CPU usage whilst using GPU acceleration

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Stinkie
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CPU usage whilst using GPU acceleration

Post by Stinkie » Sat Nov 17, 2012 6:50 am

Quick question: is it normal for the cpu usage to be relatively low while gpu acceleration is turned on?

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Polinalkrimizei
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Re: CPU usage whilst using GPU acceleration

Post by Polinalkrimizei » Sat Nov 17, 2012 7:39 am

Quick answer: That depends.

Sometimes my CPU goes as low as around 70% when using GPU, that depends on its power (the faster the CPU the more data it will shovel to the GPU and the more busy it will get).

How low is your CPU usage? What are your specs? Is it a complex scene?

Stinkie
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Re: CPU usage whilst using GPU acceleration

Post by Stinkie » Sat Nov 17, 2012 8:59 am

Pretty low. It rarely goes over 50%, except for when the image is being refreshed. My cpu is a i7-3930K, my gpu a N680GTX Twin Frozr 4GD5/OC. Scene complexity isn't very high, I think -my SketchUp models are generally fairly simple.

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Pibuz
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Re: CPU usage whilst using GPU acceleration

Post by Pibuz » Sun Nov 18, 2012 2:46 am

Sounds like a so-called bottle neck: I'm not a technician, but sounds like your GPU is very fast compared to your CPU power (which is fair good already, I'd say). Lycium will surely add some more precise info :)

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dag
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Re: CPU usage whilst using GPU acceleration

Post by dag » Sun Nov 18, 2012 3:28 am

Pibuz wrote:sounds like your GPU is very fast compared to your CPU power
Wouldn't then the cpu use more since it has to feed the gpu faster?

My cpu uses 100% and that's an i7 with hd 5770.
Are you using all cpu threads?

Stinkie
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Re: CPU usage whilst using GPU acceleration

Post by Stinkie » Sun Nov 18, 2012 3:42 am

Pibuz wrote:Sounds like a so-called bottle neck (...)
That's what I figured, though I'm no expert either. Dammit, my gpu is too fast! Ah, luxury problems! :)

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Pibuz
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Re: CPU usage whilst using GPU acceleration

Post by Pibuz » Sun Nov 18, 2012 3:48 am

er..busted! :lol: :lol:

I don't know what I'm talking about precisely, I just liked the bottle-neck figure of speech :lol:
I only know I'm currently experiencing a similar issue, running on a machine with a GTX480 and an old q6600 quad core

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CTZn
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Re: CPU usage whilst using GPU acceleration

Post by CTZn » Sun Nov 18, 2012 5:46 am

The case is sounding fishy to me to be honest.

Ideally, when the CPU is not at full throttle that would mean that the GPU can not process the CPU data fast enough.

That's unlikely, given the common reports of modern GPU's being throttled by the CPU, not the other way around.
Stinkie wrote:Quick question: is it normal for the cpu usage to be relatively low while gpu acceleration is turned on?
No, not according to a mass of reported behaviour.

So yes it's a bottleneck, but not as one would expect, hence the topic isn't it.

I'm not an hardware amateur either, but if the "Twin" refers to a double core embedding perhaps is Indigo currently able to mobilize just one.

Did you download the latest drivers ? dag's suggestion is making sense as well, just in case.

To be clarified IMHO.
obsolete asset

Stinkie
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Re: CPU usage whilst using GPU acceleration

Post by Stinkie » Sun Nov 18, 2012 8:22 am

Downloaded the latest drivers -no change. I checked whether I'm using all threads, and I am.

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Zom-B
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Re: CPU usage whilst using GPU acceleration

Post by Zom-B » Sun Nov 18, 2012 11:03 am

CPU & GPU usage is very related to the scene! A exterior often lets your GPU cry, since a lot of rays get bounced back into space and killed early and for interiors and endless bouncing rays the GPU needs to wait for the CPU.
(I hope I don't mixed that up!)
polygonmanufaktur.de

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galinette
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Re: CPU usage whilst using GPU acceleration

Post by galinette » Mon Nov 19, 2012 8:18 pm

Don't forget the bus and I/Os when thinking about bottleneck. CPU and GPU are not the only two components that can limit the speed : the bus between the two has a limited bandwidth and non-zero latency, that can clamp performances.

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Stinkie
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Re: CPU usage whilst using GPU acceleration

Post by Stinkie » Tue Nov 20, 2012 7:55 am

Guess I'm scr*wed. 8)

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CADMonkey
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Re: CPU usage whilst using GPU acceleration

Post by CADMonkey » Wed Nov 21, 2012 9:32 pm

I find this also.

I can quite happy work on other projects whilst rendering using GPU. (I actually find it pretty handy)

my system is i7-2600 (3.4GHz)
16 GB ram
Nvidia Qadro 4000 GFX card

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