[Bf-cycles] Question about NVIDIA GPU resources capping when rendering

Impossible 3D impossible3d.media at gmail.com
Fri Feb 22 04:50:37 CET 2013

Thank you Brecht for a fast answer and a detailed explanation. It is 
very much appreciated. I see the problem.
What I've noticed though is with a smaller tile size render times grow 
really fast (almost double sometimes, although it's on a frame-by-frame 
basis) although the UI does seem a bit more responsive as you say.

Would it be safe to say that to work around this issue, what we would 
need is:

1 - a dedicated card (in this case the GTX560) for cycles.
2 - an OS/2d rendering card (I've got a 8800GT also which could be used)

Booting Ubuntu with the 8800GT as primary (dvi), and not connecting 
anything to the GTX 560. (am I right here?)
But I wonder... is Blender gonna be able to distinguish between the two 
cards? Is there gonna be an option to use the GTX560 (only) to render ?
Or is it going to get mixed up/uncontrolled results, particularly with 
the Nvidia driver ?

Or maybe there is a way to force it to use the proper card in Blender 
(or Ubuntu, or both)...?


On 13-02-20 08:08 AM, Brecht Van Lommel wrote:
> Hi,
> On Tue, Feb 19, 2013 at 9:20 PM, Impossible 3D
> <impossible3d.media at gmail.com> wrote:
>> I was wondering if someone knew if resources capping was available in
>> the nvidia driver and if Blender could maybe get control over it which
>> would allow such a feature (I was putting forward a suggestion that a
>> textbox option besides the "GPU compute" option that would allow for a
>> maximum percent value to be entered and thus would allow some sort of
>> control by the user, for example during the day it would render frames
>> at 60-80% GPU (and hopefully, the computer would stop lagging), and at
>> night or when afk for a long time, it would go back at 100% GPU). It may
>> not even need this level of granularity in case it's a pain to
>> implement, even a low/medium/high/unrestricted selector would be most
>> welcome.
> We could do better here but it's fairly complicated. The way a GPU
> works is that once you send it a job, it can't do anything else until
> that job is finished, it's not possible to do 80% rendering and 20%
> drawing simultaneously. The problem is that if you send it too small a
> job it will not work efficiently, if you send it too large of a job it
> will not be able to redraw the screen until it's done.
> Using smaller tile sizes will give you smaller jobs and so more
> responsive UI. We could have an extra option here to also do nothing
> after each job, I think this would lower the heat but not necessarily
> make the UI much more responsive.
> But the only way to get really smooth interaction is to use separate
> GPU's for rendering and display, as most GPU render engines recommend.
> Brecht.
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