Cycles slow CPU render when using CPU + GPU with GCC 8.3 build #64894
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Reference: blender/blender#64894
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System Information
Operating system: Linux-4.19.42-1-MANJARO-x86_64-with-arch-Manjaro-Linux 64 Bits
Graphics card: GeForce GTX 1060 6GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 418.74
Blender Version
Broken: version: 2.80 (sub 71), branch: master, commit date: 2019-05-20 16:04, hash:
5c9adc1614Worked: ?
Short description of error
Just a simple scene with the default cube and holes on some faces, default light and a monkey inside the cube. Rendering only with CPU goes ok, the same as rendering only with GPU but rendering CPU+GPU the speed is so slow. If you disable the monkey from rendering the speed is ok again with CPU+GPU but if you enable it, it takes a lot. Also, if you add a subsurf modifier to the monkey, it takes even more.
I'm on a ryzen 5 1600 6C/12T, GTX1060 6Gb and 16G RAM setup.bug-object_inside_object.blend
Exact steps for others to reproduce the error
Open the file attached, enable CPU+GPU rendering, disable Suzanne for rendering, render with cycles and check the time. Enable Suzanne for rendering and check the time now. You can also test it with subsurf and without it on Suzanne.
Thanks and best regards.
Added subscriber: @kong357
Added subscriber: @brecht
Testing here on Linux with a Threadripper 2990WX and Quadro RTX 5000, I can't reproduce the issue. This scene renders instantly for any configuration.
What kind of render times are we talking about? Is there something specific about this scene that triggers it, does it happen in other complex files?
Added subscriber: @zixh
I was having a similar issue with some of my own files and was going to file a bug. Testing my setup with the blend file posted in this report, I also have this issue when using GPU+CPU rendering. Disabling the Suzanne head from rendering produces an almost-instant render. Leaving it enabled and with its subsurf modifier shoots the render time to more than 2 minutes (2:16.49 on my last render), with the major hang being tiles rendering on the CPU.
I'm running a Geforce 1080ti and a Core i7 4970k on Ubuntu 19.04.
Added subscriber: @YAFU
Weird...
I can not reproduce the problem with the .blend file above, it render faster with CPU+GPU in my system.
Tested with more recent Blender 2.8 build by myself and with last from buildbot builds. Kubuntu Linux 18.04. Intel i7-3770 and GTX 960. 430.14 drivers.
The issue is exactly the same as Zix mentioned. You can find attached screenshots for render times:
CPU+GPU no suzanne
CPU+GPU with suzanne and no subsurf
GPU only
CPU only
CPU+GPU,suzanne and 2 levels of subsurf
The issue also appears in more complex scenes and, obviusly, the render times are bigger.
I've found that there's no issue with the "oficial" beta from https://builder.blender.org/download/ so I guess it has to be with the compilation process, maybe some libraries installed by the system package manager (pacman in my case), not updated or maybe too new. I'm trying to compile blender with the "--build-all" option in install_deps to see if it helps.
UPDATE: Nope, it didn't help, will keep trying tomorrow.
@kong357 which GCC or clang compiler version are you using?
@zixh are you also using a your own build, or does it happen with the one from builder.blender.org?
@brecht
GCC = 8.3.0
CLANG = 8.0.0
Ok, I think I found where the problem is and I guess it is the c++ executable version. With gcc and c++ 8.3 the problem is there.
This does not work either.
But this just works as expected.
So downgrading C++ to version 7.x works.
I've also noticed that trying to make "overrides" for switching between versions in /usr/local/bin doesn't take any effect so I assume that the compilation scripts looks directly in /usr/bin for gcc, c++, g++ and so which makes it a bit harder to switch between versions. Maybe with "CC=gcc-7" and "CXX=g++-7" could also work for compiling but I haven't tried that :(
Anyways, the problem is gcc/c++ version and needs to be downgraded to version 7.x so now is solved on my side.
Thanks for your time and keep that great work ;)
I was also using a custom build, and the official beta build does not have this issue. I will test downgrading GCC and seeing if that helps.
Update: downgrading GCC seems to have resolved the issue.
Extremely slow CPU rendering speed with CPU+GPU on Cyclesto Slow CPU render when using CPU + GPU with GCC 8.3 buildSlow CPU render when using CPU + GPU with GCC 8.3 buildto Cycles slow CPU render when using CPU + GPU with GCC 8.3 buildAdded subscriber: @Rigoletto
I can confirm rendering a scene is slower with gpu + cpu enabled. For me it look like the tiles are static splitted in the job queue for cpu and gpu. The gpu finishes his queue and stop working. It should take tiles from the cpu queue then.
System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GTX 660/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 388.43
Blender Version
Broken: version: 2.80 (sub 74), branch: master, commit date: 2019-06-28 22:08, hash:
648e8a1f1dAdded subscriber: @Blendify
Changed status from 'Confirmed' to: 'Needs User Info'
Does this still happen with 2.83 from https://builder.blender.org/download/
This issue never appeared in the buider builds cause I guess it is compiling blender with gcc version 7. It will appear when you'll update to gcc version 8 or even the latest 9.
Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'
Added subscriber: @Sergey
Blender uses GCC 7.1 for the official builds, I don't think can accept a report for compiler version that we don't recommend. I will leave this up to @Sergey or @brecht
Do whatever you have to do but I believe, someday, you will update the gcc version and this bug will occur. Just keep in mind ;)
Added subscriber: @mont29
We are using gcc7 for official builds to comply with LTS distros and OpenVFX platform. Does not mean we do not support more recent compilers (most devs actually use gcc 8 or 9 already I think).
Would not consider that as high priority issue currently, but still it's a valid issue to be investigated.
Added subscriber: @marcmat
I did some tests with Blender 2.83, BMW demo:
OS: Debian 10 x86_64
CPU: Ryzen 5 1600AF
GPU: NVIDIA GTX-1660 driver 440.82 CUDA 10.1
Default compiler flags.
- CPU+GPU: OK (just a little slower)
- CPU-only: single color (flat) image
More tests with Blender 2.83, BMW demo:
OS: Debian Sid x86_64
CPU: Ryzen 5 1600AF
GPU: NVIDIA GTX-1660 driver 440.82 CUDA 10.1
Default compiler flags.
Changed status from 'Needs Developer To Reproduce' to: 'Resolved'
@marcmat, thanks for the tests!
This seems like it was a bug / performance regressions in GCC 8.3 that is now fixed. I don't think it's worth trying to work around this in Blender anymore, to me this is resolved.