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What types of corrections use the GPU to render and which use the CPU?

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Brian Carrigg
What types of corrections use the GPU to render and which use the CPU?
on Sep 23, 2014 at 12:17:36 pm

Being a bit new to Resolve, I hope I can phrase this question in a way that makes sense. I've been using Resolve Lite for about a year, and we've now moved up to the full Resolve 11 paid release.

The computer I am on is a university owned machine, and upgrading is not an option at the moment. Please keep this in mind with your responses. I am well aware of what a faster machine will do for us, but the decision and money are not in my hands.

I am trying to figure out which operations within resolve will cause the GPU to be heavily utilized, and which operations rely more on the CPU. The reason for this is that the Mac Pro I have to work with gets around 35-45 FPS renders on certain projects, but 1-2 FPS on others, and the CPU shows 10-15% load during render. Everything I work with is 1080p, 29.97fps, Prores 422 footage, either from the BMCC, or from the AJA KI Pro. I have several SSDs that I am using (Sandisk Extreme Pro 480GB) as well as a 2 drive RAID for other graphics and elements to be read from. I make sure to render to a disk this is not being read from.


From what I can tell it seems like basic color grading operations, and most things that apply to the entire frame are processed on the CPU, while things with keys, power windows, blurs, noise reduction, and the like, load the GPU heavily. Is this accurate? I haven't been able to find any conclusive information about this.

The single AMD 5770 in this Mac Pro is not up to such tasks, unless its a short video, or I have all weekend. Which I do, sometimes. But other times I am on a short schedule (shooting footage of an event in the morning, and having a 30 second highlight video to show by afternoon.) In these cases, I want to still use Resolve, but I would stick to simple operations that can render quickly on our 16 cores.


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Juan Salvo
Re: What types of corrections use the GPU to render and which use the CPU?
on Sep 23, 2014 at 2:44:07 pm

Everything is processed in the gpu, except for many of the codecs. ProRes and the like get processed on the cpu. Some camera formats are on cpu, some on GPU, and some are a combo, all of the grading functions are GPU bound.

http://JuanSalvo.com
http://theColourSpace.com


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Brian Carrigg
Re: What types of corrections use the GPU to render and which use the CPU?
on Sep 23, 2014 at 2:58:40 pm

What could be causing the huge disparity in render times for some of my projects then? They're all just prores to prores workflows.


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Juan Salvo
Re: What types of corrections use the GPU to render and which use the CPU?
on Sep 23, 2014 at 4:10:10 pm

Drive speed. What grading functions you're using. If noise reduction is enabled. Could be a hundred things.

http://JuanSalvo.com
http://theColourSpace.com


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Brian Carrigg
Re: What types of corrections use the GPU to render and which use the CPU?
on Sep 23, 2014 at 4:16:59 pm

I avoid noise reduction, since that eats up resources in a hurry, but I was wondering about other functions. Like keying, or curves.

I have checked all my drive speeds, and there is no bottleneck there. Its a single video stream, from one SSD to another.

Playback happens in real time, strangely enough. I went through all of the optimizations in the Resolve manual for that though. So that may not give any indication of actual render performance.


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Marc Wielage
Re: What types of corrections use the GPU to render and which use the CPU?
on Sep 28, 2014 at 8:02:42 am

Blurs can also slow things down. Matheiru Marano has an interesting blog post on different ways to improve Resolve performance:

http://ilovehue.net/?p=461

Getting very fast hardware and very fast drives -- particularly RAID 5 arrays with high-speed i/o -- will help quite a bit.


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