?

06-19-2008, 08:57 AM
Hello, I am rendering a fluid simulation that is taking hours per frame on a double dual-core machine.

In the status panel, LW recognizes 4 threads, but I noticed the CPU usage in the Windows Task Manager is only 25% -- sounds like a single thread to me. It starts out rendering at close to 100%, but shortly drops to 50%, and later to 25%. At 25% it stays for the rest of the render.

It is the same if I use screamer net via a batch file.

Seems wierd that LW is only using a fraction of the processing power available.

IS THIS NORMAL? This project is heavy on the HV's. Could there be some rendering tasks that are not multi-threaded?:stumped:

Link to thread on this project.

06-19-2008, 10:05 AM
Are you using the Perspective camera, or the Classic camera?

From memory, HV's in classic camera don't thread, but in perspective camera they do.

It also single threads when it's doing the initial subd/placement of objects.

06-19-2008, 11:59 AM
Yes, classic camera, I'll try with the perspective camera. Thanks for the tip!

06-19-2008, 12:51 PM
I think that is the render threads
dynamics is * ARRGGGGGG* single threaded

06-19-2008, 01:04 PM
If the dynamics are already processed it is still single threaded to render them with HV's?

If so it sounds like changing the camera type won't help-- bummer.

06-19-2008, 01:29 PM
I use hypervoxels all the time and they are multi-threaded, they happily tie up all 4 of my cores. There must be another issue. What version are you using?

06-19-2008, 02:29 PM
Hi creativecontrol,

I'm using 9.3 on the PC. I've rendered quite a few frames from layout. then switcherd to screamernet on single machine via command line/batch file.

I can't think of anything unusual in the scene-- I'm not even using any plugins or shaders.

Just checked again and it jumped to 50%-- too weird. I HATE to see the system idle at 50% also.

06-19-2008, 03:57 PM
Yes, that certainly is a problem. Try setting your renderer to 8 or even 16threads, that can sometimes divide the scene more effectively. Also, did you try the perspective camera? It is usually more effective at keeping the CPU's busy by dividing the scene in better ways.

06-19-2008, 04:02 PM
If the dynamics are already processed it is still single threaded to render them with HV's?

No, mine uses 100% on all 4 CPUs for rendering.

06-19-2008, 04:31 PM
Classic camera renders the whole image without HVs, and then it fills in the HVs (although HVs do appear in reflections while rendering). Perspective camera renders the HVs while it's doing the rest of the image, which is why it threads properly.

06-20-2008, 06:36 AM
The Perspective Camera did the trick. (you guys are great) I set the camera type to perspective and the antialiasing level to 7, kickstarted screamernet and the Violia! Firing on all four cylinders.

QUESTION: Will the "Perspective Cam" images look different than "classic cam" images?

06-20-2008, 11:57 AM
I think that there could be some slight differences - I've just not noticed any myself.

06-20-2008, 02:31 PM
With no other change but the camera type, the render time dropped down from 12 hrs to a little under 4 hrs per frame. In Photoshop, I compared a cassic camera rendered frame with a perspective camera frame, and could not detect any difference.

(multithreading is a beautiful thing) :)