OpenCL rendering with Reality/LuxRender - results so far

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TransformerMan
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Joined: Tue May 03, 2016 3:50 pm

OpenCL rendering with Reality/LuxRender - results so far

Postby TransformerMan » Wed Aug 01, 2018 4:41 pm

Well. many attempts later, my personal conclusion is this: Reality default skin materials are simply too complex to render with LuxRender openCL. At least this is true for my setup (24GB RAM, AMD R9 390 8GB GPU).

It's not a hardware limitation, it's a problem in the software stack (possibly limited to AMD, I don't know.) The openCL kernel compiling step uses so much system RAM that a scene with 2 figures needs 20+ GB, which is beyond what my system can handle. Even a scene with one figure is vary taxing. The compiling step takes a long time (can be 20 min or more) and it uses a lot of RAM (12GB is not unusual). It's extremely frustrating, because once the scene actually starts rendering, I get a decent image in about 5 min. (It's not a complex scene.)

I finally got around to systematically trying to reduce scene complexity, and found that, on my system at least, removing SSS and all bump maps brings it down to tolerable levels. openCL kernel compiling step goes down to less than 2 min (1 figure), and even using 2 figures (with clothes) is now possible (5 min kernel compiling, <8 GB RAM)

Lack of skin bump maps is not noticeable, unless for closeups. Lack of SSS changes the skin tone, but that can be largely mitigated in most scenes. So my advice is, if you're trying to render with openCL, remove them. :)

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sigstan
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Location: Denmark

Re: OpenCL rendering with Reality/LuxRender - results so far

Postby sigstan » Sat Aug 18, 2018 12:50 pm

Hi TransformerMan

Don't know if you have looked in the Reality render settings guid, that I did a long time ago:
http://preta3d.com/forums/viewtopic.php?f=23&t=536

Max path length comes to mind as one of the parameters you should try to experiment with. Also please note that resolution is one of the key factors in whether your render will succeed or crash. Try a really low res version first and then up the res until you hit crash point.

Finally I suspect memory consumption is bigger than expected because of the render pipeline that Reality is using. Using the legacy Luxrender scene definition language means a conversion is needed and some of the comments on the old Luxrender forum seemed to imply, that this meant doubling the VRAM requirements.

I don't really spend much time trying to use OpenCL anymore. It was a nice idea, but unless you want to settle for single figure portraits or very simple scenes, it is not really useable. Add in the multitude of issues related to drivers and hardware detection and you have a mess. This is also why I have more or less stopped commenting on OpenCL issues.
/Sigstan

TransformerMan
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Joined: Tue May 03, 2016 3:50 pm

Re: OpenCL rendering with Reality/LuxRender - results so far

Postby TransformerMan » Sat Aug 18, 2018 4:46 pm

Hi Sigstan!

Yes, I've perused your guide several times over the years. Many thanks again for creating it! :)

I've reduced max path length as low as Reality will let me (8 - I've tested editing the LXS and found that I could really live with 4 for many scenes, but I'm usually too lazy and just let it use 8.)

Also using OpenCL only (no boost, last I tried I got a blue screen), GPU only (gotta watch Reality here, it keeps reselecting the CPU openCL device). No FF removal. No noise aware. MonoDir + Sobol. Auto light strategy.

I think this is the best I can do. For the stuff I currently play with, I can live with the restrictions, but yeah.. GPU rendering is a mess in Reality/LuxRender 1.6.

Unfortunately, it doesn't feel like CPU rendering is worth investing in further. I have 3 decent PC's to render on for networked CPU renders, but the time & energy spent is ridiculous compared what could have been done much more cheaply with GPUs.

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sigstan
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Location: Denmark

Re: OpenCL rendering with Reality/LuxRender - results so far

Postby sigstan » Sun Aug 19, 2018 12:07 pm

Sounds like you tried a lot of things, so you're probably right.

CPU-rendering is slow, but then it always was and it doesn't really bother me, as long as I get the results I want. It would be nice though, to be able to use the GPU speed for faster renderings and it will eventually happen. Just not with the current GPU technology/software.

As a side note Reality is overdue for makeover that could shore up the GPU rendering a bit, but I'm starting to doubt it will happen. With the introduction of Iray in DS the entire market situation has changed and adding the flux state that Luxrender is in, it might be hard justifying any further development at the moment.

But luckily I'm not the one that needs to make a decision on that, and I'm sure Paolo has a better overview than I have.
/Sigstan

TransformerMan
Posts: 36
Joined: Tue May 03, 2016 3:50 pm

Re: OpenCL rendering with Reality/LuxRender - results so far

Postby TransformerMan » Sun Aug 19, 2018 1:57 pm

Yeah, it feels like the writing has been on the wall for a few years now. I really don't want to give up on Reality/LuxRender, but it's hard to see it bounce back from the current situation.

I've been looking at Blender lately. I would love something that gave us a seamless bridge between DS and Blender. Then we would have up-to-date LuxCoreRender support, as well as Cycles and the new thing, EEVEE, none of which are exclusively dependent on the proprietary CUDA interface, AFAIK.

I guess we'll see what Paolo decides, eventually.

gpanag
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Joined: Sat Mar 05, 2016 11:13 am

Re: OpenCL rendering with Reality/LuxRender - results so far

Postby gpanag » Wed Aug 29, 2018 10:23 am

Which drivers are you using?
You should try with catalyst v15 that have opencl 1.9.

TransformerMan
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Re: OpenCL rendering with Reality/LuxRender - results so far

Postby TransformerMan » Fri Aug 31, 2018 4:11 pm

I'm currently on 18.7.1. Reality lists openCL as "v2.1 AMD-APP - 2639.5".

Are you suggesting that downgrading to 1.9 could be beneficial?

gpanag
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Re: OpenCL rendering with Reality/LuxRender - results so far

Postby gpanag » Wed Sep 05, 2018 8:38 am

I believe so.
There are some issues with luxrender and opencl 2.0 from what I have read in the forums.
From what I remember, it was because nvidia hasn't update to opencl 2.0 since they focus on cuda. As a result, luxrender could not support opencl 2.0 at the time, but the AMD drivers were coming with opencl 2.0.
I have a similar setup as yours (390x) and I can confirm that gpu rendering is more stable with catalyst 15 (opencl 1.9).
Of course, there are other ways to downgrade to opencl 1.9 than downgrading the whole driver. You can keep certain files from opencl and copy them on top of the newest ones that come with the latest drivers, but I haven't tried that method.

TransformerMan
Posts: 36
Joined: Tue May 03, 2016 3:50 pm

Re: OpenCL rendering with Reality/LuxRender - results so far

Postby TransformerMan » Thu Sep 06, 2018 5:15 pm

Thanks for the info! This is worth investigating. :)

TransformerMan
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Re: OpenCL rendering with Reality/LuxRender - results so far

Postby TransformerMan » Tue Oct 02, 2018 2:13 pm

gpanag wrote:there are other ways to downgrade to opencl 1.9 than downgrading the whole driver. You can keep certain files from opencl and copy them on top of the newest ones that come with the latest drivers, but I haven't tried that method.

I just did (as described in http://preta3d.com/forums/viewtopic.php?f=22&t=550&p=7123#p7123) and IT WORKS!!!

Yeah, it's bit early to celebrate, but I've tested it twice by now, on a scene I worked with a few days ago, and the change is nothing short of amazing. With the old openCL driver, the kernel compiling step takes seconds, not 15 min (which was after all my optimizations, I was at 1+ hours at one point), and the RAM footprint fell from system threatening (20+GB) to essentially trivial (3-4GB).

Wow. I would have paid money for this. Clearly, the combination of LuxRender 1.6 and modern AMD openCL drivers is broken, and have been for 2 years.


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