[Bf-cycles] cycles, some questions about GPU

Sebastian Röthlisberger lalli at gmx.net
Wed Nov 16 15:11:24 CET 2011

Hi Brecht,

Thanks for your answers. 

On 16.11.2011, at 14:53, Brecht Van Lommel wrote:

> Hi,
> I guess this can almost turn into a GPU FAQ :)


> 2011/11/16 Sebastian Röthlisberger <lalli at gmx.net>:
>> Cycles GPU Rendering currently is limited by the amount of available memory on the GPU, as far as i know.
>> 1.-will cycles be able to render scenes bigger than the available Memory on (one) GPU?
>>        1b.-if, in future, cycles uses multiple GPUs will it be still limited by the max amount of memory on one GPU or by the sum of all?
> Rendering scenes bigger than available memory is planned to be added,
> but it may be a year or so before I look at that. Multiple GPU's will
> be limited by the max amount memory of 1 GPU.

"will be limited by the max amount memory of 1 GPU" until the "bigger scene than memory" feature is added?

>> 2.-Is the rendering speed mainly determined by GFLOPS?
>>        2b.-if not, can you tell me what is?
> There is no single GPU feature that correlates directly to rendering
> performance, only way to know is to test.

about 2. GFLOPS.
	afaik GFLOPS is not a single feature but (wiki) Floating Point Operations Per Second.

>> 3.-Does Cycles make use of any "newer" NVIDIA technology? I mean will an older GPU (cycles ready) with same specs as a theoretical new One render at about the same speed?
> It doesn't use any specific new functionality, but it benefits from
> improved architecture of newer fermi cards.
>> 4.-Cycles doesn't care about Nvidia SLI, "just" (will) use all GPUs, right?
> SLI should probably be disabled to make multi GPU work even, not sure.
>> 5.-Will cycles care about different GPUs (for example 1xOlder Cuda, 2xNew Cuda)
>> 6.-Will/might it be possible to mix Cuda and OpenCL GPUs?
> Probably using the same GPU's is more reliable, since you get the same
> memory limits and GPU capabilities. If you've got an older GPU, use
> that for drawing and the others for compute.
>> 7.-Is there a chance that, in future, currently older GPUs like gtx 295 will drop out of Cycles support?
> It's possible that some features will not be supported on them.
>> 8-. just for private use: Do you recommend any GPU?
> NVidia GTX 460, 560 and up, with as much memory as possible.
>> Just wondering:
>> 9.-I know you can't tell, but when you think will multiple GPUs be supported (CUDA)?
> In the next few months.

That sounds great

>> 10.-Do you know/predict anything about significant speed differences (of cycles) between CUDA and OpenCL?
> There might be, we'll have to see how far we can get. In principle the
> languages are similar and the hardware the same, but in practice it's
> impossible to predict how it will turn out.
>> 11.- Between 0-100%, approximate about where is cycles development at the moment.
> There is no 100%, it's like asking when Blender will be done. Just try
> it and see if it supports what you need.

Yeah i know,there's never 100%.  I was just wondering about what you "feel". I used cycles a lot and it is already very usable.

> Brecht.

Thank you so much.

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