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Cycles Rendering Drastically Slower Since 2.8 Update
Open, Needs Triage by DeveloperPublic


System Information
Operating system: Windows-10-10.0.16299 64 Bits
Graphics card: GeForce GTX 770/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.15

Blender Version
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: rBf6cb5f54494e
Worked: (optional)

Short description of error
All rendering done with the cycles engine has been much slower in 2.8 than it was in 2.79. A quick test using suzanne and simple AO baking put the 2.8 render at about 1/4th the speed of the 2.79 render. This is consistent with normal render results I've been getting since the update.

Should also mention that during GPU rendering in 2.8, CPU usage shoots up to 100% while GPU usage hovers around 15-20%. In 2.79, CPU usage hovers around 35-40% and GPU usage shoots up to 20% when the bake starts and then drops back down.



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Event Timeline

Philipp Oeser (lichtwerk) lowered the priority of this task from Needs Triage by Developer to Needs Information from User.Aug 29 2019, 10:13 AM

Cannot reproduce here. (linux, 970m, 430.26 drivers)
Here are my baking times:

2.81master buildbot GPU: 13.99sec
2.81master buildbot CPU: 18.96sec

2.79branch buildbot GPU: 13.34sec
2.79branch buildbot CPU: 18.32sec

This is just a shot in the dark / gut feeling: for me at least nvidia doesnt offer these 436.XX drivers, but is there possibly something wrong with these drivers, I think there was another report that I could not reproduce either (reporter also used these drivers)? Could you check if this has different results with 430.XX drivers?

CC @Brecht Van Lommel (brecht)

Philipp Oeser (lichtwerk) renamed this task from Cyclesw Rendering Drastically Slower Since 2.8 Update to Cycles Rendering Drastically Slower Since 2.8 Update.Aug 29 2019, 10:13 AM

Downgraded from 436.15 to 430.86, no changes in render time or hardware usage.

Philipp Oeser (lichtwerk) raised the priority of this task from Needs Information from User to Needs Triage by Developer.Aug 29 2019, 9:57 PM

OKi, thx for getting back

I can repro on windows, but not as drastic as @Brandon Garvie (Bacn)

2.79 buildbot 18 seconds
2.80 buildbot 24 seconds.

2.79 does seem to use the gpu more efficiently

Think I found what the problem was. In user preferences the cycles render devices setting was changes to 'none', I'm guessing this happened by default in 2.8 for some reason. After switching it to 'CUDA', GPU and CPU usage has returned to what was expected. Blender must have been using CPU rendering despite it letting me still select GPU rendering from the dropdown in the render settings.

Could test it some more, but at this point I think it's safe to say it's just a UI mixup.

Baking here with two gpus only uses one gpu and CPU usage is much higher than GPU usage...

In MSI afterburner percentage is a bit different.. But its the same thing.. CPU has a much higher usage.. 13% on GPU versus 58% on CPU.

The same happens while rendering a scene... Not just baking...

The right parameter to measure is just the use of cuda cores? Because if it is... then it seems to use over 90%