View Full Version : Dual Cores and Multi-threading

12-17-2005, 04:52 PM
As some of you know, dual-processor machines can take advantage of more than 1 thread per CPU, 8 threads is frequently the fastest setting. I believe this is because it's more efficient to break up the data into chunks so small that the cpus never sit idle waiting for data to transfer to them.

Several tests on my machine ( dual single-core G5 ) reveals that it could benefit from even more threads, based on the fact that rendering 2 scenes simultaneously, each one set to 8 threads, will render 2 frames in less than twice the time of one frame - 20% less time.

With dual-dual-core machines coming onto the market, we may want to be able to spilt the render into even more threads, or we won't be using all the machine's power. We either need a 16 or even 32 thread option, or a different system all together, like bucket rendering.

Captain Obvious
12-17-2005, 05:02 PM
I'm all for a bucket renderer.

12-17-2005, 09:55 PM
I did a few test renders with my AMD 64x2 4400 and 4 threads was consistently faster than 2 or 8.

12-17-2005, 10:26 PM
I did a few test renders with my AMD 64x2 4400 and 4 threads was consistently faster than 2 or 8.
Interesting - that's one dual-core right? Have you gotten that result with different types of scenes?

12-18-2005, 07:39 AM
I'm with Captain Obvious this time... :)

Exactly one thread for each core (or logical core if they feature SMT) is always optimal in terms of overhead.
I can somewhat understand Lightwave avoided the performance drawbacks of scanline raytracing, but it could finally use buckets insted of rasterize triangles in z-order, since i think it has been sufficiently proven that smart bucket ordering improves coherency a lot over scanlining, so statically dividing the image space and rasterize triangles can be considered obsolete, and does also make the transparent plane trick to avoid multiple rendering of pixels obsolete too...

12-18-2005, 10:43 PM
AbnRanger: interesting... with my 4400+ X2, 8 threads is almost always faster.

12-21-2005, 05:53 AM
that's weird... I even posted the results in a past thread. I'll work on a heavier scene, and see how it performs.