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appleman91
10-29-2007, 08:42 AM
Hi

Does anyone know why when rendering using a multi processor machine it starts using all the available processors but then as the time goes on it uses less and less.

For example, this morning I was rendering a frame for an illustration, Activity Monitor said it was using 770% CPU usage, on this 8 processor machine, but after about 30 seconds this droped to 500% then it got less and less untill it started a new AA pass.

Seems a waste of all that power to me.

BeeVee
10-29-2007, 08:55 AM
I take it you are using the Classic camera? This is completely normal and LightWave has always worked this way, up until LightWave 9's Perspective camera. Using the Perspective camera will see all your processors running at full speed for all multithreaded portions of rendering.

B

gerry_g
10-29-2007, 09:16 AM
Using the Perspective camera will see all your processors running at full speed for all multithreaded portions of rendering.


Yes and no, in the irradiance pass of a final gather render I often note that although it's using all eight threads it fluctuates between 850% and say 350% of total bandwidth for quite prolonged periods, also many post process effects are not multi threaded, Bloom for instance, which ironically is way way slower in 9.3 than any previous build.

Captain Obvious
10-29-2007, 09:26 AM
The reason the Classic camera is doing that, is because each CPU gets assigned its own region of the render. Suppose you're rendering an ocean scene, with a simple sky and a really advanced water surface. The lower half will, of course, take a lot longer to render. But Lightwave does not know that, and assigns one CPU to the top half and one to the bottom half. The top half finishes quickly, and the CPU does nothing until the bottom half is done. With the new cameras, when one CPU finishes, it will start helping out the others instead.

appleman91
10-30-2007, 04:40 AM
cheers guys, i just rendered a scene that took 34 minutes on my dual 3.0ghz using 9.2 with the classic camera using the camera you suggested it brought that time down to under 6 minutes. i'm quite pleased...!