Around 55% Reduced render time by disabling "Use Spatial splits".

Here a trick that might work for more people.
This week i got to test a Miner station, it got 7GPU’s and a low performance CPU (dual core).

I noticed in the thread " using a miner station for rendering ".
That calculating the BHV and uploading to GPU’s took about 70% of my frame rendering time.
Apparently CPU’s wait till GPU’s are ready and then start this BHV math, and then the GPU get a workload again.

Then i thought my GPU’s are the most powerfull, if the CPU eats time by performaing BHV calculations.
And as this process is not allready starting for the next frame while the current frame is rendering (bad threading).
Then maybe i be faster without this CPU pre-processing.

Well leaving out the Spatial splits option (as it is often recommend)
(Even the comment of it says longer builder time faster render)
But in my case disabling this render option turned my frame render time from 1.10:59 to just 31:75 seconds.

So perhaps this tip is usefull to others as well.

On a side note, the CPU load is much lower, the system seams more responsive as well.

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The issue with the Use Spatial Splits option now is that the build times become astronomical when you start throwing microdisplacement into the mix (as if the BVH builder itself does not know what to do with such a detailed and high-polygon mesh).

I just keep the option off now since a lot of my scenes have at least one object with microdisplacement. There’s also considering the fact that it can’t use the newer time steps for things like deformation blur, so it might not be a real loss to see the option removed.

Is there maybe some benchmark scene for that?,
When the current animation job finishes (in about a day)

Currently I’m comparing a renderstreet job of last week, against this beast of gpu’s :slight_smile:
So far the time per frame seams shorter about 75% ; however renderstreet has more servers.
What they render in 2 hours, might take me still a day.

we’re in the process of deciding to keep the beast for blender only.
blender and mining or only for mining, or perhaps in the future renting out GPU cloud time.
Or maybe use more mining rigs for it, then we could do a job like that under 1 hours.

I was just hitting this issue here, and I realized that Spatial Splits does more harm than any good with my current scene which just has bunch of highres organic characters. it seems like not much progress in 2.80 regarding BVH.

Does anyone have any example rendering where BVH accel did really helped for real?

The lines below explains the issue a bit by gandalf3

Use Spatial Splits: According to the tooltip, enabling this makes building slower and rendering faster. However, according to the wiki BVH building without spatial splits is optimized (multithreaded) and building with spatial splits is not (yet), so leaving this disabled might be faster overall for now.